Depression of renal clearance of furosemide in man by azotemia.

The renal clearance of furosemide and tetraethylammonium (TEA) were compared in 10 patients with hypertensive nephropathy. BUN and creatinine ranges were 10 to 88 mg/dl and 0.9 to 3.8 mg/dl, respectively. Diuretics were discontinued 48 hr prior to the study, and 2 consecutive clearances (ml/min/1.73 m2BSA) of creatinine were performed. The patient then received a bolus followed by a constant infusion of furosemide-14C and tetraethylammonium-14C (analyzed by specific methodology for plasma and urine), both in subpharmacologic doses. After 40-min equilibration sequential 20-min clearance periods were obtained. Both the clearance of furosemide (range 17 to 133) and TEA (range 99 to 443) correlated negatively with BUN and serum creatinine and positively with creatinine and urea clearances. Thus, by using a constant-infusion technique we demonstrated that the renal clearance of furosemide is depressed by azotemia in man and that there was greater depression with furosemide than with TEA.