To investigate the influence of gestational diabetes mellitus (GDM) on the kinetic disposition and transplacental and amniotic fluid distribution of metoprolol and its metabolites O-desmethylmetoproloic acid and α-hydroxymetoprolol stereoisomers in hypertensive parturients receiving a single dose of the racemic drug.METHODS
The study was conducted on hypertensive parturients with well-controlled GDM (n = 11) and non-diabetic hypertensive parturients (n = 24), all receiving a single 100 mg oral dose of racemic metoprolol tartrate before delivery. Serial maternal blood samples (0–24 h) and umbilical blood and amniotic fluid samples were collected for the quantitation of metoprolol and its metabolite stereoisomers using LC-MS/MS or fluorescence detection.RESULTS
The kinetic disposition of metoprolol and its metabolites was stereoselective in the diabetic and control groups. Well-controlled GDM prolonged tmax for both enantiomers of metoprolol (1.5 vs. 2.5 h R-(+)-MET; 1.5 vs. 2.75 h S-(−)-MET) and O-desmethylmetoproloic acid (2.0 vs. 3.5 h R-(+)-AOMD; 2.0 vs. 3.0 h S-(−)-OAMD), and for the four stereoisomers of α-hydroxymetoprolol (2.0 vs. 3.0 h for 1′S,2R-, 1′R,2R- and 1′R,2S-OHM; 2.0 vs. 3.5 h for 1′S,2S-OHM) and reduced the transplacental distribution of 1′S,2S-, 1′R,2R-, and 1′R,2S-OHM by approximately 20%.CONCLUSIONS
The kinetic disposition of metoprolol was enantioselective, with plasma accumulation of the S-(−)-MET eutomer. Well-controlled GDM prolonged the tmax of metoprolol and O-desmethylmetoproloic acid enantiomers and the α-hydroxymetoprolol stereoisomers and reduced by about 20% the transplacental distribution of 1′S,2S-, 1′R,2R-, and 1′R,2S-OHM. Thus, well-controlled GDM did not change the activity of CYP2D6 and CYP3A involved in metoprolol metabolism.