The risk of rhabdomyolysis is increased by the concomitant use of simvastatin with drugs that have a significant inhibitory effect on cytochrome P-450 3A4 at therapeutic doses (eg, cyclosporins, mibefradil, itraconazole, ketoconazole, erythromycin and nefazodone) or with fibric acid derivatives or niacin. Simvastatin potentiated the effect of anticoagulants eg, warfarin.