Permethrin Poisoning in Cats: an Under-Reported Global Issue

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Permethrin poisoning in cats: an under-reported global issue

Author : Robin Fearon

Categories : RVNs

Date : January 1, 2012

Robin Fearon highlights how owners’ misuse of a canine spot-on flea product is having fatal consequences in cats

ACCIDENTAL flea treatment poisonings are a real and present danger for cats. The problem is a felinetoxic parasiticide in canine flea treatments called permethrin. Many owners administer it unknowingly or accidentally and the results can be fatal. So how practices inform the debate about permethrin is crucial to reducing poisoning incidents.

Speaking at the International Society of Feline Medicine (ISFM) meeting at September’s Southern European Veterinary Conference, Lara Boland outlined the importance of both clear drug packaging and access to veterinary advice in helping owners to understand the risks. Lara is the Feline Advisory Bureau (FAB) scholar at Langford Veterinary Services small animal hospital and understands clearly the dangers of permethrin.

“Even small quantities of permethrin can cause severe and fatal poisoning,” she explained. “There are reports of even one drop of concentrated spot-on causing clinical signs, of cats being poisoned by licking empty spot-on packets. The signs include general muscle tremors, twitching, seizures, hyperaesthesia, ataxia, pyrexia and metriosis.”

Many canine flea spot-on products contain permethrin because dogs are less sensitive to its effects. Supermarkets and pet shops stock them because they are popular among pet owners and cheap. “We know these products are bought from supermarkets without owners seeking veterinary advice or supervision,” said Lara.

1 / 6 “Often, they don’t know that they can only be used on dogs. Sometimes owners buy products for both cats and dogs, then mix them up when they get home. Owners may even see warning signs on the packaging and still not understand that they can cause fatal poisoning when used on cats.”

Permethrin flea treatments are liquids applied to the skin on the back of the neck and absorbed for systemic effect. Permethrin itself is a pyrethroid insecticide – a synthetic analogue of pyrethrin – derived naturally from chrysanthemum flowers. It is a neurotoxin that binds to and blocks sodium channels on the surface of cells, interfering with nerve function and causing cells to repeatedly discharge. Even when restricted solely to canine use, cats living in the same household as dogs treated using permethrin can become affected through touching or grooming. It is a thorny problem.

“We know that cats are highly sensitive to permethrin and they are more likely to develop signs of toxicity than other species,” said Lara. “Permethrin is metabolised by the liver and cats may develop a reaction because of different hepatic metabolic pathways to other species. This is what causes clinical signs.”

Signs of toxicity usually develop in a few hours, but can take between 24 and 48 hours to evolve. If a cat is severely affected then treatment may be extremely intensive and expensive. There is no antidote and treatment involves three factors: decontamination by washing – and sometimes fur clipping – to remove as much permethrin as possible and prevent further absorption; seizure and tremor control; and supportive care, such as intravenous (IV) fluids and warming (if needed).

Drug therapy reduces tremors and seizures but varies according to pharmaceutical availability, drug preference and how badly affected the patient is. Methacarbamol is a central muscle relaxant that can be given half IV and the rest to effect (200-300mg/kg per day). Other medications include benzodiazepines, such as diazepam and midazolam, or barbiturates like phenobarbitone.

“Severely affected cats may require general anaesthesia through propofol continuous rate infusion,” Lara said. “Some require prolonged hospitalisation and may develop complications during treatment. Cats with really severe signs may not survive, especially if they present to the clinic late in the course of toxicity.”

Lara would ideally like to see a ban on all permethrin products but admits it would be tough to achieve as the products have been around for a long time. “The real problem is misuse by pet owners and not the products themselves,” she admitted. “Clearer labelling and prominent warnings may prevent clients from accidentally using these products on cats. Separating cat and dog products on the shelf in supermarkets and pet shops may help to reduce the incidence of clients mixing up the products. Alternatively, restricting their sale to practices may be another option.”

Just how widespread is permethrin toxicity? Lara said that despite knowledge of its poisonous effects in cats, it has probably been under-reported. “It is only recently we realised what a big

2 / 6 problem it is,” she said. “Permethrin products are used in many countries and there are large numbers of case reports from the UK, US and Australia. We know it is a global issue and the most common cause of cat poisonings in the US. It has been reported as the most common toxicological cause of death in cats reported to the VPIS and estimates detail hundreds of cat poisonings each year.”

A French report detailed a total of 465 animal poisonings, 14 per cent of which were identified as pyrethroid toxicity. A report from Italy stated that 67 per cent of cat poisonings were caused by pyrethroids. The UK’s VPIS recorded 286 cases. British and Australian studies say mortality rates arising from contact with permethrin are between 11 and 37 per cent – died or were euthanised.

Lara described a case brought into an animal referral hospital in Sydney, Australia. Max was a two- year-old neutered Burmese cat whose owner had applied a supermarket brand flea spot-on made for large dogs. Max was admitted to the hospital seven hours later after he started showing distressing clinical signs.

“He had quite severe generalised muscle tremors and was hyperaesthetic,” she said. “To treat Max we placed him in a dark quiet room and started IV fluids. We gave him diazepam intravenously but this only had a temporary effect. In the end he required heavy sedation and anaesthesia – a propofol continuous infusion (used for 26 hours in this case) – in combination with midazolam continous-rate infusion for about 40 hours.”

