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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.
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.
References
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
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.