Drugs in pregnancy. Pharmacokinetics in pregnancy.

Pharmacokinetics describes the handling of a drug by the body - how the drug is absorbed, distributed and eliminated and how these processes determine plasma concentrations of the drug. Changes in maternal physiology during pregnancy influence pharmacokinetics, and this may have important sequelae for drug dosing, especially for drugs for which adverse effects occur at concentrations within, or just above, the therapeutic range. For many drugs absorption is decreased and elimination increased, thus tending to reduce plasma concentrations. There are, however, relatively few specific data on pharmacokinetics in pregnancy, compared to the non-gravid state, because of the obvious ethical issues surrounding studies during pregnancy. Most therapeutic guidelines are thus based on observational studies and basic principles.