| Federal drug testing custody and control form (CCF) The federal drug testing custody and control form (CCF) must be used to document every urine collection required by the Department of Transportation drug testing program. At the present time, these include the: Federal Motor Carrier Safety Administration (FMCSA) Federal Aviation Administration (FAA) Research and Special Programs Administration (Pipeline) (RSPA) Federal Transit Administration (FTA) Federal Railroad Administration (FRA) United States Coast Guard (USCG) | View Page |
| Non-federally regulated custody and control form The Non-Federally Regulated Custody and Control Form is most often used in clinics and hospital emergency rooms when drug abuse is suspected, or by companies participating in their state's drug-free workplace program. Be aware that some states mandate the use of a special CCF for their drug-free workplace program. There are significant differences between the Federally Regulated CCF and the Non-Regulated CCF. You are strongly encouraged to review the difference between the two. Unless there are extenuating (which we will discuss next), remember that the two forms are not interchangeable. The Federally Regulated CCF can be used only for urine collections required by the Department of Transportation drug testing program. | View Page |
| Exceptions It should also be understood that a Federally Regulated CCF need not be used in every situation involving a company regulated by the Department of Transportation. For example, if an interstate truck driver slips and falls while standing on the loading dock of a trucking terminal, and the trucking company for which the driver works requires a post-accident drug screen, a Non-Federally Regulated CCF would be appropriate for this collection. The driver was not involved in a safety sensitive assignment. On the other hand, if the driver had an accident while driving, then a Federally Regulated CCF must be used since the driver was in a safety sensitive position when the accident occurred. | View Page |
| Custody and Control Form While the Federally Regulated CCF must be used exclusively for DOT drug screen collections, there are extenuating circumstances when another form of CCF may be used. For example, where a post-accident collection must be made and the collector does not have time to obtain a Federally Regulated CCF. In this situation, a Non-Federally Regulated CCF may be used. The collector should note in the "Remarks" section why the Non-Regulated CCF was used.The use of a Non-Regulated CCF for a Federally Regulated collection is not a reason for the laboratory to refuse to test the specimens nor the Medical Review Officer (MRO) to release the results. The use of a Non-Regulated CCF for a Federally Regulated drug screen is a "correctable flaw," which may include the collector detailing the reason for using a Non-Federally Regulated CCF in a "Memorandum for Record." | View Page |
| Intent of this program This program is intended to provide guidance and training to those individuals who will be conducting both Department of Transportation (DOT) and Department of Health and Human Resources (HHS) regulated urine specimen collections. While this program is more than just an overview, obvious restraints prohibit an in-depth discussion of every procedure or problem that might be encountered. This program only serves as a training program. It does not represent final authority. Every effort has been taken to keep this course up-to-date with current regulations. However, if anything in this program conflicts with the Urine Specimen Collection Guidelines, U.S. Dept. of Transportation, Office of Drug and Alcohol Policy and Compliance (Aug. 31, 2009), that reference prevails and must be followed.Training to qualify as a drug screen collector must include the flawless completion of five mock collections. These mock collections must include the following scenarios and must be performed in the presence of a qualified collector: Two uneventful collections. One collection in which the quantity of specimen is not sufficient. One collection in which the temperature of the specimen is out of range. One collection in which the donor refuses to sign either the donor certification on the Medical Review Officer's (pink) copy of the CCF or refuses to initial the security strips. | View Page |
| Five areas having prerequisites for proper collection Regardless whether you are collecting a Federally Regulated or a Non-Federally Regulated urine drug screen, there are five areas which demand specific prerequisites or conditions prior to performing a proper collection. These are: Requirements for the collection site. Supplies needed to conduct a collection. Criteria that must be met by collectors. Complete and accurate documentation. Proper identification of the donor.We will explore each of these in more detail over the next several pages. | View Page |
| Collection site security requirements All collection sites must meet the following security requirements: Must be able to prevent unauthorized access to the site during collection. Ensure that the donor does not have access to items that could be used to adulterate or dilute the specimen (e.g. soap, water, cleaning agents, etc.) Secure faucets, toilet tank tops, and other appropriate areas with tamper-evident tape if necessary. Ensure that the donor is at all times under the supervision of the collector or other collection site personnel. Provide for the secure handling and storage of specimens. (Specimens should be stored at 4-6° C. The refrigerator used should not be readily accessible to the general public and should be used only for the storage of urine drug screens and other clinical specimens. The refrigerator should be marked with a biohazard sign. No food or drink should ever be placed in the refrigerator.) | View Page |
| Acceptable forms of identification One of the most important aspects of a urine drug screen collection is the correct identification of the donor. It is the responsibility of the donor to provide the collector appropriate identification upon arrival at the collection site.Acceptable forms of identification include: A photo identification such as a driver's license, an employee badge, or any other picture ID issued by either a federal, state, or local government agency. Identification made by an employer or a representative of the employer. In this latter case, the employer or employer representative can describe the donor to the suitability of the collector via a phone call. | View Page |
| If there are several donors waiting to have a drug screen and two or more restrooms are available at the collection site; it is acceptable for the collector to process more than one donor at a time. | View Page |
| Collector applies tamper-evidence seals After dispensing the urine specimen into the specimen vials, the collector, not the donor, removes the tamper-evidence seals from the control form and places them on the specimen vials. Seal "A" goes over the primary vial containing 30 mL; seal "B" goes over the secondary vial containing 15 mL. (When doing a Non-Regulated drug screen, since only one vial would be used, "A" would be the appropriate tamper-evidence seal to use.)The seal must be centered over the lid and down the sides of the vial to ensure that the lid cannot be removed without destroying the seal. | View Page |
