Influence of renal insufficiency on the pharmacokinetics and pharmacodynamics of terazosin.

Renal insufficiency was not shown to affect the pharmacokinetics of terazosin in fifteen patients receiving oral terazosin (1 mg once daily) for two weeks. Five patients had normal renal function (creatinine clearance 80 ml per minute or more), five had moderate renal insufficiency (creatinine clearance 30 to 79 ml per minute), and five had severe renal insufficiency (creatinine clearance 10 to 29 ml per minute). Urine and blood samples were collected, and blood pressure and pulse rate were determined on days one and 15 of the study. Renal insufficiency had no significant effect on the absorption lag time, rate of absorption, rate of elimination in the urine, volume of distribution, or plasma clearance of terazosin. The plasma half-life of terazosin in patients with normal renal function was 10.0 hours, compared with 8.4 hours in patients with moderate renal insufficiency and 9.8 hours in the group with severe renal insufficiency. There was also no apparent relationship between renal insufficiency and the maximum change in blood pressure or pulse rate. Renal excretion was found to play a minor role in the elimination of terazosin, and this explains the lack of a relationship between renal insufficiency and the pharmacodynamics of terazosin. After the administration of terazosin on day 1 of the study, 1.6 +/- 0.3 percent and 5.1 +/- 1.4 percent of the total dose was excreted in the urine of patients with severe renal insufficiency and normal renal function, respectively. Adverse experiences were reported by four patients and caused one patient to withdraw from the study. Symptoms reported included gastralgia, headache, dizziness, malaise, weakness, and palpitations. The results of this study indicate that terazosin may be safely administered to patients with renal insufficiency without altering the usual dosing regimen.