Cimetidine Pregnancy and Breastfeeding Warnings
Cimetidine Pregnancy Warnings
Cimetidine has been assigned to pregnancy category B by the FDA. Animal studies have failed to reveal evidence of fetal harm. There are no controlled data in human pregnancy. Cimetidine crosses the placenta, bidirectionally, by slow, passive diffusion. However, cimetidine has been used safely during pregnancy to treat severe peptic ulcer disease as well as near term for the prevention of Mendelson's syndrome. Cimetidine is only recommended for use during pregnancy when benefit outweighs risk.
Placental transfer of cimetidine is slow. In one study, the fetal/maternal ratio averaged 0.46 two hours after intravenous administration of cimetidine to the maternal placental circuit. Administration to both the fetal and maternal circuits resulted in equilibrium, with the fetal/maternal ratio averaging 1.01, for the duration of the two hour experiment. These data suggest that chronic dosing would result in increased exposure to the fetus compared to exposure following a single dose during labor. There are no adequate data on the safety of cimetidine during the first trimester. Cimetidine has been used safely and successfully during labor to prevent Mendelson's syndrome. The use of cimetidine in this setting does not affect the duration of labor or the pattern or intensity of contractions. Adverse fetal and neonatal effects have not been found in several studies documenting the use of cimetidine during labor and delivery.
Cimetidine Breastfeeding Warnings
Following oral administration of cimetidine 400 mg in one patient, the peak milk concentration was 5 mcg/mL. The milk to plasma ratio ranged from 3.04 to 3.57. Following a chronic dosing regimen in the same patient, cimetidine milk concentrations remained relatively constant, with milk to plasma ratios greater, although variable, than those noted in the single dose study. The authors suggest an active transport mechanism is involved.
Cimetidine is excreted into human milk. While the manufacturer recommends avoiding use during lactation, cimetidine is considered compatible with breast-feeding by the American Academy of Pediatrics.
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