[The menstrual cycle and drug pharmacokinetics]

Cyclic variations in circulating hormone levels and the associated physiological changes during the menstrual cycle may modify the pharmacokinetics of drugs. So gastric acidity or gastrointestinal motility variations may alter drug absorption; plasma protein concentration changes may also modify drug binding. Finally biotransformations and elimination may be changed during the menstrual cycle. The few studies on menstrual changes in pharmacokinetics are often conflicting and this factor needs to be better documented.