Is gentamicin (aminoglycoside antibiotic) eye drop safe to use in a 24-week pregnant woman?

Safety of Gentamicin Eye Drops in a 24-Week Pregnant Woman

Gentamicin eye drops can be used in a 24-week pregnant woman when clinically indicated, as topical ophthalmic gentamicin has minimal systemic absorption and the FDA pregnancy category C designation indicates potential benefits may outweigh risks.

Safety Profile of Gentamicin During Pregnancy

FDA Classification and General Safety

• Gentamicin is classified as Pregnancy Category C, indicating that animal studies have shown adverse effects on the fetus, but there are no adequate well-controlled studies in pregnant women 1
• The FDA label states gentamicin should be used during pregnancy "only if the potential benefit justifies the potential risk to the fetus" 1

Systemic vs. Topical Administration

• Topical ophthalmic preparations have significantly less systemic absorption compared to intravenous or intramuscular administration 2
• Systemic gentamicin (when used parenterally) has been associated with potential risks:
  • Animal studies showed depression of body weights, kidney weights, and median glomerular counts in newborn rats when administered systemically to pregnant rats in high doses 1
  • These effects were seen at approximately 500 times the maximum recommended ophthalmic human dose 1

Evidence Supporting Safety

• A study examining gentamicin use in pregnancy found no cases of hearing loss in infants exposed to gentamicin in utero, even with systemic administration 3
• This study reviewed 52 cases of pregnant women who received gentamicin (primarily for pyelonephritis and chorioamnionitis), and all infants who underwent hearing tests passed, with 89% passing on initial screening 3

Clinical Considerations for Use

Benefit-Risk Assessment

• The potential benefits of treating ocular infections during pregnancy must be weighed against theoretical risks 4
• Untreated ocular infections can potentially progress to more serious conditions that might require systemic antibiotics, which would result in higher fetal exposure 2

Monitoring Recommendations

• If gentamicin eye drops are used, proper administration technique is important to minimize systemic absorption:
  • Apply gentle pressure to the lacrimal sac during and immediately after instillation to decrease systemic absorption 2
  • Avoid touching the tip of the container to the eye to prevent contamination 1

Alternative Options

• If there are concerns about gentamicin use, consider that:
  • Erythromycin ophthalmic preparations may be safer options during pregnancy 2
  • Beta-blockers tend to be used during pregnancy for conditions like glaucoma because of long-term experience with this drug class 5

Special Considerations

Duration of Treatment

• Prolonged use of topical antibiotics may give rise to overgrowth of nonsusceptible microorganisms, including fungi 1
• Bacterial resistance to gentamicin may develop with extended use 1
• Treatment should be limited to the shortest duration necessary to resolve the infection 4

Monitoring for Adverse Effects

• If purulent discharge, inflammation, or pain becomes aggravated, the patient should discontinue use and consult a physician 1
• If irritation or hypersensitivity to any component develops, the medication should be discontinued 1

In conclusion, while gentamicin eye drops carry a theoretical risk during pregnancy, the minimal systemic absorption from topical ophthalmic application and the absence of documented adverse fetal outcomes from topical use suggest that short-term use for treating ocular infections in a 24-week pregnant woman is reasonable when clinically indicated.