Prazosin kinetics and effectiveness in renal failure.

Single and repeated doses of prazosin were given to 17 hypertensive patients, 5 with normal renal function and 12 with impaired renal function. Blood for prazosin assay was drawn after a 1-mg single dose and after patients reached steady-state levels with their long-term maintenance dose. As blood was drawn blood pressure was recorded. Prazosin absorption was not altered in patients with impaired renal function, and there is no cumulation of the drug when given repeatedly to patients with impaired renal function. Elimination kinetics were virtually identical regardless of degree of renal function. Effect on blood pressure was significantly better at the dosage range of 3 to 8 mg/day than at higher doses of 9 to 20 mg/day. There does not appear to be a direct relationship between the peak plasma prazosin level and the nadir of antihypertensive response. This would seem to indicate that the drug leaves the plasma and goes to the vascular smooth muscle receptor site of action. There appears to be no impairment in prazosin elimination in patients with impaired renal function, and its effectiveness (with diuretic or dialysis) is optimum at 3 to 8 mg/day.