Protein-bound and free plasma phenytoin during pregnancy

In a clinical study using low doses of phenytoin as an ovulation inducer, the plasma levels and the binding percentages of this drug and the plasma level of its main metabolite, p-hydroxyphenytoin, were monitored. The results show that during pregnancy, plasma levels of both remain stabile and low as compared with those observed in epilepsy treatment. This could be one explanation for the absence of teratogenic effects observed in this and other studies using phenytoin for the same therapeutic aim.