PHENOXYBENZAMINE PLACENTAL-TRANSFER DURING THE 3RD TRIMESTER

OBJECTIVE: To report phenoxybemamine placental transfer in the treatme nt of maternal hypertension secondary to pheochromocytoma. CASE SUMMAR Y: A 22-year-old woman diagnosed with pheochromocytoma was medically m anaged at 33 weeks gestation with oral phenoxybenzamine and labetalol until delivery 26 days later. To determine phenoxybenzamine placental passage, at the time of cesarean section simultaneous samples were obt ained from the cord blood, maternal blood, and amniotic fluid. Additio nal blood samples were obtained from the newborn at 32 and 80 hours of life. Mean concentrations of phenoxybenzamine from cord and maternal plasma and in amniotic fluid were 103.3, 66, and 79.3 ng/mL, respectiv ely; the newborn's plasma concentration at 32 hours of life was 22.3 n g/mL. At the time of delivery, the 2475-g male infant exhibited perina tal depression; mild transient hypotension was also noted for the firs t few days of life. DISCUSSION: The fetal-maternal plasma accumulation ratio of 1.6:1 indicates that at this gestational age after 26 days o f therapy, the placental transfer of phenoxybenzamine occurs and is ac companied by accumulation in the fetal blood. CONCLUSIONS: Because of the placental transfer of phenoxybenzamine, mild perinatal depression and transient hypotension may occur in newborns of mothers receiving t his medication. These newborns must be closely monitored during the fi rst few days of life for respiratory depression and hypotension.