Tuesday, September 17, 2013

Why dog flea products should not be used on cats

Spot-on flea products must be used carefully. ALWAYS read the label.
“The only thing necessary for the triumph of evil is for good men to do nothing.” – Edmund Bourke.

Permethrin toxicity is common in cats but strikingly underreported in the published literature. It is unlikely that pet owners or veterinarians fully comprehend the enormity of the problem. My training certainly didn’t prepare me.

During my first year as a new graduate I was on call when a nine-year-old male neutered domestic shorthair was presented by two young boys – 15 and 18 years old respectively. The boys, concerned the cat was bothered by fleas, asked their parents for money to purchase some treatment. When they got to the supermarket they had just enough money for a spot-on product intended for small to medium dogs – not the slightly dearer product intended for cats.

The product contained permethrin, a synthetic pyrethroid that is metabolised very differently in dogs than cats. 

Not seeing the warning (which was in fine print, buried in the extensive information on the packet), they applied the spot-on product to Cuddles. Several hours later they noted Cuddles was acting strangely – frightened, scared, and twitchy. Their regular vet wasn’t answering, and they didn’t have a car to drive to the 24-hour-referral centre. Their parents didn’t volunteer. So they arrived on our doorstep, having finally read the packet label and bathed the cat twice in an effort to decontaminate the fur.

On examination the cat was wet (consistent with bathing), drooling a little, and had dilated pupils. Otherwise it seemed fine. The boys reported no exposure to other toxins, no seizures or loss of consciousness, no history of loss of bowel or bladder function and no vomiting. The only issue was that the cat had been treated with permethrin. I knew this was toxic to cats, but didn’t appreciate how toxic. I sought advice in the most comprehensive textbook I could find: it suggested that “the overall prognosis is very favourable”, and treatment consisted of diazepam for seizures.

Well, this cat wasn’t seizuring. It had been rapidly decontaminated, and I didn’t want to risk inducing excitement by giving another bath. Since the cat was not seizuring and the prognosis was reportedly good in seizuring cats, I figured the prognosis for Cuddles was fair to good. I was very wrong.

I remember being touched by these boys’ concern for their cat. Thinking I was being overzealous, I admitted the cat, administered activated charcoal (to bind any toxin groomed from the fur) and gave a dose of diazepam to reduce the risk of seizure activity. I ran this by a colleague who agreed it was a good plan (she graduated in the same year I did, with the same instructors and same textbooks).

I left the clinic at 10pm that night. The cat was a little scared looking otherwise fine. I returned at 6am the following morning to find the cat in status epilepticus – intractable seizuring. Despite administration of numerous doses of medication the cat died later that morning.

My employer, a vet with some 20 years experience, said that those cats ALWAYS have a poor prognosis. I contacted the manufacturer of the product to report an adverse event. The receptionist took my call and said “oh, another one.”

So how could I reconcile the favourable prognosis given by the textbook? Because permethrin intoxication is massively under-reported. If a veterinarian in practice doesn’t take the time to report an adverse event, only the client and the vet know about it. Because many cats, as I learned from speaking with colleagues, don’t make it to the vet. Because a lot of owners cannot afford vet treatment – after all, many applied the dog product because it was cheaper than the cat product.

Every veterinarian I spoke to had treated cats for permethrin toxicity and the majority had treated or known of cats that did not make it.

An email I wrote to a colleague at the time expresses my frustration:

…I feel upset that an otherwise healthy cat died a particularly nasty death. Colleagues have since told me the cat would have been out of it but he was cooking his little brain in there and although I didn’t cause the suffering if I had known how bad it could have been I would have taken some further measures to prevent it.”

In an effort to make me feel better, a fellow vet friend said: “the clients killed the cat, you didn’t”.

Whilst the boys applied the toxin, I don’t believe it was their fault. How could they appreciate that cats are not small dogs – that they have a different way of metabolizing drugs that makes them exquisitely sensitive to this toxicity? They had a limited budget and bought a product that was within their means.

Aside from causing irritation and flea bite hypersensitivity, fleas are a health risk to cats and humans as they carry diseases like bartonella. These fleas were combed off a single (very anaemic) kitten.
Those kids were treating their healthy cat for fleas – they had no idea of the potential consequences. Even the warning, which stated plainly that the product should not be used on cats, did not explain that it could be harmful or fatal.

The more I read the more I learned. Diazepam, as it happened, was not the drug of choice – many permethrin-caused muscle fasiculations and seizures are refractory. It would have been prudent to refer the cat for 24 hour monitoring. And there was a HUGE discrepancy between the incidence of toxicity reported by my colleagues and that reported in the literature (ie there was not a single case reported to the Australian Veterinary Medicines and Pesticides Authority between January 1995 to May 2003.

I collaborated with colleagues and we surveyed Australian veterinarians about the incidence of permethrin related toxicities in cats. Most (81 per cent) of respondents had seen permethrin intoxication in a feline patient within the previous 2 years. In total there were 750 individual cases reported – with 166 deaths. Far from a favourable prognosis.

So: owners don’t always read labels, and veterinarians don’t always report adverse drug events (so the literature doesn’t always reflect reality).

But a product you buy from the supermarket shelf should be safe. It is my belief that permethrin spot-on products should not be available without point-of-sale advice. Detailed warnings need to be provided and they need to be understood. This is a preventable event, we have the potential to save lives, and permethrin intoxication is a veterinary health crisis for which we are all responsible. We owe it to Cuddles and all cats affected by this toxin to ensure that it is used responsibly.


Anon(2003) APVMA Report of Adverse Experiencs, January 1995 to May 2003 AS CITED IN Woo & Lunn 2004 – nb has since changed from http://www.apvma.gov.au/qa/aerp1995_2003.pdf

Dormon DC and Dye JA (2005) Chemical Toxicities. In Ettinger SJ and Feldman EC (eds) Textbook of Veterinary Internal Medicine, 6th edition. Elsevier Saunders, St Louis, p259.

Malik R, Ward MP, Seavers A, Fawcett A, Bell E, Govendir M and Page S (2010) Permethrin spot-on intoxication of cats – literature review and survey of veterinary practitioners in Australia. Journal of Feline Medicine and Surgery 12(1):5-14.

Woo A & Lunn P (2004) Permethrin toxicity in cats. Australian Veterinary Practitioner 34(4):148-151.