Pharmacokinetics in pregnancy

This chapter discusses pharmacokinetics in pregnancy. Prescription and over-the-counter (OTC) drug use during pregnancy is necessary for many women. Pharmacokinetic information describes how a drug is absorbed, distributed, metabolized and eliminated by the body and how these processes impact plasma drug concentrations. During pregnancy, there is an increase in total body weight. Drug metabolism is another PK parameter that is altered in pregnancy and these alterations are highly linked, as was the case with absorption, to elevated sex hormones. Drug elimination also changes during pregnancy due to a significant increase in renal excretion. A discussion of PK in pregnancy would be incomplete without some mention of the fetal compartment. It has been established that drugs may be subject to metabolism by placental and fetal tissues. In the placenta, the presence and activity of a variety of CYP450 and UGT enzymes has been documented. Studies in non-pregnant participants have clearly demonstrated that disease can have clinically significant effects on PK. The changes to PK parameters during pregnancy that are presented in this chapter should illustrate that PK information is necessary if physicians are to make evidence-based dosage recommendations. In 1993, the FDA acknowledged the need to begin obtaining more detailed information for drugs that could be taken by pregnant women. Women enter into pregnancy with pre-existing disorders and/or develop disorders that demand pharmacotherapy; however, the efficacy of these drugs is altered in many cases because of changes in physiology that ultimately affect PK.