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The page below is a sample from the LabCE course Vitamin D. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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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.