The effects of prostaglandin E1 (PGE1) and trimetaphan (TMP) on the plasma concentrations and derived pharmacokinetic parameters of bupivacaine were studied in 14 women after its epidural administration. Patients, whose ages ranging from 35 to 60 years for mastectomy, received 50 mg of bupivacaine without epinephrine injected into the cervical epidural space during PGE1- or TMP-induced hypotension (80-90 mmHg of the systolic arterial pressure) under general anesthesia with nitrous oxide, oxygen and isoflurane 0.3-0.5%. No significant differences in pharmacokinetic parameters for the absorption and distribution of bupivacaine were found between the two groups. However, the mean elimination half-life of bupivacaine was significantly longer in patients with TMP [5.0 +/- 1.7 (SD) hr] compared with those with PGE1 (3.1 +/- 1.4 hr). The total clearance of bupivacaine was greater in patients with PGE1 (345 +/- 150 ml.min-1) compared with those with TMP (248 +/- 66 ml.min-1). The results of this pharmacokinetic study indicate that the plasma bupivacaine concentration decreases more rapidly during PGE1-induced hypotension than during TMP-induced hypotension.