Antibacterial agents in pregnancy

Except for topical, nonabsorbable agents, any antibiotic chosen for use in pregnancy exposes the fetus as well as the mother to its effects. Therefore, initiation of antimicrobial therapy must be based on clear-cut necessity. Because the physiology of the maternal-fetal unit is complex and ethical consideration of potential fetal harm is pre-eminent, data on safety are derived from animal studies, incidental observations on individual women treated with an agent, or longitudinal tracing of groups of women who required treatment with a particular antimicrobial regimen. Consequently, a rating of absolute safety in pregnancy has never been assigned to any currently available antimicrobial agent. Decades of clinical experience with penicillins, cephalosporins, and erythromycins have documented the pharmacokinetics of these drugs in pregnant women as well as their overall safety for the fetus. These classes of drugs are those most favored for use in pregnancy for susceptible infections. Although aminoglycosides have known toxic effects on the fetus, they are safe to use if serum levels are carefully monitored in the mother. Agents in the quinolone, sulfonamide, and tetracycline categories should be avoided unless maternal necessity for their use justifies the exposure of the fetus to their toxicity. Both clinical and experimental data are very limited on the newer agents, such as the new macrolides, azithromycin and clarithromycin. The first-line agents for the treatment of TB (i.e., INH, rifampin, and ethambutol) are considered safe in pregnancy, but in the era of multidrug-resistant mycobacterial isolates, agents with known or suspected fetal toxicity may need to be used.