Intensified hypotensive effect w/ ACE inhibitors, β-blockers, nitroglycerin & sildenafil. Elevated serum K level w/ K-sparing diuretics (spironolactone, triamterene), eplerenone & K supplements. Enhanced antihypertensive effect w/ diuretics (furosemide, trichlormethiazide) & grapefruit juice. Lithium toxicity may occur 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 (erythromycin, diltiazem, ritonavir, itraconazole). Decreased blood conc of amlodipine w/ CYP3A4 inducers (rifampicin).