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 (Table 3).
Table 3. Drugs and Herbal Treatments for Reducing Vitamin D Levels.| Type of Medication | Examples |
| Antibiotics | - Rifampin (rifampicin)
- Isoniazid
These antibiotics are commonly used to treat tuberculosis. 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 | |
| Anti-HIV drugs | - Refavirenz (Sustiva, Stocrin, and in Atripla)
- AZT (Retrovir, Zidovudine and in Combivir and Trizivir)
These drugs may reduce vitamin D levels in some people. |
| Anti-inflammatory drugs | |
| Herbal remedies | - St. John's wort and its extracts (Hypericin, Hyperforin)
|
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.
