Is Polytrim (trimethoprim) safe to use for a patient with a known allergy to Bactrim (sulfamethoxazole and trimethoprim) for treating pink eye?

Polytrim is Safe for Patients with Bactrim Allergy

Polytrim (trimethoprim-polymyxin B) can be safely used in patients with Bactrim allergy because the allergic reaction to Bactrim is almost always due to the sulfonamide component (sulfamethoxazole), not the trimethoprim. 1

Understanding the Allergy Components

The critical distinction here is identifying which component of Bactrim caused the allergic reaction:

• Bactrim contains two drugs: sulfamethoxazole (a sulfonamide) AND trimethoprim 2
• Polytrim contains: trimethoprim AND polymyxin B (no sulfonamide) 3, 4
• The sulfonamide component is responsible for the vast majority of allergic reactions to Bactrim, not the trimethoprim 1
• No cross-reactivity exists between sulfonamides and other drug classes, including trimethoprim 1

Clinical Evidence Supporting Safety

Polytrim has been extensively studied and proven effective for bacterial conjunctivitis without sulfonamide-related reactions:

• A multicenter trial of 230 patients demonstrated that trimethoprim-polymyxin B was highly effective for presumptive bacterial conjunctivitis with very few adverse reactions 3
• Direct comparison studies showed that adding sulfacetamide to trimethoprim-polymyxin B produced identical clinical results, confirming the sulfa component is unnecessary 4
• The combination was significantly more effective than chloramphenicol (P = 0.03) in reducing signs and symptoms 3

Important Caveats About Trimethoprim Allergy

While rare, you must verify the patient's reaction was truly to the sulfonamide component:

• Anaphylactic reactions to trimethoprim alone have been documented, though they are uncommon 5
• If the patient had a severe reaction (anaphylaxis, Stevens-Johnson syndrome, angioedema), document the specific details and timing of the original reaction 1
• Reactions witnessed by healthcare providers are more reliable indicators of true allergy 1
• One case report documented erythema multiforme after topical sulfacetamide in a patient who had previously tolerated oral trimethoprim-sulfamethoxazole, confirming the sulfonamide was the culprit 6

Alternative Options if Trimethoprim Cannot Be Used

If there is documented evidence that trimethoprim itself caused the reaction (extremely rare), consider these alternatives for bacterial conjunctivitis:

• Fluoroquinolones: moxifloxacin or ciprofloxacin ophthalmic 1
• Aminoglycosides: gentamicin or tobramycin ophthalmic 1
• Macrolides: erythromycin or azithromycin ophthalmic 1

Documentation Requirements

Document in the medical record:

• The specific reaction to Bactrim (rash, anaphylaxis, timing, severity) 1
• Clinical reasoning for using Polytrim despite Bactrim allergy 1
• That the sulfonamide component, not trimethoprim, is the likely allergen 1