Table 3.

Physiological changes and potential impact on PK of drugs.

Pharmacokinetic parameter	Effect of pregnancy	Potential impact on pharmacokinetics	Clinical example
Absorption	Decrease in gastrointestinal motility and gastric emptying time Increase in gastric pH Increase in gastrointestinal blood flow Alterations in enzymes and transporters involved in absorption of drugs	Increase or decrease in the rate of absorption Increase or decrease in bioavailability	Aspirin Cmax decreased by 29% during pregnancy (4) Lower Cmax of metoprolol during pregnancy (5)
Distribution	Increase in cardiac output Increase in total body water and fat Decrease in plasma protein binding	Increase in volume of distribution	Increase in volume of distribution of metoprolol during pregnancy (5)
Metabolism	Alterations of CYP and UGT enzyme activity Increase in hepatic blood flow	Increase or decrease in metabolism of substrates	Decrease in clearance of caffeine (CYP1A2 substrate) during pregnancy (6) Increase in Clearance of lamotrigine (UGT1A4 substrate) during pregnancy as compared to postpartum (7)
Excretion	Increase in renal blood flow Increase in glomerular filtration rate Alterations of enzymes and transporters involved in tubular reabsorption and secretion	Increase in renal excretion Increase or decrease in tubular reabsorption and secretion	Unbound renal secretion of digoxin increased during pregnancy due to increased P-gP activity (8) Increased renal secretion and renal clearance of amoxicillin during pregnancy as compared to postpartum (9)