Metabolism of propranolol in the human maternal-placental-foetal unit

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Abstract
Propranolol (P) and all of its major known metabolites were found in maternal plasma, cord plasma and neonatal plasma in 10 women at term, irrespective of the P doses administered and the time elapsed (up to 15 h) between administration of the last P dose and delivery. The ratios of cord plasma to simultaneous maternal plasma levels for propranolol and its major metabolites (mean±SD) were: propranolol 0.32±0.17, propranolol glucuronide 0.86±0.36, 4-hydroxypropranolol 1.4±1.0, 4-hydroxypropranolol glucuronide 0.71±0.45 and naphthoxylactic acid 3.0±1.6. P binding in cord plasma at delivery was 67.2±3.9% (mean±SD) which was significantly less (‘t’=13.4,df=13,pt’=3.808,df=4,p<0.02) than the naphthoxylactic acid binding in maternal plasma at delivery (97.6±0.4%). When the simultaneous concentrations of P and naphthoxylactic acid in maternal and cord plasma are compared in conjunction with protein binding and ionic effects, it would seem that metabolism of P does occur in the placental/foetal unit.