We as veterinarians and you as producers run into many questions in our careers regarding whether we can or cannot use expired medications in cattle production.
Veterinary clinics cannot sell product that has been expired, so if you see that a product has expired, simply take it back as a mistake has been made.
In production animals we can, in some instances, use some common sense if you have recently expired products. Firstly, expiry dates are put on because the product has only been tested for that length of time after manufacture to ensure complete efficacy.
Vaccines are the least stable and often have the shortest expiry dates. They are the ones that need refrigeration, just like Pfizer’s COVID-19 vaccines, that need storage at -80 C. We need to make sure to store, handle and rehydrate the vaccines according to label instructions and maintain the chain of refrigeration for good efficacy regardless of the expiry dates.
It should be noted that when trials are done, there is a certain amount of antigen that is tested. When they manufacture the vaccines, the antigen is about doubled — the reason being so efficacy can be maintained at least as good as the trial results right up to the expiry date.
With vaccines being a biologic there is some degradation over time. The degradation is going to be some sort of line downwards. This doesn’t mean that the day after the expiry date efficacy drops to zero; it means it may start to drop below what is considered the protective dose. Lots of factors may accelerate this degradation such as storage (freezing is usually the kiss of destruction). In a multivalent vaccine, some of the antigens may degrade quicker than others.
Keep in mind the expiry dates that you see are the length of time that the product was licensed for. It may be effective after that, but we have no way of knowing. In the past, companies (if they had in stock a large amount of soon-to-be expired product) could have it tested for efficacy and actually relabelled or restickered. I don’t see that anymore and don’t know if it’s allowed as regulations are very tight.
It is best to try and have tight control on drug inventory either at the drug centre, the veterinary clinic, and lastly at the producer’s place. Most times when you buy product, especially vaccines, ideally you want to get it just prior to using it but ensure for leftover that the expiry is at least good until the next time you use it.
Companies do have a return policy from the veterinary clinics so they try and ensure they always have good expiry dates. When clinics buy from the large drug centre in Edmonton or even directly from the manufacturer, expiry dates are included on the invoice so it can be tracked. I do wish that manufacturers in the pharmaceutical industry had a quick mechanism when there is overproduction that extending the expiry dates could be extended with testing. This creates lots of waste or slippage when products need to be discarded and disposed off once expiry dates are exceeded.
Expiry dates on antimicrobials and things such as dewormers or implants are generally much longer as they are more stable molecules/products. There seems to be a maximum expiry date allowable. You may have noticed when you pick up your own prescription of pills that generally the expiry date is one year. This way they take the cautious ground knowing if a year has gone by you should be done the medication or have got another prescription. Even though products in production medicine may have a lot longer expiry date, in reality they are only allowed to make the expiry date so long.
There are some expiry dates that are a bit ambiguous.
Take, for example, implants will have an expiry date and that means time is allowed for the implant to work. For example, the X series of Revalor implants may release hormones up to 230 days, so the implant if given right at the expiry date, it will still be paying out for 230 days. These products are extremely safe and extremely stable the way they have been formulated so unless inventory control goes awry, expired implants should not be commonplace.
With antimicrobials and dewormers, if you come across expired product talk to your veterinarian as they may know the stability and subsequent efficacy of slightly expired product and whether you will still get good results. Depending on the seriousness of what you are treating is inversely proportional to whether you trust to use an expired product. I definitely would shy away from and dispose of partially used bottles or ones that have discolouration or sediment in them.
There are times when replacement product cannot be found immediately, so it may be worth taking a chance — but again, talk to your clinic/veterinarian. By keeping close control of inventory and the clinic watching expiry dates, as well as purchasing appropriate-size doses, we can eliminate the big waste of disposing of lots of expired products. We usually need to trust the efficacy of the products we use, hence the need to monitor expiry dates. Adverse events or lack of efficacy work-ups will be frowned upon if it is found expired products have been used.