Permethrin and Cats Don't Mix — Call for Action

These data are shocking, not just because of the high numbers of cats affected and the high mortality rates, but because this problem is and should be avoidable.

In this issue of JFMS, we have an important paper from Professor Richard Malik and colleagues highlighting the significance of permethrin spot-on (PSO) poisoning in cats in Australia. ¹ This study presents valuable data and recommendations for tackling what has become a major problem in feline medicine.

In 1999, Meyer reported 11 cases of permethrin toxicity in cats in the USA following application of products containing 45–65% permethrin, four of which died. ² The report also highlighted an additional case of secondary poisoning in a cat sharing the environment with two dogs that were treated. A subsequent report, in 2006, by Merola and Dunayer, of the Animal Poison Control Center of the American Society for the Prevention of Cruelty to Animals, identified permethrin and canine PSO products as being the single most common cause of feline toxicosis. ³

Far from hitherto being isolated to the USA, feline poisoning with canine PSO products appears to be a worldwide phenomenon, with cases reported from many countries including Belgium, ⁴ France, ⁴ Italy, ⁴ Spain, ⁴ Germany, ⁵ Switzerland, ⁶ Sweden, ⁷ the UK ⁸ and Australia. ⁹ Indeed a detailed description of a further 42 cases of feline permethrin toxicity, treated at a referral hospital in Sydney, is to appear in the next (February) issue of JFMS, coauthored by Boland and Angles. ¹⁰

As is pointed out by Malik et al, cats are recognised to be especially sensitive to permethrin intoxication for reasons that are not fully understood, but may, at least in part, relate to their relative deficiency in glucuronidyltransferase. Not only is permethrin reported to be the most common cause of poisoning of cats in the USA, ² data previously published in JFMS, by Sutton and colleagues, ⁸ showed that permethrin was the most common toxicological cause of feline death reported to the Veterinary Poisons Information Service in the UK, with death occurring in approximately 10–15% of cats exposed to a PSO.

The present paper by Malik et al extends the observations of previous studies by demonstrating that in Australia, too, PSO-associated feline intoxication is a common problem. A total of 750 cases were identified over a 2-year period, with 166 (22%) being fatal. The authors suggest that this probably represents a significant underestimation of the true numbers, and similar observations have been made in previous studies. As the problem is known and recognised by many veterinary surgeons, there is a significant (though unfortunate) risk that these poisoning cases will not always be reported to the manufacturers and licensing authorities. Irrespective, collectively these data are shocking, not just because of the high numbers of cats affected and the high mortality rates, but because this problem is and should be avoidable. Cats suffer intoxication both as a result of the inappropriate use of canine PSO products on the cats themselves, and through secondary poisoning by sharing the environment with a dog that has been treated. The question that has to be asked is why, when so much information is available about feline PSO poisoning, are such cases still so common?

Back in June 2000, the American Veterinary Medical Association Executive Board suggested that product labelling should include clear warnings about the potential toxic and fatal nature of permethrin exposure to cats, including the dangers of secondary poisoning. ¹¹ Sutton et al ⁸ noted that poisonings were continuing despite warnings on the product labels and suggested therefore that current product label warnings were inadequate and/or not visible enough. As reported here by Malik et al, it is likely that most cases of feline PSO poisoning arise from products purchased at outlets other than veterinary clinics (supermarkets, pet stores, etc), where advice to the pet owner from a suitably qualified person is not going to be forthcoming. It is crucial that we heed the call to engage with drug manufacturers, government authorities, distributers and sellers of these products to stop the unnecessary suffering and loss of life that is occurring. Clearly current warnings on these products are inadequate and need to be improved. Further, we support wholeheartedly the call for the licensing authorities to take note of this problem and restrict the sale of PSO products to veterinary outlets, where appropriate advice can be given. Indeed we know from surveying veterinary surgeons in the UK that there is widespread support for such a measure here, as well as in Australia. Bottom line is we need action now to stop these poisonings and deaths.

This 1.5-year-old male neutered ragdoll presented 5 h after dermal application of a PSO with generalised seizures and fine muscle tremors (see video clip at doi.10.1016/j.jfms.2009. 12.002). After 3 days of intensive treatment (diazepam to control the seizures, and sedation for 48 h with a combination of midazolam and propofol constant rate infusions) extubation was possible. The cat was discharged on day 5 with no complications. Courtesy of John Angles

Until such time that better labelling exists and, preferably, the sale of these products is more tightly controlled, cases of feline PSO poisoning will undoubtedly continue. Although a description of treatment of affected cats was outwith the scope of this present study, the anecdotal reports of good responses to low-cost protocols developed by emergency centres are encouraging. An excellent and in-depth review of treatment options and recommendations for managing permethrin toxicity cases is a key element of the article by Boland and Angles to be published next month, and this, too, will be essential reading for veterinary surgeons everywhere.

The Story behind the Study

The ‘how and why’ of this study by Richard Malik and colleagues is an inspirational story of a disparate group of vets (experienced clinicians, new graduates, academics, practitioners, and colleagues in industry) working as a team to tackle an issue that had arisen in practice.

The story began when two of the authors, Anne Fawcett and Erin Bell, encountered cases of feline PSO toxicity. In Anne's words: ‘I saw a permethrin case as a new graduate. I had not been told about this toxicity at university and the textbooks gave a favourable prognosis so I was not aware of the gravity of the situation. I gave a favourable prognosis and the cat died quite an awful death. When I did some research I realised I should have acted more aggressively and sooner. When I spoke to colleagues they had all seen cases that ended in death -yet the stats suggested otherwise. The patient was Cuddles W and I won't forget him, or his owners (two teenage boys who applied a PSO to save money).’

Anne and Erin, both so sad to have lost cats, wrote to the supermarkets and drug manufacturers before ‘venting’ to Richard Malik. This prompted Richard to write an emotive (but ultimately not very successful) letter to the Australian Veterinary Journal. At this point, Stephen Page, a card-carrying pharmacologist, became involved, advising Richard on what exactly needed to be done to influence the regulators.

The team set about conducting a survey to collect the required data. Their efforts were bolstered by Aine Seavers, an Irish vet (with a lot of energy!) who has settled in Australia and conducts research in practice.

As the study neared completion, Professor Michael Ward gave invaluable help with some of the epidemiology and statistical analysis. Merran Govendir provided additional expertise in pharmacology and therapeutics.

We support wholeheartedly the call for the licensing authorities to restrict the sale of PSO products to veterinary outlets, where appropriate advice can be given.