Effect of cimetidine on the absorption and efficacy of orally administered furosemide.

In six normal subjects who received single oral doses of 400 mg cimetidine and 40 mg furosemide, the area under the furosemide plasma concentration-time curve was increased in two subjects by less than 50%, in two by 59% and 75%, and remained unchanged in two: overall the mean increase of approximately one-third achieved statistical significance. This increase was not accompanied by any significant effects on other pharmacokinetic parameters or urine volume, sodium or potassium excretion during the 8 h subsequent to drug administration. Furosemide produced no effects on cimetidine pharmacokinetics. In another group of subjects, administration of 1.0 g cimetidine/day in divided doses before dosing with 40 mg furosemide produced no significant effects on furosemide plasma levels or in its effects on urinary water and electrolyte excretion.