Background and objective: Cytochrome P450 (CYP) 2C9 catalyzes the biotransformation of indomethacin to its inactive metabolite O-desmethylindomethacin (DMI). The aim of this work was to determine the effect of CYP2C9 polymorphisms on indomethacin metabolism in pregnant women.
Methods: Plasma concentrations of indomethacin and DMI at steady state were analyzed with a validated LC-MS/MS method. DNA was isolated from subject blood and buccal smear samples. Subjects were grouped by genotype for comparisons of pharmacokinetic parameters.
Results: For subjects with the *1/*2 genotype, the mean steady-state apparent oral clearance (CL/Fss) of indomethacin was 13.5 ± 7.7 L/h (n = 4) and the mean metabolic ratio (AUCDMI/AUCindomethacin) was 0.291 ± 0.133. For subjects with the *1/*1 genotype, these values were 12.4 ± 2.7 L/h and 0.221 ± 0.078, respectively (n = 14). Of note, we identified one subject who was a carrier of both the *3 and *4 alleles, resulting in an amino acid change (I359P) which has not been reported previously. This subject had a metabolic ratio of 0.390 and a CL/Fss of indomethacin (24.3 L/h) that was nearly double the wild-type clearance.
Conclusion: Although our results are limited by sample size and are not statistically significant, these data suggest that certain genetic polymorphisms of CYP2C9 may lead to an increased metabolic ratio and an increase in the clearance of indomethacin. More data are needed to assess the impact of CYP2C9 genotype on the effectiveness of indomethacin as a tocolytic agent.