Post-Expiration Date Dewormer Efficacy

Q. Is dewormer still good after its expiration date?

Lynn, Chicago, Ill.

A. Like all medications, dewormers have a limited shelf life, which is determined through drug stability testing. The expiration date on the label is the latest date for which the manufacturer can guarantee full product potency.

In addition to the expiration date, equal consideration should be given to proper product storage. If the dewormer was stored outside the recommended temperature range listed on the label (i.e., in the tack room or horse trailer where it could have gotten too hot or too cold) its drug stability will be negatively impacted, as well.

If an improperly stored or expired dewormer is utilized, the horse will likely not receive a sufficient dose and the product will fail to adequately address the horse’s parasite infection. Under-dosing is one of many factors than can contribute to parasite resistance.

Bottom line: If you want to be sure your horse is getting what you pay for, store all medical products within the label recommendations and administer prior to the expiration date.

About the Author

Nathan Voris, DVM, MBA

Nathan Voris, DVM, MBA, is a senior veterinarian with Zoetis’ equine technical services team. He completed his internship at Rood & Riddle Equine Hospital, in Lexington, Ky., and spent 10 years as an associate veterinarian with Equine Medical Services in Columbia, Mo. His primary interest areas include preventive equine medicine and social media.

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