May intensify hypotensive effect w/ ACE inhibitors; 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. Increased renal tubule reabsorption w/ lithium carbonate. NSAIDs may decrease hypotensive effect. Amlodipine metabolism may be competitively inhibited w/ CYP3A4 inhibitors eg, erythromycin, diltiazem, ritonavir, itraconazole. Enhanced amlodipine metabolism w/ CYP3A4 inducers eg, rifampicin. May increase blood conc of amlodipine w/ grapefruit juice. Increased simvastatin AUC.