Is Polytrim (polymyxin B and trimethoprim) safe to use during pregnancy?

Polytrim (Polymyxin B-Trimethoprim) Safety in Pregnancy

Polytrim ophthalmic solution can be used during pregnancy when clinically necessary, as the systemic absorption from topical ophthalmic administration is minimal and unlikely to cause fetal harm, though trimethoprim carries theoretical risks related to folate metabolism that warrant folic acid supplementation. 1

Risk Classification and Evidence Base

• The FDA classifies trimethoprim as Pregnancy Category C, meaning animal studies have shown teratogenic effects at high oral doses (40 times human dose in rats), but adequate human studies are lacking 1
• Polymyxin B has not been adequately studied in pregnancy, but animal reproduction studies have not been conducted 1
• Critical distinction: Topical ophthalmic use results in negligible systemic absorption compared to oral administration, fundamentally changing the risk-benefit calculation 2

Systemic vs. Topical Administration: A Key Distinction

• Polymyxin B has no corneal penetrating powers and remains at the ocular surface, resulting in minimal to no systemic absorption 2
• Erythromycin and polymyxin B are considered "probably okay to use as topical applications in pregnant women and nursing mothers" based on their pharmacokinetic profiles 2
• The concerns about trimethoprim-sulfamethoxazole in pregnancy (increased spontaneous abortion risk with adjusted OR 2.94, neural tube defects, kernicterus) are based on oral systemic therapy, not topical ophthalmic use 3, 4

Clinical Recommendations by Trimester

First Trimester

• Can be used for bacterial conjunctivitis when indicated, as topical absorption is minimal 1, 2
• Ensure all women of childbearing potential receive at least 400 μg daily folic acid supplementation to mitigate theoretical antifolate effects 3

Second and Third Trimesters

• Safe to use with even greater confidence, as the period of organogenesis has passed 3
• Continue folic acid supplementation throughout pregnancy 3

Near Term

• While systemic TMP-SMX is contraindicated near term due to kernicterus risk, topical ophthalmic Polytrim does not achieve sufficient systemic levels to pose this risk 5, 3

Practical Treatment Algorithm

For pregnant women with bacterial conjunctivitis:

1. First-line approach: Polytrim ophthalmic solution is appropriate and effective 6, 7

   • Clinical cure rates of 95-96% demonstrated in controlled trials 7
   • Effective against common pathogens including Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis 7

2. Dosing: Standard ophthalmic dosing (typically 1-2 drops every 4-6 hours) 6

3. Duration: 7-10 days for complete bacterial eradication 7

4. Concurrent management: Ensure patient is taking prenatal vitamins with adequate folic acid (≥400 μg daily) 3

Alternative Considerations

• If patient has concerns about any trimethoprim exposure, erythromycin ophthalmic ointment is an alternative with established safety in pregnancy 2
• Moxifloxacin shows equivalent efficacy but is more expensive and offers no safety advantage over Polytrim for topical use 7

Common Pitfalls to Avoid

• Do not extrapolate oral TMP-SMX pregnancy risks to topical ophthalmic Polytrim - the systemic absorption profiles are fundamentally different 2
• Do not withhold effective treatment for bacterial conjunctivitis due to misplaced concerns - untreated maternal infections can have their own adverse effects 3
• Do not forget folic acid supplementation - this simple intervention addresses the theoretical antifolate concern 3
• Do not contaminate the applicator tip during administration to maintain sterility 1

Monitoring and Follow-up

• Monitor for treatment response within 4-6 days 7
• If symptoms persist or worsen, re-evaluate for resistant organisms or alternative diagnoses 1
• No specific fetal monitoring is required beyond routine prenatal care when using topical Polytrim 1