Abstract
Maternal and fetal plasma clearance of morphine(M) as well as maternal to fetal and fetal to maternal clearance of M were studied in 4 chronically catheterized pregnant ewes and their fetuses. Morphine sulfate was infused into the ewes at a rate of 0.329±0.06 mg/min for 4 hours. Arterial plasma M concentrations were measured by radioimmunoassay at specific intervals in the ewes and fetuses during and after the infusion. Twenty-four hours later, M was infused into the fetuses at a rate of 0.054±0.013 mg/min for 4 hours and respective M concentrations measured. During the maternal infusion, the steady state plasma concentration of M achieved by the ewes was 97.8 ± 17.6 ng/ml and by the fetuses 14.7± 8.4 ng/ml. During the fetal infusion, the steady state plasma concentration of M achieved by the fetuses was 141.2± 63.4 ng/ml and by the ewes 3.5±1.7 ng/ml. Plasma clearance of M in the ewes was 3369±397 ml/min and in the fetuses was 425± 150 ml/min. The maternal to fetal clearance of M was 65.1 ±40.4 ml/min. The fetal to maternal clearance of M was 84.4± 33.2 ml/min. These results indicate that only 20.0± 5.0 % of the total fetal clearance can be accounted for by fetal to maternal clearance. This suggests that maternal clearance of morphine is not the major route of elimination for the fetus. It cannot be assumed, however, that the remaining clearance is exclusively fetal metabolism since renal excretion of unchanged drug and placental metabolism were not determined.
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Cohen, M., Rudolph, A. & Melmon, K. 237 PLACENTAL TRANSFER OF MORPHINE IN THE EWE. Pediatr Res 12 (Suppl 4), 403 (1978). https://doi.org/10.1203/00006450-197804001-00242
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DOI: https://doi.org/10.1203/00006450-197804001-00242