| Donor refuses to complete paperwork Refusal to Complete Donor Certification on Pink Copy of CCF or Initial Security Strips.If the donor refuses to complete the donor certification on the pink copy of the CCF, or refuses to initial the security strips after they have been affixed to the specimen vials, this is not considered a refusal to test. Do not debate with the donor. It is the responsibility of the collector to note the fact in the "Remarks" section of the CCF. Failure to do so may result in a Fatal Flaw. The MRO may not release the results of the drug screen unless the collector has noted in the "Remarks" section why the donor certification was not completed.Refusal to Provide ID or Social Security NumberIf the donor refuses to provide the collector with an ID or Social Security Number, this is not considered a refusal to test. The collector must make a notation of the fact in the "Remarks" section of the CCF. Failure to do so may result in a Fatal Flaw. After making the notation, the collector continues with the collection. | View Page |
| Shy bladder The term "shy bladder" refers to a situation where the donor is unable to provide the sufficient amount of urine required for a drug screen.If the donor indicates upon arrival at the collection site that he or she cannot provide a specimen, the collector should begin the collection process anyway and have the donor make an attempt to provide a specimen. If after an attempt the donor cannot provide a specimen or can only provide a specimen of insufficient volume, the donor must be instructed not to leave the collection site and to do so will be considered a refusal to test. The donor should be monitored either by the collector or by another member of the collection site staff. The donor should be encouraged to drink up to 40 ounces of fluid reasonably distributed over a period of up to three (3) hours, or until the donor can provide a sufficient amount of urine, which ever comes first. If no specimen is provided on the first attempt, the same collection container may be used for the next attempt. The donor may keep possession of the container during the waiting period. The same CCF is used. | View Page |
| Observed collection scenarios Scenario 1:A donor was asked to wash her hands prior to picking out the drug screen collection kit. The collector noticed that the donor was washing only one hand.Collector's response:The collector tells the donor that not washing both hands is an indication of possible interference with the testing process and that it could be interpreted as a refusal to test. If the donor still refuses to wash both hands, the collector must stop the collection process, note the refusal on the CCF and notify the DER.Scenario 2:The donor was asked to remove his hat before going into the restroom. As he reluctantly did so, it was noticed that he was trying to conceal a container that was hidden inside the hat.Collector's response:The collector first explains the circumstances to a supervisor. If the supervisor concurs that an observed collection should be done, the collector then tells the donor that a directly observed collection will be conducted because his conduct indicated a possible attempt to adulterate, substitute, or dilute the specimen. The collector marks on the CCF that the collection was observed and notes under Remarks why it was observed. | View Page |
| Responsibilities and requirements for collectors You, as a collector, have a great deal of responsibility in the collection of urine for drug testing. It is imperative that you know, understand, and stay current with the rules and regulations. Do the very best you can to make every collection "error free." A collection site must be ready to demonstrate that it satisfies all requirements. Guidelines now mandate that "Federal agencies" inspect each year up to five percent of randomly selected sites used by the agency. | View Page |
| Description of Specialties (4) Specialists in cytogenetics detect chromosome abnormalities and genetic disorders. Cytogenetics counseling may only be performed by an individual licenses in the cytogenetics specialty at the director level.
Specialists in molecular genetics analyze DNA and RNA to find disease-related genotypes, mutations, and phenotypes in order to detect or predict disease and identify carriers.
Specialists in histocompatibility test to determine tissue compatibility, prevent infections, and investigate and post-transplant problems. Techniques include blood typing, HLA typing, HLA antibody screening, disease markers, flow cytometry, crossmatching, HLA antibody identification, lymphocyte immunophenotyping, immunosuppressive drug assays, allogenic, isogeneic and autologous bone marrow processing and storage, mixed lymphocyte culture, stem cell culture, cell
mediated assays, and assays for the presence of cytokines.
Specialists in andrology and embryology examine gametes and embryos, including production, morphology, number, and motility, to address issues of fertility and infertility. | View Page |
| License on probation An individual whose license that has been put on probation for violating the laws of the Board may be subject to any or all of the following requirements, as assigned by the Board: Practice only under direct supervision of a licensed clinical laboratory personBe reviewed on a quarterly basis by his / her supervisor, with reports submitted to the BoardSubmit a personal quarterly report to the Board describing the individual's progressComplete additional continuing education requirementsConsult a psychiatristNot consume alcohol or use any controlled or illegal substancesAttend AA or NA meetings weeklyUndergo and pay for random drug testingPay an administrative fineFailure to comply with all conditions of the probation will mean that the individual's license will be suspended or revoked. | View Page |
| Kickback and Inducement Violations Offering or taking a bribe, kickback, bonus, commission, or inducement is against the rules of the Board and against the law.
Many companies give away small promotional items, such as pens or note pads, to promote their products. This is legal, but be cautious about accepting more valuable items. This could be seen as a bribe.
All of the following are serious violations of Board, state, and federal rules:Participating in any commissions, bonuses, kickbacks, inducements, or split-fee arrangements from physicians, health care providers, suppliers, hospitals, nursing homes, other clinical laboratories, pharmacies, and other facilities.Exploiting or influencing a patient for financial gain, including promoting, selling, or withholding services, drugs, or referrals. | View Page |
| Capability Violations The accuracy and safety of patient testing depends on the capability and honesty of clinical laboratory personnel.
If an individual's ability to perform testing is influenced by illness, injury, drug use (legal and illegal), or alcohol use, he or she may no longer practice. The Board can order a doctor's exam to determine if illness, injury, drugs, or alcohol is a factor. The individual can get his / her license back after recovery and proving that the condition is no longer a problem.
If an individual commits a crime in any state relating to matters of honesty (such as filing false reports or advertising false services), that individual's Florida license may be suspended.
Other licensed personnel who know that an individual is practicing despite being under the influence of drugs or alcohol, is physically or mentally incapable, has been convicted of a lab-related crime, or is not competent to perform his / her duties are required to report the individual to the Board.
The following are violations of Board rules:Continuing to practice after becoming unable to safely perform testing because of illness or use of alcohol or drugs, or another mental or physical condition.
Continuing to practice after being judged mentally or physically incapable.Being convicted of any crime relating to activities of clinical laboratory science or involving dishonesty or lack of morals.
Failing to report to the Board that one has been convicted of a crime (as listed above), been judged mentally or physically incapable, or had a licensed revoked in another state.
Knowingly allow an unqualified person to perform clinical laboratory duties.