Clinicians washed Max with a mild detergent to remove as much permethrin from the skin as possible and he was so severely sedated that it was necessary to intubate him. He was given oxygen and a urinary catheter was placed so fluid outputs could be monitored and fluid intake rates adjusted as required. Heating mats were used to retain normal temperature and ocular lubrication applied. End-tidal carbon dioxide levels, blood pressure and urine output were monitored continuously.

There were complications on the third day after he was extubated and radiographs revealed mild aspirational pneumonia, which cleared up with broad-spectrum antibiotics by day 12. Max also developed a superficial corneal ulcer despite ocular lubrication. This was also treated and resolved.

“The outcome was good,” said Lara. “He survived, although his tremors lasted a total of 44 hours before they resolved. He was walking by the third day and eating on his own by the fourth. He was in hospital for five days in total. On follow-up he was back to normal, but his owners had quite a large bill at the end.”

Effectively, pet owners require education, and the veterinary team needs to be more aware of the issues to bring permethrin poisoning under control, said Lara. To that end, the ISFM is spearheading initiatives for owners, veterinary workers and professional associations, as well as manufacturers and regulatory authorities.

3 / 6 Precedents exist for this integrated approach. “In Australia there has been quite an organised approach to the problem,” said Lara. “A focus group was formed involving the Australian Veterinary Association, various product manufacturers and the Australian Pesticides and Veterinary Medicines Authority [APVMA]. The APVMA did some research to investigate owner attitudes to permethrin products and their use, as well as some research into different types of warning labels.

“They found very poor owner awareness of this problem. They found that having larger, coloured warnings – red and green labels – and correctly positioned warnings, on the front and back of the pack, was important. Having text and pictures – a picture of a cat with a cross and a picture of a dog with a tick – as well as text saying ‘toxic to cats’ or ‘fatal to cats’ was also important.”

A consumer awareness campaign will begin in Australia next year. In the US, similar activities are being coordinated through the Environmental Protection Agency. On top of that, a review of labelling and improvements on existing labels is being pushed through for these products, as well as review, testing and evaluation procedures for permethrin flea products.

At a local level there is much more the veterinary team can do to raise awareness. “Spreading the word is important,” Lara concluded. “Let colleagues and clients know about this issue. We should encourage clients to use products correctly and read the labels carefully – to follow the instructions on labels. It is also important to report adverse reactions in cats, whether that be medication or inadvertent use of drugs for other species, so that we have a clear idea of the rate of these types of incidents in cats.”

Veterinary professionals should take a “belt and braces” approach and report adverse reactions to both the VPIS and the VMD. “The VMD would very much like to know about this,” said Claire Bessant, the FAB’s chief executive. “They have far fewer reports than the VPIS in the UK and, as a consequence, they did not think it was a big problem. When we conducted a practice survey we found that each clinic probably saw about three cases per year. That is a lot of cats.”

Permethrin is not about to go away. It is a cheap way to treat fleas in dogs and its popularity on supermarket shelves means owners will continue to purchase it en masse.

“We have to see if they are getting advice on these products and how well the danger signs are marked on labelling,” Claire concluded.

“We have been trying to make sure that it is not just on the outside packaging, but on the inside and on the vial of medicine itself.”

Comments from NOAH members actively involved in this area

4 / 6 • NOAH members work with the VMD to ensure that their products contain the necessary warnings on packaging and on the product itself to ensure that users of the product receive adequate warnings.

• The VMD and NOAH members monitor trends in suspected adverse reactions. Based on these trends and reports, changes can be made to product classification and product labelling if the adverse reactions suggest that such changes are needed.

• NOAH and its members believe the current distribution systems ensure the availability of medicines to treat commonly occurring problems like fleas, while at the same time ensuring sufficient safeguards are in place.

• NOAH members believe that it is important that users of animal medicines carefully read the product packaging and closely follow any warnings or instructions that are present.

• Keep cats separated from recently treated dogs. There are reports of toxic effects in cats that groom or contact dogs treated 48 hours earlier.

• Toxic effects include behaviour changes, drooling, tremors and death.

• Seek veterinary advice immediately if you suspect toxicity in a cat.

Logo and labelling development

• New label warnings are to appear on permethrin spoton flea and tick treatment products for dogs in Australia thanks to a campaign by the Australian Veterinary Association (AVA). The new graphic image will appear on the front of packages on its own, while on the back it will be accompanied by the wording that includes the secondary toxicity statement.

• The AVA has been running a campaign to improve the labelling since 2008, when Richard Malik and other AVA members raised their concerns about the number of cases of permethrin toxicosis they were seeing in cats, and initiated a national survey to gauge the number of such cases presenting to veterinarians in Australia.

5 / 6 • The 255 survey responses described 750 individual cases of feline intoxication that had presented for treatment in the previous two years: 166 deaths were reported. While most cases of intoxication were reported to be due to directly treating cats with permethrin spot-on products (primary intoxication), a small number resulted from close contact between cats and recently treated dogs (secondary intoxication).

• All high-concentration permethrin products are approved only for use in dogs and specifically warn against use in cats, but the warnings appear to be ignored or overlooked by some users. Some reported to the veterinarian that they didn’t see the warnings, while others thought the warning was just a sales ploy to get them to purchase a more expensive cat product, so they ignored it.

• With support from the Australian Pesticides and Veterinary Medicines Authority (APVMA) and permethrin spot-on product registrants, the AVA commissioned a market research company to develop and test more effective warning messages for inclusion on all permethrin spot-on products for dogs. The new labels will be supported by educational campaigns to warn owners of the dangers of permethrin to cats and to draw attention to the new labelling scheme.

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