Transplacental distribution of salbutamol enantiomers at Caesarian section

Aims To investigate the transplacental distribution of salbutamol enantiomers after administration of racemate to women prior to Caesarian section. Methods Five women about to undergo elective Caesarian section were administered a single 0.25 mg bolus intravenous dose of (R,S)-salbutamol. The time from drug administration to delivery was different for each woman (27-105 min). Maternal and foetal umbilical cord venous blood samples were collected immediately after delivery and the plasma fraction analysed for salbutamol enantiomer concentrations by enantioselective high pressure liquid chromatography. Results The concentrations (mean +/- s.d.) of the active (R) enantiomer of salbutamol in cord and maternal plasma were 0.46 +/- 0.35 and 0.89 +/- 0.50 ng ml(-1), respectively, and the difference was statistically significant (95% confidence interval (CI) of the difference: 0.12-0.74 ng ml(-1)). The corresponding concentrations of the (S) enatiomer of 0.92 +/- 0.45 and 1.11 +/- 0.67 ng ml(-1), respectively, were not significantly different (95% CI of the difference -0.08-0.48 ng ml(-1)). The ratio of (R) : (S) in cord plasma was significantly less than that in maternal plasma (P=0.016). Conclusions Transplacental distribution of salbutamol enantiomers at Caesarian section after prior administration of racemate to mothers leads to concentrations in cord plasma that are significantly less for the active (R) enantiomer and not significantly different for the (S) enantiomer than in maternal plasma presumably due to enantioselective placental-foetal metabolism.