| View Page |
| Which of the following are violations of Board rules? | View Page |
| If you know that a colleague has a drug problem that affects his / her work, you must report the colleague to the Board, your supervisor or director, or to another authority. | View Page |
| Chlamydia trachomatis and Neisseria gonorrhoeae In 1988, Gen-Probe marketed the PACE® System, using non-amplified probes for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae. This product was later followed by the PACE® 2 product line.Amplified assays for both Chlamydia and Neisseria followed in subsequent years, offered by several manufacturers. Automation of at least some parts of the process made it more feasible for clinical laboratories to incorporate molecular methods into their test menus.Roche developed a polymerase chain reaction (PCR) methodology focusing on specific nucleic acid sequences for both organisms. The Roche COBAS® AMPLICOR assay, on a semi-automated platform, obtained Food and Drug Administration (FDA) clearance in 1999. The Abbott LCx® semi-automated platform, based on ligase chain reaction, was also introduced around the same time. Shortly thereafter, Gen-Probe offered their APTIMA Combo 2® Assay, an amplification assay that utilized target capture. Later on, the TIGRIS® automated system by PROCLEIX® was added to provide automated specimen processing, enhancing the efficiency of the product line. Becton Dickenson then entered the arena, with the ProbeTec™, another semi-automated system based on strand displacement amplification.Digene also marketed its hybrid capture assay for Chlamydia and Neisseria. Unlike the other commercial assays, this method did not amplify the target DNA sequence, but instead employed a chemiluminescent methodology to amplify the signal of RNA:DNA hybrids. | View Page |
| Human Papilloma Virus (HPV) and Mycobacterium Human papilloma virus (HPV) is estimated to be the most common sexually transmitted infection in the United States. Digene's hybrid capture assay for HPV received approval by the Food and Drug Administration (FDA) in 2003. Only in recent years have other manufacturers, such as Third Wave Technologies, added this virus to their testing capabilities.Mycobacterium species represented another desirable target for molecular testing. Although some improvements in cultivation and staining techniques had been realized through the incorporation of broth media and fluorochrome staining, identification is still hampered by the growth rate of the organism. Gen-Probe first marketed probes that would allow identification of tuberculosis, M. avium-intracellulare, and M. gordonae in culture positive specimens. These probes greatly streamlined the workup of culture positive specimens.Of great interest to both clinicians and infection control practitioners, is the direct detection of Mycobacterium in clinical specimens. Gen-Probe received FDA approval for its AMPLIFIED MTDâ product for this specific application (in smear positive specimens) in 1995. This method employs isothermal transcription mediated amplification; the amplicons are detected using the same hybridization as the culture confirmation tests. | View Page |
| Detection and Identification of Methicillin-resistant Staphylococcus aureus (MRSA) by Polymerase Chain Reaction (PCR) MRSA presents both clinical and infection control challenges. Because of the increasing incidence of MRSA strains, empiric treatment for serious staph infections is usually vancomycin in the hospital setting. Although PNA-FISH can identify Staphyloccocus aureus more rapidly, it cannot yet differentiate MRSA from methicillin-susceptible S. aureus (MSSA) strains. Early differentiation of MRSA from non-MRSA strains could allow for adjustment from broad spectrum antimicrobial therapy, and reduced risk of development of resistance. Hospital acquired infections have garnered increasing attention from many quarters; MRSA is one of several drug resistant organisms that are of concern. Many institutions have implemented active surveillance culture (ASC) protocols to identify carriers of MRSA, both upon admission, and throughout the hospital stay. Identified carriers are placed under precaution protocols, to minimize risk of transmission to other patients during the hospital stay. MRSA status is also an important consideration for those patients who are being discharged to another facility (long term care or rehabilitation centers). Identifying carriers sooner rather than later can reduce the risk of transmission by earlier implementation of precaution protocols and reduce delays in discharge (and length of hospital stay) in situations where carrier status is needed prior to discharge. PCR methodologies offer the prospect of providing screening results 24 to 40 hours sooner than culture methodologies, depending on the culture medium employed. | View Page |
| Introduction of Molecular Methods One of the first companies to bring a Food and Drug Administration (FDA) approved molecular assay to market was Prodesse. Their Hexaplex® assay was a multiplex assay for the detection of influenza A and B, parainfluenza types 1, 2, and 3, and respiratory syncytial virus (RSV). Employing RT-PCR to detect viral DNA, detection occurred as a post-amplification step, employing peroxidase labeled probes. Published studies in 2001 indicated good sensitivity and specificity, but, higher cost per test. The assay was also found to be labor intensive and lengthy.In early 2008, the FDA approved two assays: Prodesses's ProFlu+™ and the xTAG® Respiratory Viral Panel, marketed by Luminex. The ProFlu+™ assay is a real-time, multiplex PCR. In a closed tube system, it simultaneously detects Influenza A and B, and RSV, utilizing RT-PCR. Total turnaround time, including extraction, is approximately 3 hours.The xTAG® assay detects more viruses. In addition to Influenza A and B, and RSV, the assay detects parainfluenza, metapneumovirus, rhinovirus, and adenovirus. The test process includes amplification by PCR, followed by analysis on a Luminex instrument. This assay provided simultaneous subtyping of Influenza H1, H3, and nonspecific types (which the Prodesse assay did not). However, turnaround time was significantly longer. These assays helped draw an increasing interest in molecular assays for respiratory viruses in general and influenza in particular. But in many laboratories, testing protocols were completely upended in the spring of 2009, with the onset of the swine flu epidemic. | View Page |
| 2009 - Swine Flu The 2009 H1N1 influenza virus was first detected in the United States on April 15, 2009.The virus was a unique combination of influenza virus genes never previously identified in either animals or people; they were most closely related to swine-lineage H1N1 viruses (hence the designation of "swine influenza"). However, epidemiological investigations of initial human cases did not identify exposures to pigs and it became apparent that this new virus was circulating among humans and not among U.S. pig herds.By April 21, 2009, the Centers for Disease Control and Prevention (CDC) began working on development of a new vaccine effective against this new strain. On April 24, 2009, the CDC uploaded complete gene sequences of the 2009 H1N1 virus to a publicly accessible international influenza database. At the same time vaccine development was occurring, work was also being done at CDC to help laboratories more quickly identify the 2009 H1N1 virus in patient samples. A real time PCR assay developed by the CDC was cleared for use by the Food and Drug Administration (FDA) under an Emergency Use Authorization (EUA) on April 28, 2009.The development of an effective, rapidly performed molecular assay was critical, because a CDC evaluation of non-molecular rapid influenza assays indicated that while these tests were capable of detecting the novel H1N1 strain when present in high concentrations, the overall sensitivity was low. Positive results with these assays were useful, but negative results did not rule out infection with influenza. | View Page |
