Prazosin plasma concentration and blood pressure reduction

Abstract

Prazosin was administered to 16 patients with essential hypertension in an initial dose of 0.5 mg, after which the blood pressure (BP), pulse, and plasma concentrations of prazosin were measured at 0,0.5, 1,1.5, 2,2.5,3,4, 6, 8, and 24 hours. The dose of prazosin was then increased over 16 to 20 weeks, and similar sequences of measurements were obtained twice. Eleren patients completed the 20-week course. All patients did not respond in a similar way; two distinct patterns of BP and poise response emerged, although there was no significant difference in the pharmacoklnetic parameters, namely, absorption rate constant (Ka), maximum plasma concentration (Cpmax), time to reach the maximum concentration (Tmax), prazosin plasma halflife (T'/i), elimination rate constant (kel), prazosin plasma concentration-time curre (AUC), and clearance. Patients in Group 1 had a marked reduction (52/30 ram Hg) of BP after the first dose of prazosin, no pulse increase, and needed a small dose of prazosin to maintain an adequate BP response. Patients in Group 3 had a minimal reduction in BP (14/13 mm Hg) after a first dose, a significant pulse increase, and needed a high dose of prazosin to control their BP. We conclude that this effect might be due to a different drug-receptor interaction, and the BP response and dose could be predicted from the response of the first dose of prazosin. © 1982 American Heart Association, Inc.