Intensified hypotensive effect w/ β-blockers, nitroglycerin & sildenafil. Elevation of serum K level w/ K-sparing diuretics eg, spirinolactone, triamtelene, eplerenone, K-supplements. Enhanced antihypertensive effect w/ diuretics eg, furosemide, trichloromethiazide. Enhanced blockade of renin-angiotensin system w/ aliskiren fumarate. Lithium toxicity w/ lithium carbonate. Decreased hypotensive effect & aggravated renal function w/ NSAIDs or COX-2 selective inhibitors (indomethacin). Increased blood conc of amlodipine w/ CYP3A4 inhibitors eg, erythromycin, diltiazem, ritonavir, itraconazole. Decreased blood conc of amlodipine w/ CYP3A4 inducers eg, rifampicin. Enhanced antihypertensive effect w/ grapefruit juice. Increased simvastatin AUC. May increase blood conc of tacrolimus.