Reduced effects with anti-seizures (phenytoin, phenobarbital, primidone), rifampicin and isoniazid. Reduced effects with glucocorticoids. Medications that cause fat malabsorption eg, orlistat, liquid paraffin, cholestyramine, can interfere with cholecalciferol absorption. Cytotoxic drugs, actinomycin and imidazole antifungal drugs interferes with the activity of vitamin D. Increased levels/effects of aluminum hydroxide, cardiac glycosides, magnesium salts, sucralfate, vitamin D analogue.