Reduced levels of active metabolite w/ rifampicin & fluconazole. Increase in serum K w/ K-sparing diuretics (eg, spironolactone, triamterene, amiloride), K supplements, K-containing salt substitutes or other drugs that may increase serum K (eg, trimethoprim-containing products). May reduce lithium excretion. May reduce effect w/ NSAIDs including selective COX-2 inhibitors. Increased risks of hypotension, syncope, hyperkalemia & changes in renal function w/ angiotensin receptor blockers, ACE inhibitors & aliskiren.