Medications

Enzymes in the liver and kidneys help convert vitamin D into its active form, drugs or substances that interfere with these enzymes have the potential to reduce vitamin D levels. Also, drugs that increase the enzymes that catabolize vitamin D₃ and vitamin D₂ into inactive forms have the potential to decrease vitamin D levels. Some of the herbal supplements as well as medications are listed as follows:

• Antibiotics: Rifampin (rifampicin) and isoniazid, commonly used to treat TB. Vitamin D levels can sometimes fall after as little as two weeks exposure to these drugs.
• Anti-seizure drugs – Phenobarbital, carbamazepine, phenytoin
• Anti-cancer drugs – Taxol and related compounds
• Anti-fungal agents – Clotrimazole and ketoconazole
• Anti-HIV drugs – Refavirenz (Sustiva, Stocrin, and in Atripla) and AZT (Retrovir, zidovudine and in Combivir and Trizivir) may reduce vitamin D levels in some people.
• Herbs – St. John’s wort or its extracts (hypericin, hyperforin)
• Anti-inflammatory drugs: Corticosteroids

Elevated results may occur in patients being treated with Paricalcitol (Zemplar). This medication is the active form of vitamin D used to prevent and treat secondary hyperparathyroidism in patients with chronic kidney disease and on dialysis. Vitamin D levels should not be tested in patients who have received Paricalcitol within 24 hours of obtaining the sample. Also, exposure to the anti- HIV drug darunavir (Prezista) appears to raise vitamin D levels.