5-Fluorouracil Topical Cream (5FU or Fluorouracil 5%) is a topical drug formulation used to treat human skin cancers that is often fatal to dogs and cats if ingested. Dogs and cats are usually exposed to this cream accidentally (chewing on the tube or licking the cream off their humans after it has been applied), and the outcome of such exposure is often tragic. Signs of toxicity can start within 30 minutes, with rapid progression to seizures and death within six hours. The most common clinical signs of toxicity with this drug are vomiting, tremors, stumbling or lack of coordination, and seizures. Making matters worse, there are no known effective treatments for 5-FU toxicity in dogs and cats. An antidote exists for human patients, but the drug has not been used successfully to treat dogs and cats suffering from acute toxicities. Unfortunately, human health professionals and pharmacies are doing a very poor job of warning their patients about the dangers to pets, which means most of us are unaware of just how careful we should be with this medication.
After coming across an article about this product in one of my veterinary journals this week, I decided to check and see if we had any in our own medicine cabinet, though I was relatively certain we did not have any in our home. Sure enough though, I went through our bathroom drawers and found a nearly full tube! My wife had been prescribed the 5FU cream for a suspected basal cell carcinoma. The tube I found was appropriately labeled with all the human warnings but had no pet warnings at all. It was a 40 gram tube and as little as 56 milligrams can be fatal to a 50 pound dog! That means that little 40 gram tube I found contains enough of the drug to potentially be toxic to nearly 715 dogs! This is a much more toxic drug than I realized, which is alarming considering how commonly it is being prescribed without adequate warnings.
Because the dangers of this drug for our pets are not widely known, I wanted to reach out in this way with a caution to keep this drug away from your treasured four legged friends. This is not a mild mannered cream you put on your skin. It can be fatal to dogs and cats in very small doses and should be stored and used with extreme caution. We recommend that you check out your bathroom drawers and see if you have any in your home, and if you do, put it in a safe place where your pets cannot get to it. If you are currently using this cream, be careful not to allow your pets to lick the area that has had the cream applied.
Thanks for reading and as always, feel free to reach out with any questions or concerns!