Antibioticos En El Embarazo

REVIEW ARTICLE

Antibiotics and Other Anti-infective Agents in Pregnancy and Lactation
Jennifer R. Niebyl, M.D.1

ABSTRACT

Serum levels of many drugs are lower in pregnancy compared with the nonpregnant state. Their renal clearance is higher and the maternal intravascular volume is expanded. Most antibiotics are safe for use in pregnancy and lactation. Tetracyclines cause fetal toothdiscoloration and inhibition of bone growth if used in the second and third trimesters. Aminoglycosides carry a small risk of fetal ototoxicity. Quinolones may cause arthropathies in children, and so are currently not recommended for use in pregnancy. Most drugs are secreted into breast milk in very small amounts, not enough to have any therapeutic effect. The only antibiotics which may be of concernin nursing infants are sulfonamides and quinolones, and possibly metronidazole.
KEYWORDS: Antibiotics, pregnancy, lactation

ntibiotics are widely used during pregnancy. Because of the potential for maternal and fetal side effects, they should be used only when the indication is clear and the risk:benefit ratio justifies their use. Pregnant patients should be warned that they are particularlysusceptible to yeast infections and may need therapy later with antifungal agents. Free samples of the newest drugs should not be given to women who might become pregnant, as there is often no human pregnancy information on the recently marketed drugs.

A

PENICILLINS The penicillins have a wide margin of safety and lack toxicity for both the pregnant woman and the fetus.1 There is no evidencethat penicillin or its derivatives are teratogenic. In the Collaborative Perinatal Project, 3546 mothers took penicillin derivatives in the first trimester of pregnancy, with no increased risk of anomalies.1 Of 86 women exposed to dicloxacillin in the first trimester, there was no increase in birth defects.2

American Journal of Perinatology, Volume 20, Number 8, 2003. Address forcorrespondence: Jennifer R. Niebyl, M.D., Professor and Head, Department of Obstetrics and Gynecology, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Iowa City, IA 52242; reprints not available from the author. 1Department of Obstetrics and Gynecology, University of Iowa Hospitals and Clinics, Iowa City, Iowa. Copyright © 2003 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY10001, USA. Tel: +1(212) 584-4662. 0735-1631, p;2003,20,08,405,414,ftx,en;ajp40370x.

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Pharmacology Several studies have revealed that the serum levels of the penicillins are lower and their renal clearance is higher throughout pregnancy when compared with the nonpregnant state.3 The increase in maternal renal function,because of an increase in both renal blood flow and glomerular filtration rate, results in a higher renal excretion of drugs. The expansion of the maternal intravascular volume during the late stages of pregnancy is another factor that affects antibiotic therapy. The transplacental passage of penicillin is by simple diffusion. Maternal administration of penicillins with high protein binding (e.g.,oxacillin, cloxacillin, dicloxacillin, and nafcillin) results in lower fetal tissue and amniotic fluid levels than the administration of poorly bound penicillins (e.g., penicillin G, ampicillin, and methicillin).4,5 The antibiotic is ultimately excreted in the fetal urine and thus into the amniotic fluid. At term maternal serum and amniotic fluid concentrations of penicillin G, ampicillin, andmethicillin are equal at 60 minutes after intravenous administration, representing rapid passage into the fetal circulation and amniotic fluid. Most penicillins are primarily excreted unchanged in the urine with only small amounts being inactivated in the liver. This requires reduction in dosage in patients with impaired renal function and increase in dosage during pregnancy.

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