| Beta-lactam antibiotics and S. aureus Antibiotics inhibit bacterial growth by interfering with one or more cellular processes. Beta lactams are a large group of cell wall active antibiotics used to treat a wide variety of infections. S. aureus cell wall synthesis is dependent on the proper functioning of a number of enzymes. The beta-lactam antibiotics exert their effect by binding with one specific type of enzyme, transpeptidase, thus interfering with its ability to catalyze the final stage of peptidoglycan synthesis, resulting in defective cell wall formation. The beta-lactams comprise four main groups of antibiotics; all have the beta-lactam ring as their basic chemical structure: Penicillins (penicillin, oxacillin/methicillin, ampicillin and piperacillin) Cephalosporins Carbapenems Monobactams The spectrum of antimicrobial activity is dependent upon the particular structural modification of the beta-lactam ring. The transpeptidases are commonly referred to as penicillin-binding proteins (PBPs). Different bacterial species have distinct PBPs, resulting in very specific drug interactions. | View Page |
| Beta-lactams and Methicillin Resistant Staphylococcus aureus Methicillin Resistant Staphylococcus aureus (MRSA) is resistant to the beta-lactam antibiotics. The term methicillin-resistant is historically used to describe resistance to any of this class of antimicrobials even though methicillin is no longer the drug of choice. The acronym MRSA persists and is used interchangeably with ORSA – oxacillin-resistant Staphylococcus aureus. Oxacillin/methicillin resistance implies resistance to all penicillins, cephalosporins, monobactams, carbepenems and beta-lactam/beta-lactamase inhibitor combinations. S. aureus intrinsically produces beta lactamase enzymes that breakdown beta lactam antibiotics (i.e., penicillin); these are designated PBP 1 - 4. The beta-lactam resistance of MRSA is determined by the production of a novel penicillin binding protein called PBP 2' (PBP 2a), that has a reduced binding affinity for beta-lactam antibiotics. This allows MRSA strains to continue cell wall synthesis due to the uninhibited activity of PBP2' even in the presence of otherwise inhibitory concentrations of beta-lactam antibiotics.PBP2' is encoded by a mecA gene located on the MRSA chromosome and is widely distributed among Staphylococcus aureus as well as coagulase-negative staphylococci. The mecA gene is carried by a novel mobile genetic element, designated staphylococcal cassette chromosome mec – SCCmec that is integrated into the bacterial chromosome. The mecA gene is believed to have originated in some coagulase-negative staphylococcal strains and was then transferred into S. aureus, giving rise to MRSA. It is likely that SCCmec serves as the carrier of the mecA gene moving across staphylococcal spp. as these mecA genes have never been found without the presence of a SCCmec-like structure. Phylogenetic analyses of international collections of MRSA and methicillin-susceptible S. aureus isolates have revealed that methicillin resistance has arisen in five distinct lineages designated SCCmec I – V, which differ in both size and genetic composition. In recent years, the gene has continued to evolve so that many MRSA strains are currently resistant to several different antibiotics. | View Page |
| Which are true statements regarding hospital-associated methicillin-resistant Staphylococcus aureaus (HA-MRSA) and community-associated MRSA (CA-MRSA)? | View Page |
| VISA and VRSA Like methicillin, vancomycin exerts its antimicrobial effect by inhibiting cell wall synthesis, binding irreversibly to cell wall precursors – D-alanyl-D-alanine; and attacking sites responsible for cell wall synthesis. Resistance in VISA strains is thought to be due to: Accelerated peptidoglycan synthesis with increased quantities of D-alanyl-D-alanine residues, which bind & sequester vancomycin molecules Thicker cell walls with reduced peptidoglycan cross-linking (impedes progress of drug molecules) Increased glutamine mucopeptides. All strains with MIC ≥4 µg/ml should be considered candidate VISA strains.Cell wall thickening and transfer of genetic material underlie the development of vancomycin resistance. There is evidence to support the transfer of genetic material among vancomycin-resistant bacterial isolates; the Michigan (2002) VRSA isolate acquired the vanA gene via interspecies transfer from a co-isolated vancomycin-resistant Enterococcus faecalis. | View Page |
| Treatment of CDI/CDAD The first step in treating patients with CDAD is to discontinue the causative agent wherever possible. The choice for initial antibiotic therapy depends on the severity of disease. Oral vancomycin or metronidazole remain the mainstays of therapy for C. difficile infection, with vancomycin reserved for patients with more severe disease and/or those who have not responded to metronidazole. Metronidazole is currently favored in guidelines from the CDC on the basis of cost and concern that oral vancomycin promotes colonization with vancomycin-resistant Enterococcus. Oral fluids (water and electrolytes) may be necessary to counteract fluid loss as a result of excessive diarrhea, which can quickly lead to dehydration. Patients with fulminant disease and toxic megacolon may require colectomy. Recurrence of C. difficile infection (CDI) is becoming an increasing problem. Most recurrences happen 7 - 14 days after completion of therapy, suggesting relapse rather than re-infection. If a patient develops a second episode of CDI following initial successful treatment, it is recommended that if possible, the same drug be used to treat the second episode. Contributing factors to recurrent CDI include: Continuing exposure to organisms either through re-infection (via contaminated environment or poor hand hygiene) or an endogenous source, such as C. difficile spores in GI tract. An inability to mount an adequate anti-Toxin A IgM and/or IgG antibody response (i.e., poor host immune response); a likely reason why CDI affects an increasingly elderly population. Unfortunately a vicious cycle can arise whereby the initial treatment prescribed, vancomycin or metronidazole, significally disrupts normal colonic flora reducing colonization resistance and leaving the patient vulnerable to the next recurrent episode.Other treatments including the use of probiotics or anion-exchange resins to absorb toxins, may work in some cases but none work in every case.The goal of all treatment is to reestablish normal colonic flora so as to control C. difficile (over)growth. | View Page |
| Disinfection & Control of C. difficile Infection C. difficile spores resist dessication for months and are known to persist on hard surfaces for up to 5 months. Spores persist even after exposure to air. Epidemic strain B1/NAP1/027 is known to hyper-sporulate, a virulence-associated characteristic of outbreak strains. Healthcare workers are an important vector for transmission as they may carry the spores on their hands or clothing. Alcohol-based hand sanitizers are very effective against non-sporulating organisms but do not kill C. difficile spores or remove the organism from the hands. The CDC recommends thorough hand washing using soap and water for care givers and family members alike.Patients with C. difficile infection (CDI) should be isolated to a single room with a bathroom or cohorted (roomed) together. Staff treating infected patients should use PPE (gowns & gloves) and wash hands after removing gloves. The use of gowns helps to prevent contamination of clothing. Surfaces should be decontaminated using a solution of 10% sodium hypochlorite (bleach), this is effective in reducing environmental contamination in hospital rooms. The CDC recommends the use of bleach for cleaning patient and staff rooms during outbreaks. Control strategies involving reinforcement of Infection control practices rather than drug restriction are more effective. These practices include: Proper education of staff members involved in care of CDI patients Better isolation compliance Use of gloves Frequent and thorough hand washing Environmental decontamination | View Page |
