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The effects of drugs on the fetus and newborn infant are based on the general principles set forth in Chapters 14 of this book. However, the physiologic contexts in which these pharmacologic principles operate are different in pregnant women and in rapidly maturing infants. At present, the unique pharmacokinetic factors operative in these patients are beginning to be understood, whereas information regarding pharmacodynamic differences (eg, receptor characteristics and responses) is still grossly incomplete.



Most drugs taken by pregnant women can cross the placenta and expose the developing embryo and fetus to their pharmacologic and teratogenic effects. However, most drugs, despite entering the fetal compartment, do not endanger the fetus when used in recommended doses. Table 59–1 lists teratogenic drugs in humans. Critical factors affecting placental drug transfer and drug effects on the fetus include the following: (1) the physicochemical properties of the drug; (2) the rate at which the drug crosses the placenta and the amount of drug reaching the fetus; (3) the duration of exposure to the drug; (4) distribution characteristics in different fetal tissues; (5) the stage of placental and fetal development at the time of exposure to the drug; and (6) the effects of drugs used in combination.

TABLE 59–1Drugs with significant teratogenic or other adverse effects on the fetus.

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