Thiazide diuretics, calcium, or phosphate: Increased risk of hypercalcemia. Plasma calcium concentrations should be monitored.
Some antiepileptics (e.g., Carbamazepine, Phenobarbital, phenytoin, and primidone): Increased vitamin D requirements.
Rifampicin and isoniazid: Rifampicin and isoniazid may reduce the effectiveness of vitamin D.
Corticosteroids: Corticosteroids may counteract the effect of vitamin D.