| Clostridium difficile-associated Diarrhea Clostridium difficile-associated diarrhea (CDAD) is a unique hospital infection that occurs almost entirely in patients who have received previous antimicrobial treatment. Anaerobic gut flora are crucial to colonization resistance, so any disruption of the normal colonic flora (through illness, therapeutic procedures or, most commonly, antibiotic use) is essential to the pathogenesis of C. difficile infection. The association of CDAD with antibiotic use is significant. Early attention (1970s) focused on clindamycin but later on (1980s,1990s & continuing today) the cephalosporins, especially third generation, and broad spectrum penicillins (e.g., amoxycillin/ampicillin) were also implicated. The risk of CDAD is increased if C. difficile is resistant to the particular antimicrobial. In the case of clindamycin, C. difficile resistance is variable. Risk of infection due to a clindamycin-resistant strain increases with use of the drug. For the third generation cephalosporins, C. difficile is universally resistant; thus, any toxigenic strain is capable of causing CDAD during cephalosporin use. Other less commonly implicated antibiotics are the macrolides, e.g., erythromycin, azithromycin, clarithromycin. However, prolonged courses of any antibiotics will increase the risk of disease. Even those antibiotics used to treat colitis (metronidazole, for example) have sometimes been reported to cause CDAD.The fluoroquinolones have been in use since the 1980s. Ciprofloxacin was approved in 1987, but it is only in recent years with the emergence of the epidemic strain 027/NAP1/BI, which is resistant to the fluoroquinolones, that this class of drugs has been implicated in Clostridium difficile disease. The fluoroquinolones were initially considered to be low risk but their use has been increasing, both with hospital inpatients and in the community, and fluoroquinolones are now implicated as a risk factor for C. difficile infection. The newer fluoroquinolones, e.g., gatifloxacin, moxifloxacin, have better activity against anaerobes, but poor in vitro activity against C. difficile, thus increasing the likelihood of CDAD. The CDC now recommends that all fluoroquinolones, as a class, be used sparingly as each poses an increased risk for CDAD. | View Page |
| With regards to identifying resistance in Enterococci, which general statements are true? | View Page |
| Selection of Drugs for Testing The panel of drugs selected for testing must take into consideration a number of factors: The laboratory performing the testing The number of drugs that can practically be tested Infection control requirements Drugs that are available in formularies Susceptibility patterns exhibited locally Consideration of the body site of the infection and whether the drug is an appropriate therapy | View Page |
| Introduction Therapeutic drug monitoring and pharmacogenomics are both pharmacy-related areas within the clinical laboratory. Although each is considered a sub-discipline within laboratory medicine, the two fields overlap significantly. In this course, we will provide an overview of each of these laboratory sub-disciplines and discuss the utility, rationale, and practice of each one. | View Page |
| Basic Pharmacokinetics In order to discuss TDM and PGx we need to also introduce the concept of pharmacokinetics. Pharmacokinetics is the study of drug disposition in the body: how and when drugs enter the circulation, how long they remain in the blood, and how they are eliminated. TDM is the clinical assessment of a drug's pharmacokinetic properties. Physicians and pharmacists need to establish that a drug is present at an effective concentration but not at a toxic concentration. The next few pages will describe some of the factors that determine a drug's disposition in the body. These factors ultimately decide the need for therapeutic drug monitoring. | View Page |
| Drug Metabolism The liver plays a major role in converting lipophilic nonpolar molecules (drug molecules) to more polar, water-soluble forms through a series of enzymatic reactions. Drug molecules can be modified by either phase I or phase ll reactions. Phase I reactions alter chemical structure by oxidation, reduction, or hydrolysis. Phase ll reactions conjugate drugs to create products that are water-soluble. | View Page |
| Protein Binding Most drugs are bound to proteins when they circulate in the body. Albumin is a major drug-binding protein in serum. Albumin is an alkaline protein, so acidic and neutral drugs primarily bind to it. If albumin binding sites become saturated, acidic and neutral drugs can bind to lipoproteins. Alkaline drugs tend to bind to globulins, particularly to the globulin, alpha-1 acid glycoprotein. Only free, unbound drugs are able to bind drug receptors and have therapeutic effects. An equilibrium exists in the systemic circulation between a free and protein-bound drug and between a free and receptor-bound drug. This is illustrated in the image to the right. | View Page |
| Other Factors Affecting Drug Absorption and Distribution In addition to protein availability, other factors may affect drug absorption and distribution in the body as a whole or at specific sites within the body. The following table highlights some of these other factors. Factor Discussion Regional blood flow Reduced area blood flow can be seen in diabetics and enhanced blood flow can be seen in tumors. Lipid solubility of the drug The more lipophilic a drug is, the more likely it will enter the central nervous system. The integrity of the GI tract In a diseased gut, an orally-administered drug may not be absorbed as expected. Age Drug kinetics and dispositions change throughout life. In general, metabolism of drugs is reduced in the elderly. Genetics Mutations or deletions in drug metabolizing enzymes can greatly affect a drug's disposition. | View Page |
| Given what you have learned thus far, which of the following statements below do you think is true? | View Page |
| Steady State Most drugs are not given as a single dose but are part of a regimen. It is the physician's responsibility to prescribe a drug so that the concentration of that drug reaches a safe and effective level. The dosing-goal for the prescribing clinician, if multiple doses of a drug will be given, is for both the peak and the trough drug levels to be consistently within the therapeutic range. If a drug is given at intervals that are the same as its half-life, it will take about 5 half-lives to reach steady state. | View Page |
| Why TDM? Pharmacologists determine a drug's pharmacokinetic characteristics empirically during clinical drug trials. From these studies, they are able to determine the solubility and distribution, the average half-life, the levels of protein binding, and the effective concentrations needed for treatment. | View Page |
| Unexpected Concentrations TDM provides a quantitative measure of the circulating concentration of a drug. The physician determines if the dosage of the drug needs to be adjusted based on this information.If a drug concentration is determined to be outside the therapeutic range, it may be for one of the reasons listed in the table below. Reason Discussion Noncompliance Patients may (intentionally or unintentionally) not take the drug. TDM can thus help monitor compliance. Dosing errors The dose may have been erroneous or inappropriate given the patient's condition. Malabsorption The TDM result will reveal if the drug cannot be absorbed well through the gut and an alternative route of administration will be needed. Drug interactions Many drugs interfere with the absorption or metabolism of other drugs. These interactions will be revealed by TDM. Kidney or liver disease Any pathology that affects elimination will cause an elevation in a drug level that will be unmasked by TDM. Altered protein binding Changes in serum proteins can lead to big changes in the amount of free drug in serum. Variations in the genetics of drug-metabolizing enzymes can also affect drug concentrations in the body. This is the field of pharmacogenomics that will be discussed later in the course. | View Page |
