Drugs can be harmful for the fetus at any time during the pregnancy. One should always have this at the back of their mind when prescribing for a women of childbearing age.

Drugs may produce congenital malformations (teretogenesis). The most risky period is from the 3rd to the 11th week of pregnancy.

The growth and functional development of the fetus may be affected during the second and third trimesters. The drugs can also have toxic effects on the fetal tissues.

Drugs can also have adverse effects on labour or on the neonate, if given before term or during labour.

Because most of the drugs we give to the mother usually crosses the placenta. The benefit of the drug must outweigh the risk before the drug is administered.

History of the use of drugs for bacterial infections in pregnancy:

As early as in 1946 sulfonamides were used by Haseltine and Thelen as a prophylactic agent for cesarean section. In 1959 Keetle and Plass used penicillin as prophylactic agent.

Therefore antibiotics have been used for decades in obstetrics. Numerous studies have proved their usefulness and safety.

Guidelines for drug therapy in pregnancy:

i)The antibiotic usage in pregnancy must follow the general principles of medication during pregnancy. The benefit of the drug must outweigh the risk .

ii)To limit the emergence of resistant organisms, the narrowest spectrum of antibiotics should be chosen.

iii)One has to bear in mind that pregnancy leads to expansion of maternal blood volume, increased glomerular filtration rate, increased hepatic metabolism and sequestration of drug in the fetal compartment.The maternal drug levels are lower (10-50%) in late pregnancy and immediate postpartum than in the non-pregnant woman.

iv) All antibiotics cross the placenta and enter the fetal circulation.

v) There is greater transfer of drugs that are minimally protein bound.

vi)Greater transfer of drugs across the placenta takes place with advancing gestational age.

Grouping of Drugs according to breast milk secretion:

Group I: Drugs do not enter the breast milk.

Group II: Drugs enter the breast milk but do not cause harmful effects on the fetus at therapeutic doses.

Group III: Drugs enter the breast milk and exert harmful effect on fetus even in therapeutic doses.

Group IV: No information regarding the secretion of the drug in breast milk.

Most antibiotics are excreted into breast milk to varying degrees, but adverse effects on the neonate are rarely encountered.

Classification of Drugs for Antibiotic safety in Pregnancy.

Category

A: No fetal risk- It is proven safe during pregnancy.

B: Fetal risk not proven in animals/human studies.

The Swedish catalog of registered pharmaceutical specialties categories this into three subgroups again:

B1 : Animal reproduction studies does not show any harmful effect.

B2: Reproduction toxicological studies are incomplete.

B3: Reproduction toxicological studies show deleterious effect on the fetus or reproduction or both.

C: Fetal risk is unknown or adequate human studies have been done.

D:Some evidence of fetal risk may be necessary to use the drug in pregnancy.

Most of the antimicrobial drugs approved for general use in pregnancy are are safe (Not teratogenic) except for tetracyclines and rifampicin.

The entire group of quinolones (eg ciprofloxacin), is contraindicated in pregnancy because of reports of arthropathy with their use in young animals.

The cephalosporins are considered safe to use during pregnancy.

It must be emphasized that for many drugs (eg acyclovir, azithromycin and newer cephalosporins) ,no theoretical or known risks exists to the fetus.There are numerous reports of uneventful use during pregnancy.However conrtolled trials during pregnancy are not sufficient enough to determine safety of these agents with certainty.

Sulfonamides and co-trimoxazole have been shown to be teratogenic( can give rise to birth defects) in animals .

Table of Antibiotics commonly used in pregnancy

Considered safe:

Aminopenicillines

Cephalosporins( 1st, 2nd, 3rd and 4th generation)

Erythromycin

Clindamycin

Probable safe use with lactation:

Azithromicin

Metronidazole

Nitrofurantoin

Contraindicated:

Doxycycline

References:

Page 741. Appendix 4. British National Formulary (BNF) 48. September 2004.

Pages 126 to 129, Chapter 16. Chemotherapy for Bacterial Infections during Pregnancy by Atul Munshi and Sujal Munshi. Medical Disorders in Pregnancy -an update. Ist edition .Edited by Hiralal Konar and Pralhad Kushtagi. A publication of the Federation of Obstetrics and Gynaecological Societies of India.

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