Polymyxin B/TrimethoprimPolymyxin B sulfate / Trimethoprim

About Polymyxin B/Trimethoprim

The drop combines two antibiotics. Polymyxin B kills gram-negative bacteria, especially Pseudomonas aeruginosa, and trimethoprim is active against a wide range of aerobic gram-positive and gram-negative eye pathogens, so together they cover the organisms that usually cause pink eye and eyelid infections. The label approves the solution for surface bacterial eye infections caused by susceptible strains, including acute bacterial conjunctivitis and blepharoconjunctivitis. It is not indicated for the eye infection of newborns (ophthalmia neonatorum), and safety and effectiveness in children under 2 months have not been established. For mild to moderate infections the dose is one drop in the affected eye or eyes every three hours, to a maximum of six doses a day, for 7 to 10 days.

There is no boxed warning. The solution must not be used by anyone allergic to polymyxin B, trimethoprim or any other ingredient, and if a sensitivity reaction develops it is stopped. It is for the eye only and is never injected into the eye. As with any antibiotic, prolonged use can let nonsusceptible organisms, including fungi, overgrow, and the label says not to wear contact lenses while there are signs of a bacterial eye infection. The most common side effect is local irritation: more redness, burning, stinging or itching, which can appear on instillation, within the first two days or with longer use. Hypersensitivity reactions with eyelid swelling, itching, redness, tearing or a rash around the eye have been reported, and the label revised in August 2025 adds that Stevens-Johnson syndrome, toxic epidermal necrolysis and anaphylaxis have been reported. The label says to use it in pregnancy only if the potential benefit justifies the potential risk to the baby.

What is distinctive is that this is a short, self-limited course from a single small bottle. The solution comes in a 10 mL dropper bottle, preserved with benzalkonium chloride, and is stored at 15 to 25 degrees C (59 to 77 degrees F) and protected from light. Because bacterial conjunctivitis spreads easily, MedlinePlus advises washing the hands often, keeping the dropper tip away from the eye, fingers, face and any surface, and replacing or cleaning eye makeup and contact lenses that touched the infected eye. The Polytrim brand label, distributed by Allergan, was revised in August 2025, but the brand product itself is listed as discontinued in the Orange Book, so the drop is dispensed as a generic. Polymyxin B and trimethoprim drops are not a controlled substance.

Taking Polymyxin B/Trimethoprim

How to take it

Wash your hands, tilt your head back, pull the lower lid down to make a pocket and squeeze one drop in without letting the tip touch your eye, fingers or any surface. Close the eye and press on the inner corner for two to three minutes, then recap the bottle without wiping or rinsing the tip. Use it every three hours, up to six times a day, for the full 7 to 10 days the prescriber ordered.

If you miss a dose

Use it as soon as you remember, unless it is almost time for the next dose; then skip the missed dose. Do not use a double dose.

Storage

In the original bottle, tightly closed, at room temperature (15 to 25 degrees C, 59 to 77 degrees F), protected from light and away from heat and moisture, out of reach of children.

Interactions to know about

The label has no drug interactions section. Tell the pharmacist about any other eye drops you use so they can be spaced apart, and do not wear contact lenses while the infection is being treated.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Polymyxin B/Trimethoprim differs from pharmacy to pharmacy

The drop is an old generic that most pharmacies stock, so quotes differ mainly with the maker the pharmacy buys from and whether the drug is on a flat-price generic list. With the brand discontinued, every quote is for a generic bottle, and pharmacies that buy from different makers quote differently for the same 10 mL.

One 10 mL bottle is a whole course, so the quote is for a single small item and the dispensing fee is a large share of it.

Ways to pay less for Polymyxin B/Trimethoprim without insurance

• Ask the prescriber to write the generic name and allow substitution.
• Compare more than one pharmacy, and ask whether the drop is on a flat-price generic list, since a short course is often included.
• Ask the prescriber whether the whole household needs to be checked when pink eye is spreading, so that one visit covers everyone who needs a prescription.
• Start the drops promptly and finish the full course, so you do not need a second prescription for the same infection.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Polymyxin B/Trimethoprim

1. 1.How do I space six doses a day, and do I need to wake up at night for my drops?
2. 2.When can I wear my contact lenses again, and should I throw away the pair I was wearing?
3. 3.What should I do if my eye gets redder or starts stinging after the drops?
4. 4.Is it safe to use these drops while I am pregnant or breastfeeding?

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