Drug kinetics in childbirth.
AbstractDrugs from a wide range of pharmacological classes are commonly given to women in childbirth, either for a maternal effect or a fetal/neonatal effect. A number of striking physiological and biochemical changes occur during labour and delivery that might alter drug kinetics. The rate of drug absorption from the gastrointestinal tract may be normal in labour provided that narcotic analgesics are not administered concurrently. Altered blood flow characteristics in the extremities could modify drug absorption from intramuscular injection sites. Drug distribution might be altered as a result of the presence of placental-fetal tissues, or as a consequence of changes in, for example, maternal blood volume, concentrations of proteins and other endogenous compounds, cardiac output or tissue perfusion. Although data are scanty on the status of the physiological determinants of drug clearance, that limited information available suggests that drug clearance could be altered in childbirth. The possibility of a placental and/or fetal contribution should not be overlooked when considering the clearance of drugs administered during labour and delivery. Uterine contractions, maternal posture and obstetric medication have been found to affect the extent of some of the physiological changes that occur. Consequently, drug disposition could be modified by these factors.