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Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

Is It OK to Use Leftover Drugs If My Dog Gets Sick?

Updated: October 1st, 2018


Should you use those old prescriptions if your dog’s symptoms return? It turns out you probably shouldn’t. Dr. Stacy Branch, our resident pharmacologist, explains why.

prescription-drugs-leftoverIf you have some prescription drugs left from previous illnesses, you might be tempted to use those drugs with your dog again. But that’s not a good idea. Here’s why.

Expired Drugs Aren’t Safe

The main reason why you shouldn’t keep leftover drugs around is because they are unsafe. These unused or leftover drugs can be toxic to a child or pet who accidently swallows these drugs or is exposed to them in some other way.

You are right to want to help stop your dog’s suffering as soon as possible. Being able to quickly grab pills that you used for your dog before is tempting and can even seem helpful.

Also, the rising cost of drugs, and in particular those to treat cancer, can be very hard on your budget. So you may also believe that using some leftover drugs will help you better deal with veterinary medical costs.

It is wonderful that you want to help your dog feel and live better, but there are actually very good reasons to avoid the use of leftover drugs in case your dog gets sick again:

  • Some drugs are only available by prescription to help prevent their misuse. Drugs are prescribed for a specific patient with a specific illness. The instructions for the use of prescription drugs (the ones that come with the bottle) are so particular because of the chance that a drug could be mistakenly misused and cause harm. Many drugs, including those used to treat cancer, are quite toxic and can be very dangerous if given to your dog in the wrong way or for the wrong reasons.
  • Sometimes people keep their dog’s drugs past the expiration date. Prescribed and over-the-counter drugs have expiration dates because people sometimes fail to store the drugs properly. For instance, we know that some foods will go bad if not stored in the refrigerator or are left out at room temperature for too long. Drugs also have to be stored in a way to keep them safe and useful. Since the drug makers have no way of knowing if someone will follow the storage instructions, they put expiration dates that take any wrong handling into account such as letting moisture in pill bottles or leaving the drugs on a hot window sill.

What Helped Once Might Not Help Now

What about drugs that are not expired? As mentioned, drugs are prescribed for a specific patient with a specific illness. Many people think that they can just give their dog his unused or old drug stash if they see signs of an illness that the dog had before.

On the surface, this seems like a good idea, especially when you’re in a state of panic and not sure what to do.

The danger is that the vast majority of signs and symptoms can be due to a number of different illnesses. So you won’t really know if your dog’s symptoms are due to the illness he had before.

For example, it is very common for dogs with lymphoma located in the chest area to experience breathing problems. Many veterinary doctors prescribe a combination of different drugs to treat this form of cancer in dogs. What if you notice that your dog’s breathing greatly improved with one of the tablets prescribed, but later the breathing problems begin to develop again? It may be tempting to just give the drugs again instead of letting a veterinarian examine the dog first.

Even though you want the best for your dog, it is actually dangerous to give the leftover drugs as in this lymphoma case.

For example, prednisone is often part of the drug combination given for canine lymphoma. Although this drug has many benefits for dogs with this type of cancer, it must be used under your veterinarian’s care and recommendations. The wrong use of this drug can cause harm rather than help your dog during a crisis.

In addition, giving this prednisone yourself may make it hard for the veterinarian to uncover the actual cause of the dog’s breathing problem because this drug is very powerful at relieving this type of symptom.

Another thing is that overuse of this drug can cause a number of health problems such as infections due to its ability to the body’s defenses. Even though your intentions to help your dog are excellent, you may actually cause more problems for your dog without meaning to.

Bottom Line: Ditch the Drug When It’s Usefulness Is Past

Therefore, the reasons why previously-prescribed drugs should not be kept on hand are:

  1. Old, leftover drugs can be unsafe.
  2. Old drugs may become useless after a period of time.
  3. Old drugs may lead to health problems if given to dogs after a period of time.
  4. Using these may prevent your veterinarian from finding the real cause of your dog’s illness, and this will delay the best treatment.
  5. Using these for the wrong reason can put your dog’s health in more danger.

Although it may seem handy to keep leftover drugs in case your dog has another illness, the possible unhealthy results outweigh any possible good. The Food and Drug Administration has a website with suggestions on how to safely get rid of unused drugs:

It’s better to find out the specific cause of any new or returning illness from your veterinarian. This will allow the quickest start of the best treatment to get your dog back to a happy and healthy state.

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