Clinical pharmacology of prazosin in hypertensive patients with chronic renal failure.

The clinical pharmacology of prazosin was studied in 10 hypertensive patients with chronic renal failure (group I) and in 9 hypertensive patients with normal renal function (group II). Prazosin, 2 mg, was given orally and blood samples were drawn at intervals for spectrofluorimetric assay. Blood pressure and heart rate were obtained at the same time. In the renal failure group, prazosin induced a significant decrease in systolic and diastolic blood pressures (-19 and -23%, respectively) at 90 min after intake, and these alterations were more rapid and marked than in the normal renal function group. Peak plasma concentration (Cmax) was higher (33.5 +/- 3.7 vs. 20.04 +/- 1.7 micrograms/liter, p < 0.01) and occurred earlier (1.3 +/- 0.2 vs. 2.7 +/- 0.3 hr, p < 0.005) in group I than in group II. The area under the plasma concentration-time curve (AUC0 infinity) was increased in the renal failure group (206.1 +/- 31.1 vs. 112.4 +/- 9.4 micrograms/hr/liter, p < 0.01). Apparent plasma elimination half-life (t 1/2) was not significantly different in the two groups (3.6 +/- 0.4 vs. 2.9 +/- 0.3 hr. ns). The mean blood pressure change (delta MBP%) was significantly correlated with the plasma level of prazosin in the renal failure group (n = 97, r = 0.489, p < 0.001) but not in patients with normal renal function (n = 74, r = 0.297, ns). The hypotensive action of prazosin is greater in patients with chronic renal failure, and the bioavailability or distribution of the drug is altered. Therefore, prazosin dosages should be modified in patients with impaired renal function.