The risk of myopathy during treatment with Atorvastatin is increased with concurrent administration of cyclosporin, fibric acid derivatives, erythromycin, azole antifungals, or niacin. No clinically significant interactions were seen when Atorvastatin was administered with antihypertensives and or hypoglycemic agents. Caution should also be exercised when Atorvastatin is administered with inhibitors of P450 3A4 (macrolide antibiotics and azole antifungals). The effect of inducers of cytochrome P450 3A4 (rifampicin or phenytoin) on Atorvastatin is unknown. Patients should be closely monitored if Atorvastatin is added to digoxin, erythromycin, oral contraceptives, colestipol, antacid and warfarin. No interaction was found with cimetidine.