Q. I often have prescription flunixin meglumine (Banamine) paste, phenylbutazone (Bute), and sulfamethoxazole and trimethoprim (SMZ-TPM) on hand for my horses in case of emergency. I always consult my veterinarian before giving my horse prescription drugs. Often, though, the drugs I have on hand expire before I finish using them. Is it okay to administer these expired drugs to my horse, or do I need to contact my veterinarian about replacing them?

—via email

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A. Similar to the food you buy in the grocery store, drugs break down over time and are no longer effective. Drug manufacturers are required to perform studies to assess how long their products can safely be used and are required to provide an expiration date so that consumers know how long they can rely upon the product. It is difficult to predict how much of a product you need to have on hand, and everyone hates throwing away unused products, but for the safety of your horse it is best to keep only a small amount of these products on hand and to replace them when they expire.