Transfer of methadone across the dually perfused preterm human placental lobule

Objective: The objective of the study was to determine the effect of gestational age and P-glycoprotein expression on transplacental transfer of methadone. Study Design: Dual perfusion of placental lobule was utilized. Methadone (200 ng/mL) and its [³H]-isotope were cotransfused from the maternal-to-fetal circuit with the marker compound antipyrine (20 μg/mL) and its [¹⁴C]-isotope. Concentration of the drugs in trophoblast tissue and both circuits was determined by liquid scintillation spectrometry. Results: Fetal transfer rate of methadone in preterm placentas was 19 ± 5.8%, and in term placentas it was 31 ± 9.7% (P < .01). Clearance index of methadone in preterm placentas (0.57 ± 0.2) was lower than in term placentas (0.95 ± 0.3, P < .01). P-glycoprotein expression was higher in preterm than term placentas. Conclusion: The ex vivo transfer of methadone across preterm placentas is 30% lower than in term placentas.