Half-lives Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Half-lives and links to relevant pages within the course.
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| 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 |
| 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 |
| 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 |