Phenoxybenzamine placental transfer during the third trimester

To report phenoxybenzamine placental transfer in the treatment of maternal hypertension secondary to pheochromocytoma.

A 22-year-old woman diagnosed with pheochromocytoma was medically managed 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 obtained from the cord blood, maternal blood, and amniotic fluid. Additional 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, respectively; the newborn's plasma concentration at 32 hours of life was 22.3 ng/mL. At the time of delivery, the 2475-g male infant exhibited perinatal depression; mild transient hypotension was also noted for the first few days of life.

The fetal-maternal plasma accumulation ratio of 1.6:1 indicates that at this gestational age after 26 days of therapy, the placental transfer of phenoxybenzamine occurs and is accompanied by accumulation in the fetal blood.

Because of the placental transfer of phenoxybenzamine, mild perinatal depression and transient hypotension may occur in newborns of mothers receiving this medication. These newborns must be closely monitored during the first few days of life for respiratory depression and hypotension.