The Obstetric Patient

Abstract

Pregnancy causes a host of physiological changes which inevitably affect drug pharmacokinetics. Therefore, as drug absorption decreases while elimination increases during pregnancy, the plasma concentrations of drugs are generally reduced. Common drugs used in pregnancy include the uterotonics and uterine relaxants. Other drugs used are the antihypertensives and anticonvulsants (magnesium sulfate). As all drugs cross the placenta to some extent, and therefore some fetal exposure will occur, drug safety remains a concern in pregnancy due to the possible adverse effects of drugs, ingested by the mother, on the fetus. Drugs used during pregnancy have been classified according to how the drugs have been developed and their possible impact on the fetus. The ingestion of many drugs is considered ‘safe’ during breastfeeding because the concentrations of these drugs in the breast milk are usually low. When estimating risk during breastfeeding, factors to be taken into consideration include the infant dose, pharmacokinetics of the drug in the infant and effect of the drug in the infant.