| TDM for all drugs? Can all drugs benefit from TDM? Not really. For TDM to be effective and useful, one or more of the following should apply: The effective concentration and toxic concentrations must be well-defined. The pharmacokinetics of the drug are known to be variable. The drug is given chronically. There is the potential for drug-to-drug interactions. The drug exhibits high protein binding. The toxicity will mimic the indication for the drug; toxicity may not be visible during an exam but will only be revealed with TDM. The patient is pregnant, very young, or elderly. Compliance or history with the drug is poor. | View Page |
| Examples of Drugs That are Monitored by TDM Four major classes of drugs are frequently monitored by TDM: Antibiotics Anticonvulsants Immunosuppressants Cardiac medicationsThere are other drugs that are monitored by TDM that are not included in any of the above classifications, but the majority of TDM testing is performed for drugs that are included in one of these four categories. | View Page |
| TDM for Theophylline Theophylline is used as a bronchodilator for treatment of moderate to severe asthma and chronic obstructive pulmonary disease (COPD). TDM is needed for theophylline because the kinetics of the drug are highly variable. It has a narrow therapeutic window, and overdose can result in elevated heart rate, arrhythmia, and CNS excitability. Clearance of the drug is increased in children, smokers, persons with cystic fibrosis, and persons with hyperthyroidism. Elimination is slowed in congestive heart failure and in the elderly. | View Page |
| A physician needs to prescribe a drug with a narrow therapeutic window. He is concerned about possible toxic effects. To assess the upper concentration of such a drug, which time for drawing the specimen do you think makes the most sense? | View Page |
| Sampling Ideally, a drug level would be monitored frequently and consistently, providing the clinician with a detailed pharmacokinetic profile over time. In reality, serum samples are often measured only during relatively infrequent clinic visits, meaning that many days or weeks may pass before a drug concentration 'snap-shot' is taken. | View Page |
| Albuterol is a fast-acting bronchodilator used acutely during asthma attacks. Which of the reasons below explains why TDM for albuterol is not available or common? | View Page |
| Laboratory Methods Immunoassay is the most common technique used by clinical laboratories for therapeutic drug monitoring. Antibodies that recognize drugs can be developed. Although most drugs are much too small to evoke an immune response, scientists can conjugate drugs to immunogenic proteins to produce antibodies that recognize drug-specific epitopes. There are several methods that utilize the principals of immunoassay for detection and quantification of therapeutic drugs in serum. Some of these methods are: Particle-enhanced turbidimetric inhibition immunoassay (PETINIA) Fluorescence Polarization Immunoassay (FPIA) Chemiluminescent assays | View Page |
| Protein Availability and Drug Dosing Drug-binding proteins in serum can fluctuate in disease states. For example, if albumin levels fall, as can occur in liver failure or nephrotic syndrome, less albumin will be available for drug binding; a subsequent dose may produce a toxic concentration of free drug.The image on the right illustrates the loss of equilibrium between a protein-bound drug and a free drug when drug-binding proteins are diminished.Doses of drugs that are highly protein-bound may need to be adjusted in patients with lower drug-binding protein levels. Examples of some common drugs that are highly protein-bound include thyroxine, warfarin, diazepam, heparin, imipramine and phenytoin. | View Page |
| Therapeutic Drug Monitoring Definition Therapeutic Drug Monitoring (TDM) is a branch of clinical chemistry that specializes in the measurement of medication levels in serum. TDM requires quantitative measurements of drugs and/or their metabolites. | View Page |
| Drug Concentration Over Time When a drug enters the body, it reaches a peak concentration that starts to fall as the drug is eliminated. The figure on the right shows a typical kinetic with a drug given intravenously (IV). | View Page |
| Half-life The amount of time it takes for a drug's concentration in the body to decrease by 50% is called the drug's half-life (t1/2).The longer a drug's half-life, the slower it is removed from the body. Most drugs are eliminated from the body in 1 to 3 days, but some drugs with longer half-lives can still be detected in the body weeks after the initial dose. The figure below illustrates a typical kinetic pattern for an oral drug. | View Page |
| Bioavailability Bioavailability refers to the amount of drug that actually reaches the circulation. It is calculated by comparing (in the same subjects) the area under the serum concentration - time curve (AUC) of an equivalent dose of the intravenous form and oral form. This is illustrated in the diagram on the right.For IV drugs, the bioavailability is 100%For oral medications, the bioavailability will be less than 100%, due in part to any of these reasons:* Oral drugs take longer to enter the circulation.* Oral drugs have slower absorption and distribution than IV drugs.* The amount of drug that is absorbed can depend on the status of the GI tract (stomach pH, presence of food, integrity/health of the intestines, speed of the GI tract, etc.)For oral drugs to be effective, bioavailability typically should be greater than 70%.Not all of a drug taken orally is able to have a pharmacologic effect; the dose would need to be higher than an IV dose.Since the absorption of an oral drug is slower than an IV drug and the drug takes longer to enter the circulation, clearing the drug will also most likely take a longer time. | View Page |
| Steady State Example If the drug Gentamicin has an elimination half-life of 12 hours and is given every 12 hours, the drug should reach steady state after 5 half-lives (60 hours). Notice in the diagram that this kind of dosing results in a 'sawtooth' pattern. Peaks correspond to the times right after the drug is taken; troughs correspond to the times right before the next dose. | View Page |
| Peak and Trough Sampling Times To assess drug concentrations during the trough phase, blood should be drawn immediately before the next dose. To assess peak levels, the time for drawing depends on the route of administration: Oral: One hour after drug is taken (assumes a half-life of > two hours) IV: 15-30 minutes after injection/infusion Intramuscular (IM): 30 minutes - one hour after injection | View Page |
| Drug Elimination Most water-soluble drugs are eliminated from the body through hepatic metabolism. renal filtration, or a combination of the two.An alteration in renal function will have a major effect on the clearance of the drug or its active metabolite(s). Decreased renal function results in elevated serum drug concentrations. | View Page |
| Why TDM? However, every patient is unique. Changes in the gut (if the drug is taken orally), genetic variations in the liver's metabolizing enzymes, and the status of organs (like the kidneys and liver) all affect how a drug will be handled by an individual. TDM helps to ensure that a dosing regimen is appropriate for a given patient. | View Page |
| Why TDM? Every drug has a sub-clinical concentration (a concentration at which effective therapy won't be achieved) and a toxic concentration (a concentration at which the drug will be harmful to the patient.)For some drugs, the range between the minimum effective concentration and the toxic concentration is large. These drugs are thus relatively safe. Other drugs have a very narrow therapeutic window and need closer monitoring. This is the role of TDM.Medications with narrow therapeutic windows, like the anticonvulsant carbamazepine (Tegretol), should be closely monitored since elevated doses can cause serious conditions such as agranulocytosis. | View Page |
