Increased exposure w/ CYP3A4 inhibitors eg, macrolide antibiotics (eg, erythromycin), anti-HIV PIs (eg, ritonavir), azole antimycotics (eg, ketoconazole), fluoxetine, nefazodone, quinupristin/dalfopristin, cisapride, valproic acid, cimetidine, diltiazem. Decreased exposure w/ CYP3A4 inducers eg, rifampicin, phenytoin, carbamazepine, phenobarb. Increased BP-lowering effect w/ other antihypertensives. Risk of deterioration of heart failure w/ β-blockers. Reduced clearance & increased plasma level of digoxin. Lowered plasma levels of quinidine. Monitor plasma conc of tacrolimus when co-administered w/ nifedipine; consider reduction in tacrolimus dose. Elevated plasma conc w/ grapefruit juice.