Nifedipine interactions in hypertensive patients have been evaluated, taking into account both the possibility that the inhibition of prostaglandin (PG) synthesis induced by non-steroidal antiinflammatory drugs (NSAIDs) can reduce the antihypertensive effect of nifedipine and the interactions of nifedipine with other antihypertensive drugs. While the inhibition of systemic and renal PG synthesis induced by indomethacin reduces the hypertensive effect of many drugs, it does not change the antihypertensive effect of nifedipine. The combination of two antihypertensive drugs with different mechanisms of action is often needed in the treatment of hypertensives, since it is well known that monotherapy is able to normalize BP in no more than 50% of mild to moderate hypertensives, and the rationale to combine two antihypertensive agents is based on the knowledge that their combination exerts an additive antihypertensive effect when compared with single-drug treatment. While it is well established that nifedipine can be usefully combined with beta blockers, ACE inhibitors, and clonidine, it is still controversial whether the combination of nifedipine with a thiazide diuretic exerts an additional antihypertensive effect. We have previously shown that the acute hypotensive effect of nifedipine in patients with chronic renal failure is greater during sodium repletion than during sodium depletion, and that chlorthalidone, compared with placebo, does not increase the hypotensive effect of nifedipine in essential hypertensives.(ABSTRACT TRUNCATED AT 250 WORDS)