| When is TDM Not Useful? TDM is not useful for these drugs or in these specific situations: Intracelluar drugs that need to be converted to active forms (like AZT) Drugs in which the effects last much longer than the serum concentrations of the drugs; examples include antineoplastics (cancer chemotherapies) and warfarin Narcotic pain medications where continued use can lead to tolerance such that the levels needed for pain relief in one person would be toxic to another person | View Page |
| Alternative to TDM Some drugs are more efficiently monitored by determining their effects rather than by measuring the serum drug level. Warfarin dosing, for example, is better monitored by measuring the Prothrombin time (PT) and International Normalized Ratio (INR). | View Page |
| TDM for Anticonvulsants Anticonvulsants typically have narrow therapeutic windows. When levels are too low, the risk for seizure remains present. Drug levels that are too high can depress the central nervous system and may even lead to coma. Examples of anticonvulsants that are monitored by TDM include: Carbamazepine (Tegretol) Valproic acid (Depakene) Phenytoin (Dilantin) Phenobarbital Primidone (Mysoline) | View Page |
| TDM for Immunosuppressants Drugs used to inhibit the immune system are part of standard treatment after transplant surgeries. Regarding the use of TDM, there are some reports of hepatotoxicity and nephrotoxicity with some agents, but the main reason for TDM is to ensure that concentrations are adequate to suppress the immune response and prevent rejection. Examples of immunosuppressants that are monitored by TDM include: Cyclosporine Methotrexate Tacrolimus FK778 | View Page |
| TDM for Cardiac Medications Inotropics (drugs used to increase the pumping ability of the heart) and antiarrhythmics may need TDM. The cardiac glycoside inotropics digoxin and digitoxin have narrow therapeutic windows. Overdose can cause vomiting, diarrhea, confusion, visual disturbances, and cardiac arryhthmias. Examples of cardiac medications that are monitored by TDM include: Digoxin Digitoxin Procainamide N-Acetylprocainamide (NAPA) -the metabolite of procainamide Quinidine | View Page |
| PETINIA Particle-enhanced turbidimetric inhibition immunoassay (PETINIA) is a homogeneous competitive immunoassay.Antibody fragments and drug-latex particles will bind to form aggregates that increase the turbidity of the solution. Free drug from the sample competes for the antibody fragment, thereby decreasing the rate of particle aggregation. The rate of aggregation is inversely proportional to the concentration of drug in the sample. | View Page |
| FPIA Fluoresence polarization immunoassay (FPIA) is also a homogenous competitive immunoassay. In this system, fluorescein-labeled drug competes with unlabeled drug from the patient's serum sample for binding sites on an antibody reagent. The patient's sample, presumably containing the therapeutic drug that is being monitored, and the fluorescein-labeled drug are added to a chamber containing antibody for that drug. The labeled and unlabeled drug will compete for binding sites on the antibody. The greater the amount of drug in the sample, the fewer the number of binding sites that are available for the labeled analyte, leaving a greater number of small, free fluorescein-labeled molecules in the solution.When the chamber is excited with plane polarized light, fluorescein will absorb the light and emit it at a higher wavelength as fluorescent light. A small, free fluorescein-labeled drug rotates randomly and faster than it would if it were bound to antibody, interrupting the light and leading to less emission of light. The larger antibody-drug-fluorescein complexes rotate slower and emit more light in the measured plane. A lower level of drug in the patient's sample results in greater emission of polarized light because there are more antibody-drug-fluorescein complexes present to produce light in the measured plane. A higher level of drug in the patient's sample results in a lower emission of polarized light. This inverse relationship between the concentration of the drug and the polarization units (signal) is illustrated in the image below. | View Page |
| Chemiluminescence Chemiluminescent assays use antibodies that are conjugated to enzymes, such as peroxidase or alkaline phosphatase. These enzymes, mixed with chemiluminescent substrates, produce light in the visible spectrum. A direct relationship exists between the amount of drug that is present in the sample and the light units that are produced and measured by the luminometer in the instrument. Assays that use chemiluminescence are more sensitive than immunoassays that rely on the generation of a colored product. | View Page |
| Individualized Medicine It has been said that we live in a new era of "individualized medicine." One of the primary drivers for this idea is the emerging field of pharmacogenomics (PGx). PGx is the study of how individual variations in the human genome affect responses to medications. The term "pharmacogenetics" is also used for this discipline (people in the field use both terms); however, the term 'pharmacogenomics' is becoming more popular since we now know the entire human genome. The primary reason that individuals metabolize and respond to drugs differently is the inter-individual differences in receptor proteins and enzymes that metabolize the drugs. Mutations in these receptor proteins and enzymes can give rise to very different responses to drugs. In PGx, these mutations are referred to as variants. | View Page |
| Polymorphism and CYP450 To discuss PGx, we must first define two terms - polymorphism and cytochrome P450 (CYP450).A polymorphism is a variation in a gene (allele) that affects at least 1% of the population. CYP450 refers to a family of enzymes found predominantly in the liver. CYP450 enzymes work on a variety of substrates (drugs), altering their chemical structures to facilitate excretion in the urine and feces. There are many known polymorphisms in CYP450 enzymes. | View Page |
| CYP450s Many CYP450 enzymes have been characterized, and the substrates (drugs) that each can recognize have been worked out to a large extent. These subfamilies of CYP450 enzymes have all been associated with polymorphisms that can affect drug disposition: CYP1A2, CYP2C9, CYP2C19 and CYP2D6. | View Page |
| Enzyme Abnormalities and Drugs The following is a list of enzymes for which known mutations have been associated with clinical effects. Enzymes Substrates (Drugs) Acetylaldehyde dehydrogenase Alcohol Acetylcholinesterase Succinylcholine Alcohol dehydrogenase Alcohol Dihydropyrimidine dehydrogenase Fluorouracil CYP2C9 Warfarin, phenytoin, losartan CYP2C19 Diazepam, omeprazole (Prilosec) CYP2D6 Many antidepressants, opioids, antiarrhythmics Glucose-6-phosphate dehydrogenase Aspirin, quinidine N-acetyltransferase Procainamide, isoniazid Thioprine methyltransferase 6-mercaptopurine UDP-glucuronosyl transferase Acetaminophen, tolbutamide, irinotecan | View Page |
| Metabolizers When discussing PGx, we classify a person according to his/her phenotype (metabolic capacity for a given enzyme).A poor metabolizer (PM) is a person who lacks the functional enzyme and therefore exhibits decreased metabolism of drugs. This person would require lower doses of a drug that is metabolized by that enzyme. A PM who receives a standard dose is more likely to experience unwanted side effects or toxicity. A PM can also experience diminished effects with drugs that need to be metabolized to active compounds by the enzyme in question.An ultrarapid metabolizer (UM) will require a higher dose than usual since he/she will eliminate the drug more quickly. A UM may be resistant to standard treatments, and it may take some time to adjust the dosage before therapy is achieved.An intermediate metabolizer (IM) has one wild-type (normal) copy of the gene and one absent or dysfunctional copy. The IM group is very heterogeneous.A person with normal enzyme activity is referred to as an extensive metabolizer (EM). This person should respond to standard dosages of a drug. Most people are EM's. This is the population in which most dosing regimens have been worked out in clinical trials. | View Page |
