Obstetrics and Gynecology/Pharmacological Considerations in the Pregnant Female
Pharmacokinetic Adaptations to Pregnancy
The pregnant female undergoes many multi-system physiological adaptations throughout pregnancy. Several of these affect the pharmacokinetic properties of the mother (in some cases requiring elevated drug dosages).
Blood volume increases 40-50% in the pregnant female. This serves to increase the volume of distribution in the mother's body.
Many plasma binding proteins are increased (although the 40-50% increase in plasma volume dilutes the concentration of these proteins, their absolute levels are increased).
Blood flow to the kidneys and liver are increased, therefore metabolism and excretion are increased.
The placenta serves to transfer drugs and metabolites into the fetal circulation, in which they are circulated (potentially for a very long time due to the amniotic fluid cycle) and transferred back to the maternal circulation. Several factors favour placental transfer of drugs such as low molecular mass, lipid solubility, apolarity, and high degree of freely concentrated compound.