Effect may be reduced w/ anticonvulsants (eg, phenytoin or barbiturates). Thiazide diuretics; alcohol. Decreased effect w/ glucocorticoids. May increase risk of digitalis toxicity w/ drugs containing digitalis & other cardiac glycosides. GI absorption may be reduced w/ ion exchange resin eg, cholestyramine, colestipol HCl, orlistat or laxative (eg, paraffin oil). Actinomycin & imidazole antifungals interfere w/ vit D
3 activity.