[Antibiotics and pregnancy]

Antibiotherapy during pregnancy has to be adapted according two factors: pregnancy related pharmacodynamic changes and potentially negative side effects for the developing foetus of some antibiotics. Pregnancy induce a weight gain, an increase of intravascular volume, of glomerular filtration, and of hepatic metabolism. The foetoplacental unit create a new volume in which antibiotics penetrates increasingly during gestation. As a consequence, during pregnancy, maternal plasmatic levels of antibiotics reaches values 10-50% under the ranges observed with the same dosages administered to non pregnant women. Tobramycin of which clearance diminish during pregnancy is the only exception for this rule. In term pregnancy, placental transfer of antibiotics is very high, except for macrolides. Thalidomide, a well-known responsible of phocomely, is still used in the treatment of leprae. No other antibiotic as a well demonstrated teratogenic effect in human foetuses. Nevertheless, tetracyclin use in pregnancy must be avoided according a high risk of enamel dysplasia, with brownish discoloration of deciduous teeth. No teratogenic effect has been recorded for betalactams and for erythromycin, the first choice antibiotics during pregnancy. Some antibiotherapy are specific of obstetrical conditions. Antibiotics interferes with estrogens metabolism, inducing a fall in circulating level of estriol.