| CYP450 Induction and Inhibition Variables other than mutations also affect CYP450 enzymes. Many drugs are able to induce CYP450 enzymes, and CYP450s can be inhibited by a variety of substances. For example, CYP2D6 can be inhibited by the common medications cimetidine (Tagamet) and fluoxetine (Prozac). Since many patients are on multiple medications and since dietary and environmental factors can change, CYP450 expression levels cannot be solely predicted based on their genotype. Some CYP450 inducers and inhibitors are listed in the table on the following page. | View Page |
| Genotype versus Phenotype Genotyping can give us a definitive profile of a given CYP450 enzyme's mutations. But since there are dozens of mutations usually associated with each enzyme, a complete characterization of a CYP450 is not always realistic. Without complete sequencing of the entire allele, it may not be possible to entirely rule out a mutation in a patient who shows none of the more common polymorphisms. If we consider the number of possible mutations and the possible presence of inducing/inhibiting substances, phenotyping for drug metabolism may sound more reasonable than genotyping. | View Page |
| TDM and PGx Can we use therapeutic drug monitoring (TDM) to assess PGx?TDM of the drug in question can also tell us a good deal about a drug's metabolism and will also take into account all the other variables at play (co-medications, diet, impaired organ function, etc.) However, unlike genotyping and probe-drug testing, therapeutic drug monitoring must be performed during therapy, not before. So, in fact, TDM is not really used to predict therapy in PGx but serves as a confirmation of PGx findings. TDM and genotyping should be considered complementary and can be used in tandem to, first, predict and then verify appropriate serum drug levels. | View Page |
| The Bottom Line By knowing a patient's disposition to specific drugs, the physician should be able to start the patient on an appropriate regimen rather than perfecting treatment based on trial and error. Drugs whose metabolism may prove to be problematic can be avoided, and second-line therapies that are metabolized by different, unaffected enzymes can be chosen. Clinical chemists, pharmacologists, and physicians need to translate knowledge of CYP450 polymorphisms into clinically-validated treatment algorithms. Dosing recommendations for PM, EM, IM and UM patients are beginning to appear in the literature for various classes of drugs, and the FDA is encouraging the incorporation of pharmacogenomic testing in the development process for new drugs. | View Page |
| A patient is taking cimetidine for a stomach ulcer. This drug inhibits CYP2D6. The patient is now prescribed amphetamine for narcolepsy. Amphetamine is metabolized by CYP2D6. What would you predict? | View Page |
| A person who is classified as an ultrarapid metabolizer (UM) would need __________ of a drug metabolized by that enzyme. | View Page |
| Warfarin Metabolism The first specific pharmacogenomics (PGx) testing application most labs are likely to encounter is that used in patients taking warfarin. Recent studies have revealed that the variations seen in patients taking the anticoagulant warfarin are due to PGx factors. The consequences of incorrect warfarin dosing are obviously serious, with inadequate doses predisposing patients to thrombosis and higher doses placing them at risk for hemorrhage. The United States' Food and Drug Administration (FDA) recently approved updated labeling for Coumadin (warfarin sold by Bristol-Myers Squibb). The new labeling suggests that physicians incorporate PGx information into warfarin-dosing regimens for patients. Manufacturers of generic warfarin products are now adding similar labeling. | View Page |
| Warfarin Metabolism, continued The genes involved in warfarin metabolism are CYP2C9 and vitamin K epoxide reductase complex subunit 1 (VKOR). Warfarin owes its anticoagulant action to its inhibition of VKOR. This enzyme recycles vitamin K, a critical element for the clotting factors II, VII, IX, and X, as well as for proteins C, S, and Z. There are six CYP2C9 alleles that are known to cause prolonged metabolism of warfarin: CYP2C9 *2, *3, *4, *5, *6, and *11. (Polymorphisms in CYP450 genes are denoted with asterisks.)One-third of the patients that receive warfarin metabolize it differently than expected and experience a higher risk of bleeding.Genetic testing for the two most common polymorphisms (CYP2C9*2 and *3) as well as for VKOR may be able to reduce the variability associated with warfarin dosing response. Labs performing PGx testing can provide general warfarin dosing recommendations based on the patient's genotype analysis. The lab report will indicate whether a patient has a normal, mild, moderate, high, or very high sensitivity to warfarin. For example, a patient who has one CYP2C9 normal wild-type allele (CYP2C9 *1), one polymorphism (CYP2C9*3), and also a VKOR polymorphism is predicted to have a moderate sensitivity to warfarin. This patient should have frequent INR monitoring and possible warfarin dose reduction. It is important to recognize that knowing a genotype does not necessarily guarantee accurate dose prediction; other drugs and/or environmental or disease factors can also alter CYP2C9 activity. Therefore, monitoring the INR is still very important. | View Page |
| CYP2D6 CYP2D6 has received the most attention: It is estimated that about 25% of common drugs are metabolized by CYP2D6. CYP2D6 accounts for only about 1% of all CYP450 enzymes, but it is important in the metabolism of about 100 drugs. There are more than 80 genetic variants that have been described in the CYP2D6 gene. The normal, wild-type allele displays normal metabolic activity whereas some of the variant forms have enhanced or diminished activity. The variants can be grouped generally according to the resulting alterations in protein function. The groupings correlate with four major enzyme metabolic capacities (phenotypes): poor, intermediate, extensive (normal), or ultra-rapid metabolizers. | View Page |
| Genotype versus Phenotype Phenotyping involves measuring the metabolism of a probe drug. For example, with CYP2D6, dextromethorphan or debrisoquine can be given to a patient to see how well the drug is metabolized. Both these drugs are safe and extensively metabolized by CYP2D6. By measuring the parent drug and the metabolite in urine, the metabolic capacity of a CYP450 enzyme can be estimated. Such testing is complex and tedious, however, and has not become routine in clinical laboratories. Therefore, genotyping is likely to be the main tool that is used for assessing the PGx of a patient. | View Page |
| References Clinical Chemistry: Theory, Analysis, Correlation, 4th Edition. Lawrence A. Kaplan, Amadeo Pesce, Steven Kazmierczak. New York: Mosby, 2002.FDA Clears Genetic Lab Test for Warfarin Sensitivity. FDA News. U.S. Food and Drug Administration. Available at http://www.fda.gov/bbs/topics/NEWS/2007/NEW01701.html. Accessed June 3, 2008.Goodman & Gilman's The Pharmacological Basis of Therapeutics, 11th Edition. Laurence Brunton, John Lazo, Keith Parker. McGraw-Hill, 2005.Tanaka E, Terada M, Misawa S. Cytochrome P450 2E1: it's clinical and toxicological role. J Clin Pharm Ther. 2000 Jun;25(3):165-75.The Chemistry of Mind-Altering Drugs: History, Pharmacology, and Cultural Context. Daniel Perrine, American Chemical Society Publication, 1996.Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 4th Edition. Carl A. Burtis and Edward R. Ashwood, eds. Philadelphia: WB Saunders, 2005. | View Page |