Your Topical Medications Can Kill Your Dog

February 20, 2012

Most pet owners I run into as an emergency veterinarian assume that the hardest part of my job is euthanasia. While I don't take joy in that aspect of veterinary practice, I am happy that I am allowed to ease their suffering, and help them pass gently, without pain.

Telling someone that their healthy-looking, robust 9-month-old Boxer will almost certainly be dead within days, if not hours, with very little that can be done to stop it - now that sucks.

To be honest, I had never even heard of Efudex before last night, but the experience was so disturbing that I feel compelled to share it with you. It isn't "news" in the normal sense of this space, but I think it will provide a valuable lesson for all pet owners.

Many pet owners (including veterinarians) discount their own medication when considering what an animal may be exposed to, and over-the-counter medications "don't count" in many people's minds as "real" medications. But mix a few non-steroidals together, and you get some really fantastic bleeding ulcers.

Even worse, though, are the topical medications - they seem even less like "real medicine" than tablets do, and we all tend to forget about them. But topical hormones are dangerous! Estrogen creams can cause a pet's bone marrow to shut down, just by licking your treated arm (not to mention getting hold of the tube itself). See the mypetED post on topical hormones here.

But, after almost 19 years in practice, I can say that I've met the Devil, and he lives in a 40 gm tube. Efudex, otherwise known as 5-fluorouracil, or 5-FU (don't say it) is a potent cytotoxic (cell-killing) drug, used to treat proliferative skin disorders in people, including some forms of skin cancer and psoriasis.

If you have basal cell carcinoma, this may be an important medication for you to use. But please, please do not allow any contact with your pets (dogs or cats) and your medicated skin, and make sure that the medication itself is kept locked away.

This poor Boxer puppy. Sweet, well-trained, well-cared-for, and well-loved.

Fluorouracil is considered extremely toxic at a dose of less than 7 mg/kg (so, in this 25 kg dog, 175 mg would probably be fatal - in smaller dogs, just licking the treated skin would do it). He ate half of a 40 gm tube of 5% 5-FU. You math nerds have already figured out that the tube has 2 grams, or 2000 mg, of 5-FU. He chewed up the tube from underneath the sink, and his owner didn't realize it's toxicity until he started vomiting a couple of hours later. But the delay didn't matter. I knew, after reading about the drug, and consulting with the toxicologist at 3 am, that this guy had less than a 1% chance of being alive in 2 weeks.

I won't go into the gory details about exactly what is going to happen to him. Just know that the hardest thing I do isn't euthanizing an old, sick dog, easing her transition from this world to the next. It's looking at an owner, and telling her there is virtually no hope for him to survive, because her medication is going to tear him apart.

So please, for your sake, and your pet's sake, take an inventory of your own medication, and keep a list. Go over the list with your veterinarian, and make sure you know what's what. And, if you have Baby Boomer parents like I do, and they have pets, help them do the same thing.

Let's make this guy the last victim of Efudex.

Michael LoSasso, DVM