Lara Boland, FAB Resident at the University of Bristol, completed a study in feline permethrin toxicity in her native Australia. She shared her knowledge with delegates at the 2010 FAB conference.

What is permethrin?
Permethrin is a pyrethroid insecticide. Pyrethroids are synthetic analogues of pyrethrins which are naturally occurring substances extracted from Chrysanthemum flowers. Permethrin is a neurotoxin that works by binding to and blocking open sodium channels on the surface of nerve cells. This interferes with nerve function by causing the nerve cells to discharge repetitively.

Cats are highly sensitive to permethrin and are more likely to develop signs of toxicity than dogs. Permethrin is metabolized (broken down by) the liver. It is suspected that cats may be more likely to develop permethrin toxicity because they have different liver metabolic pathways to other species — in particular, they have a deficiency in the enzyme hepatic glucuronosyl transferase.

Pemethrin poisoning video A Ragdoll cat which luckily survived to tell the tale. The cat suffered seizures and tremors after a permethrin spot-on treatment designed for dogs was applied to its skin. After three days of intensive treatment and 48 hours’ sedation the cat was discharged with no complications.

Signs of toxicity
Exposure to even small quantities of permethrin can cause severe and fatal poisoning in cats. Common clinical signs of toxicity include: muscle tremors, twitching, seizures (see the video clip, right), salivation, incoordination, fever and dilated pupils. After exposure to permethrin, signs of toxicity usually develop within a few hours but in some cases can take one to two days to become apparent. Diagnosis is made based on a known exposure to permethrin and clinical signs of poisoning.

How do cats become exposed to permethrin?
Sadly, cats are usually exposed to permethrin when pet owners inadvertently apply permethrin-containing flea spot-on products, which are made for dogs, to cats. These products usually come in a small pipette and the liquid is applied onto the skin on the back of the neck. The liquid is then absorbed through the skin and into the body.

Many different flea spot-on products and flea rinses that are manufactured for use on dogs contain permethrin. Because dogs are less sensitive to the toxic effects of permethrin, these products are safe to use on dogs but not on cats. These products are sold in supermarkets, pet shops and veterinary practices. They are often inexpensive and widely available.

Problems usually occur when pet owners buy these products off the shelf from supermarkets where there is nobody available to explain their safe use. Often owners do not realise that the products can only be used on dogs, accidentally mix up different dog and cat products, or they do not understand that they can result in fatal toxicity if used on cats. Another route of cat exposure can occur if there is a dog in the household that has the product applied and the cat then grooms the product off the dog. It is unknown exactly how long cats should be separated from dogs after dogs have had permethrin products applied.

How big is the problem?
Permethrin spot-on products are used in many countries around the world. There are now several reports of feline permethrin toxicity involving large numbers of cats from several different countries (including the UK, USA and Australia). For example, a recent UK study described 286 reported cases and a recent Australian survey of veterinarians identified 750 cases of feline permethrin poisoning over a two year period. Permethrin has been reported to be the most common cause of poisoning of cats in the USA and the most common toxicological cause of death of cats reported to the UK Veterinary Poisons Information Service.

Based on these published surveys and reports the FAB estimates that hundreds of cats are affected each year in the UK. These published reports are most likely just the tip of the iceberg. It has been suspected for some time that many feline permethrin cases go unreported either because people do not take the time to report them or because they do not know how to report them.

There are also anecdotal reports that the number of feline permethrin toxicity cases may have been increasing over the past several years. There may be many reasons for this including ease of access to permethrin flea products, the low cost of permethrin flea products and the recent economic downturn.

Treatment
Treatment of cats with permethrin poisoning can be intensive and expensive. There is no antidote for permethrin poisoning. In general terms treatment involves decontamination, seizure/tremor control and supportive care.

Because most cats are exposed after having permethrin products applied to their skin, decontamination involves thorough washing of the cat with lukewarm water and a mild hand-dishwashing detergent. The aim is to remove as much of the oily product as possible to stop further absorption through the skin.

Treatment of muscle tremors may involve the use of methocarbamol (a centrally acting muscle relaxant) or benzodiazepines (diazepam or midazolam). Treatment of seizures may involve the use of drugs such as benzodiazepines, barbiturates (phenobarbitone) and sometimes even general anaesthesia or heavy sedation is required (propofol or
alfaxalone).

