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We know you sometimes have burning questions that can best be answered by a pharmacist. Our feature, Ask Your Pharmacist , seeks to address some of those issues. Send your questions to healthandwealth@jamaicaobserver.com.Question: Can I use an expired eye drop?Answer: Let us begin by defining what is an expired eye drop. Eye drops will generally be stamped with an expiry date one to two years after the date of manufacture. You should never use an eye drop after the expiry date. Once opened, though, the expiry date of the eye drop changes - the shelf life becomes three months from the date the seal is broken. That means you should throw away an opened eye drop after three months, even if it has not yet reached the stamped expiration date. Some manufacturers will recommend discarding eye drops within 28 days of opening, so be sure to read the instructions on the package insert. Once you open a bottle of eye drops, make a note of the date opened and count three months (or 28 days) from then to tell you when you have to discard the bottle. Some eye drops are single-use vials meant for one-time use. Once opened, these should be discarded within 24 hours. I know this sounds a bit confusing, but the expiry date of eye drops is not static, so we have to pay attention when using these products.Eye drops are made up of different chemical components. Like any other medicinal product, the components break down over time and lose their potency. Hence, after the expiry date, you might not get the desired effect from the medication. This will not prove beneficial for you as the patient, because the condition being treated will not be adequately remedied. This might lead the prescribing doctor to make faulty assumptions about the effectiveness of the treatment. He/she might, for example, decide to switch you to a more expensive eye drop in the hope that it will work better. We can help our doctors to be confident in their recommendation of products by ensuring that we are not using expired products which might be less effective at treating the ailment. In addition, the broken-down chemicals in expired eye drops can cause unwanted side effects such as irritation, inflammation, swelling, and redness. Again, this might lead us to incorrectly assume that the eye drop is not working well. Sometimes there are no physical clues as to the deterioration of the eye drop. However, sometimes you might notice that the eye drop changes colour or gets cloudy. If you notice any of these physical changes, it is important to throw out the eye drops right away.A lot of eye drops contain preservatives that keep the eye drop sterile. The preservatives also break down over time, making the eye drops prone to contamination by germs, especially if the eye drops have been opened. Exposure to oxygen can cause the drops to become unstable. This exposure, in itself, decreases the shelf life of the eye drop. In addition, the eye drops can become contaminated by normal bacteria that live on our eyeballs, lids, and lashes. Hence, it is important to prevent the dropper from touching these areas during application. Once an eye drop has been used, the cap should be replaced immediately to help preserve the sterility of the drop. If the tip of the dropper touches any dirty surface, it may become contaminated. If this happens, you might just have moved up the expiry date. It is best to discard the bottle right away if there is any risk of contamination. If the eye drop is contaminated, that puts you at risk of contracting an infection in the eye. Such an infection can have deleterious effects and can even lead to loss of vision.So, to answer the question, it is not safe to use expired eye drops. The important thing to note, however, is that once opened, the expiry date of an eye drop changes from the stamped date to three months after opening or the point at which it gets contaminated by touching a dirty surface.Novia Jerry Stewart, MSc, RPh, is a pharmacist who specialises in ophthalmic care. She may be contacted at novia_jerry@yahoo.com.