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Phenytoin metabolism during pregnancy
M J Eadie1, G E McKinnon, R G Dickinson
1Department of Medicine, University of Queensland, Royal Brisbane Hospital, Australia.
European Journal of Clinical Pharmacology
|January 1, 1992
Summary
During pregnancy, epileptic women eliminate more phenytoin as the metabolite p-HPPH, compensating for increased dosage needs. This specific metabolic pathway increases, but others do not uniformly during pregnancy.
Area of Science:
- Pharmacology
- Clinical Pharmacy
- Reproductive Medicine
Background:
- Phenytoin is an antiepileptic drug with altered pharmacokinetics during pregnancy.
- Changes in phenytoin metabolism are crucial for managing epilepsy in pregnant women.
Purpose of the Study:
- To quantify phenytoin metabolite excretion in epileptic women during pregnancy and postpartum.
- To investigate the role of specific metabolic pathways in altered phenytoin clearance during pregnancy.
Main Methods:
- Measurement of steady-state 72-hour urinary excretion of phenytoin metabolites.
- Analysis of 10 epileptic women with documented changes in plasma phenytoin concentrations during pregnancy and postpartum.
Main Results:
- Increased urinary excretion of 5-(4-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) was observed, accounting for 61.3% of the dose in late pregnancy and 48.9% postpartum.
- The increased elimination of p-HPPH correlated with the higher phenytoin doses required during pregnancy.
- No significant increase in other minor phenytoin metabolites was detected.
Conclusions:
- Pregnancy enhances the metabolic pathway for p-HPPH, a major phenytoin metabolite.
- This specific metabolic adaptation helps accommodate increased phenytoin dosage requirements during pregnancy.
- Phenytoin metabolism does not appear to be uniformly enhanced across all pathways during pregnancy.