Читать книгу Clinical Pharmacology and Therapeutics - Группа авторов - Страница 100

Effective renal plasma flow doubles by the end of pregnancy but this has been shown to be important in only a few cases; for example, the clearance of ampicillin doubles and the dose must also be doubled for systemic (but of course not for renal tract) infections. The hepatic microsomal mixed function oxidase system undergoes induction in pregnancy, probably as the result of high circulating levels of progesterone. This leads to an increased clearance of drugs that undergo metabolism by this pathway, and there is evidence that the steady‐state concentrations of the anticonvulsants sodium valproate, phenytoin and carbamazepine may be decreased to a clinically significant extent during the second and third trimesters. Therefore, higher doses may be required as the pregnancy progresses.