Terazosin kinetics after oral and intravenous doses

Terazosin kinetics were followed in normal subjects after intravenous doses of 0.5, 1.0, and 2.0 mg and oral doses of 1.0 mg. Plasma and urine samples were collected for the first 48 and 24 hours. The samples were analyzed by a sensitive HPLC assay developed in our laboratory. Mean calculated peak plasma levels from the 0.5, 1.0, and 2.0 mg intravenous doses were 25.0, 44.1, and 83.3 ng/ml. After a 1 mg oral dose the mean peak level was 19.6 ng/ml. Data were fit to a two-compartment open model with mean elimination phase t1/2 values of 7.9, 8.9, and 10.1 hours for the ascending intravenous doses and 11.6 hours for the oral dose. Mean 0 to 24-hour urinary recovery after the intravenous doses was 14%, 13%, and 11%. It is concluded that terazosin kinetics are linear after oral and intravenous doses.