Polymyxin B / trimethoprim
Anti-infective · Rx
Trade namesPolytrim
Drug classAntibiotic, combination
StrengthPolymyxin B 10,000 U/mL + trimethoprim 0.1%
AvailabilityRx
Mechanism of actionPolymyxin B disrupts Gram-negative outer membranes; trimethoprim blocks folate synthesis (Gram-positive). Complementary spectrum, no aminoglycoside toxicity.
Indication / reason for useBacterial conjunctivitis and blepharoconjunctivitis, a good pediatric first choice.
Usual adult dosing1 drop every 3 h (max 6×/day) for 7-10 days.
PreservativeBAK 0.004%
Contact lensesNo lens wear during infection.
Common / important adverse effectsLocal irritation, lid itching/edema, hypersensitivity.
Contraindications & cautionsHypersensitivity to either component.
Pregnancy / lactationConsidered acceptable; commonly used in children.
Practice notesDoes not cover Pseudomonas well enough for a contact-lens ulcer.
Chair-side reference only. Dosing, contraindications and pregnancy guidance here are not exhaustive. Confirm against the current prescribing information and the patient’s full history before prescribing or advising.