Determinants of bumetanide response in the dog: effect of indomethacin

Four male unanesthetized dogs each weighing 22.0-29.0 kg received 0.250 mg/kg iv of bumetanide before (treatment I) and after (treatment II) indomethacin pretreatment. Lactated Ringer's solution was administered intravenously throughout both treatments at a flow rate of 2 ml/min to avoid fluid and electrolyte depletion. Unchanged bumetanide and indomethacin concentrations were analyzed using high-performance liquid chromatography. Sodium was measured by flame photometry and creatinine by colorimetry. Indomethacin pretreatment did not significantly change the pharmacokinetics of bumetanide, affecting neither the total amount of drug nor time course of drug delivered into the urine. In contrast, indomethacin pretreatment resulted in a dramatic reduction in the 4-hr sodium excretion and urine volume. Therefore, a pharmacokinetic interaction may be eliminated as a possible mechanism for the attenuation, by indomethacin, of the natriuretic and diuretic response of bumetanide. Instead, it appears that indomethacin diminishes the response to bumetanide via prostaglandin inhibition.