Supportive care involves an intravenous drip, temperature monitoring and other nursing care. Cats will usually require a few days of treatment in hospital before slowly recovering.
Some cats with severe signs do not survive, require prolonged hospitalisation or develop complications.

Survival rates
Reports from the UK, USA and Australia record between 11% and 37 % mortality rates (died or were euthanased) among cats with permethrin toxicity.

What can be done to prevent toxicity?
There are many things that can be done to reduce the incidence of feline permethrin toxicity. It would be ideal if permethrin-containing flea products were banned because there are many other safer flea control products available to use. Achieving a ban is difficult and may not be possible however.

Many reported cases of feline permethrin toxicity have occurred when owners do not read flea product labels properly or when the labels are not clear. Some dog and cat flea products containing different ingredients have similar sounding names and appearance, also sometimes leading to pet owner confusion. Some products do not have explicit enough labels explaining that cats may die if exposed to the product.

Clearer labelling of these products with prominent warnings explaining that they are toxic if applied to cats and also if cats are in contact with dogs that have had the products applied would help to reduce misuse by owners. Separation of dog and cat flea products on product display shelving may also help to reduce confusion.

Another option would be to restrict the sale of permethrin-containing flea products to veterinary practices or to pet shops where someone is trained in giving advice and help with products, so they can be sold with appropriate advice from trained staff. This would avoid the problem of pet owners buying the products from supermarket shelves without advice.

Education is another key area. Education of pet owners to alert them to the possible dangers of permethrin-containing flea product use on cats and to encourage them to read labeling carefully is an important way to help reduce the incidence of feline permethrin toxicity. Alerting veterinarians to the extent of the problem and encouraging them to discuss this issue with their clients will also help to increase awareness among pet owners.

Another important aspect involves reporting of feline toxicities so that up to date information is available about the extent of such problems. Toxicities or adverse drug reactions in animals, can be reported to the Veterinary Medicines Directorate (www.vmd.gov.uk) and to the product manufacturers by pet owners and veterinarians alike. Additionally adverse reactions can also be reported to the Veterinary Poisons Information Service by veterinarians.

What is FAB doing to help?
FAB has been actively involved in educating pet owners, members of the cat community and veterinarians about feline permethrin toxicity. This has been achieved through conferences and also letters to and publications in magazines and veterinary journals. FAB has been actively involved in discussions with the Veterinary Medicines Directorate to try to make the reporting of adverse events easier and to discuss the potential for restricted sale of permethrin products. FAB has also worked closely with the Veterinary Poisons Information Service to better characterise the extent of the problem and the issues involved in feline
permethrin toxicity in the UK. FAB has also actively contacted permethrin flea product manufacturers to discuss the development of clearer labelling of products to reduce the risk of accidental inappropriate use by pet owners. Additionally FAB has been active in discussing permethrin toxicity with veterinarians and veterinary organisations in other countries to share and help spread information and support about this important issue.

What can you do to help?
Spread the word, let your friends know about this issue. Be sure to read product labels carefully and, if in doubt, ask your local veterinarian for advice. If you are aware of adverse reactions in cats after the use of medications or other products then discuss reporting the event with your local veterinarian.

References
1. Sutton N M, Bates N, Campbell A. Clinical effects and outcome of feline permethrin spot-on poisonings reported to the Veterinary Poisons Information Service (VPIS), London. Journal of
Feline Medicine and Surgery 2007; 9: 335—39.
2. Linnett P J. Permethrin toxicosis in cats. Australian Veterinary Journal 2008; 86: 32—35.
3. Meyer E K. Toxicosis in cats erroneously treated with 45 to 65 % permethrin products. Journal of the American Veterinary Medical Association 1999; 215: 198—203.
4. Malik R, Ward MP, Seavers A and others. Permethrin spot-on intoxication of cats: literature review and survey of veterinary practitioners in Australia. Journal of Feline Medicine and Surgery 2010; 12: 5—14.
5. Boland L A, Angles J M. Feline permethrin toxicity: retrospective study of 42 cases. Journal of Feline Medicine and Surgery 2010; 12: 61—71.