Unopened erythromycin ophthalmic ointment is good until the expiration date printed on the tube, which is typically two to three years from the date of manufacture. Once you open it, most eye doctors recommend discarding the tube after 28 days, regardless of how much ointment remains.
Unopened vs. Opened Shelf Life
The expiration date stamped on erythromycin ophthalmic ointment is based on stability testing the manufacturer performs under controlled conditions. You’ll find this date on the crimped end of the metal tube or on the outer packaging. As long as the tube stays sealed and stored properly, the ointment retains its potency and sterility through that date.
Once you break the seal, the math changes entirely. Every time the tube tip touches your eye, eyelid, or fingers, bacteria can work their way inside. The ointment base doesn’t contain strong preservatives designed for long-term repeated use, so contamination risk climbs quickly. The general guideline from ophthalmologists is to throw the tube away 28 days after first opening, even if there’s plenty of ointment left and the printed expiration date is months away.
How to Store It Properly
The official storage range listed on the FDA’s DailyMed labeling is 15°C to 25°C (59°F to 77°F). Cleveland Clinic gives a slightly wider window of 15°C to 30°C (59°F to 86°F). In practical terms, a room-temperature drawer or medicine cabinet works fine. Keep it away from direct sunlight and heat sources like a bathroom radiator or a car dashboard in summer.
Do not freeze the ointment. Freezing can alter the consistency of the petrolatum base, causing the active ingredient to distribute unevenly. If the tube has been frozen, it’s safest to replace it.
Signs the Ointment Has Gone Bad
Even before the 28-day or printed expiration window, the ointment can degrade if it’s been stored incorrectly or contaminated. Watch for these changes:
- Color shift: Fresh ointment is a pale, slightly yellowish, translucent gel. Any darkening or brown discoloration suggests chemical breakdown.
- Texture changes: The ointment should be smooth and uniform. If it looks grainy, separated, or dried out at the tip, it may no longer distribute the antibiotic evenly.
- Unusual smell: A rancid or noticeably different odor indicates the base has degraded.
If you notice any of these, discard the tube regardless of dates.
Why Using Expired Ointment Is Risky
The concern with expired or old ophthalmic ointment isn’t just reduced effectiveness. Two things happen as the product ages or sits open. First, the antibiotic itself loses potency, meaning it may not clear the infection you’re treating. An undertreated bacterial eye infection can worsen or become harder to treat later. Second, and more importantly for opened tubes, bacterial contamination inside the tube can introduce new pathogens directly onto your eye. Applying contaminated ointment to an already irritated or infected eye can make things significantly worse.
Eyes are especially vulnerable because the moist, warm tissue of the conjunctiva is an ideal environment for bacteria to multiply. This is why ophthalmic products have stricter discard timelines than, say, a skin ointment with the same active ingredient.
Typical Treatment Length
Most prescribed courses of erythromycin ophthalmic ointment for bacterial conjunctivitis run about 7 to 10 days, with applications two to six times per day depending on the severity. That fits well within the 28-day post-opening window, so a single tube is usually enough for one course of treatment.
For newborns, the ointment is used just once, applied to both eyes within 24 hours of birth as a preventive measure against certain bacterial infections. In that context, shelf life matters primarily for the hospital or birthing center stocking the product, not for ongoing home use.
What to Do With Leftover Ointment
If you finish your prescribed course and still have ointment in the tube, don’t save it for a future eye infection. The 28-day clock is already ticking, and by the time you need it again, the tube will likely be past its safe window. Squeeze any remaining ointment into household trash (not down a drain) and discard the tube. A new prescription is inexpensive and ensures you’re starting with a sterile, fully potent product.