There is a common perception that what is good for us is ok for our pets, and what is safe for dogs is probably safe for cats too. Unfortunately, this is not the case. There are many plants and toxins which are safe for dogs but lethal for cats, just as some medications that are safe for humans can be quite toxic for pets and vice versa. Different species have different physiologies, which can make the veterinary study just that little bit more complicated.
One such medication I wish to discuss today is the flea spot-on products. There are various flea products on the market and none of them should be used interchangeably for cats and dogs. Sure a few products may have the same active ingredients, just different doses for the different species, but there is often a good reason for this. Of specific concern is the pyrethroid family, found in products such as “Advantix” (TM) and ALL of the spot-on flea control products for dogs found at the local supermarket. Pyrethroid products should never be used on cats and should have a warning symbol on them, as shown below.
Problems occur when cat owners fail to notice this symbol and think it might be a cheaper option. I have had clients who thought a medium sized dog dose would be enough to treat both of their cats for fleas. Cats may also develop signs of toxicity if they have been associating closely with a dog who has recently had the spot-on applied, especially if they like to groom their canine companion! Grooming themselves tends to make the poisoning worse as well.
Pyrethroids, like pyrethrin and permethrin, are neurotoxins. They kill insects by attacking their central nervous system. They will also work on the central nervous system of dogs, cats and humans, but to a lesser degree than insects. Insects are far more sensitive to the product partly due to having a smaller body mass compared to the mammals to whom the toxin is applied. The action of pyrethroids is more pronounced at lower body temperatures as well, making insects more susceptible. And cold, sick cats will also be more susceptible to their toxic effects. Toxic effects may also be seen on small dogs treated with inappropriately large doses of pyrethroids.
Absorption through the skin and oral cavity (after grooming) is excellent for these chemicals given how fat soluble they are. The chemical is then metabolised in the liver via pathways that are particularly inefficient in cats, hence, their greater susceptibility to poisoning. It cycles through the blood, liver and intestine which can prolong its effects in the body. Neural tissue is quite fatty and so most of the toxin is drawn to the brain and spinal cord, as well as other fat deposits, and tremors and seizures result.
Signs of pyrethroid poisoning may be seen within minutes to hours after application and potentially up to 3 days afterwards. We commonly see cats in our emergency room who had the toxin applied the previous day. The milder effects include drooling, mild body tremors, possible changes to demeanour (excitable or depressed), and possibly some gastrointestinal signs following ingestion by grooming. More advanced poisoning can lead to ear twitching, local irritation (oral or skin), disorientation, elevation of body temperature, generalised tremors, seizures and death.
There are no specific diagnostics tests that can be performed at the clinic to diagnose pyrethroid exposure so diagnosis is generally made on the basis of clinical signs and history of exposure. Blood tests can be performed to assess general body function which may influence the type of treatment provided if other issues are found such as kidney or liver disease.
Treatment is essential! At the very least, a good bathing and decontamination of the skin and gastrointestinal tract is necessary to prevent the signs from progressing further. On its own this may not be enough though. I have met cat owners who realised the error of their approach very quickly (i.e. within minutes of the application), and bathed their cat immediately, only to still require veterinary attention the following day when signs developed. Most vets will not necessarily recommend hospitalisation if there are no clinical signs evident, though the option of admitting for observation, repeat bathing and gastrointestinal decontamination should be offered.
Activated charcoal is used to bind toxin in the gut in cats that are alert enough to eat and swallow. Charcoal may be given repeatedly during the course of treatment to help bind the toxin as it cycles around the liver and gastrointestinal tract. Intravenous fluids are often administered to support hydration. Some cats may already be dehydrated if they have been tremoring for some time, especially those that have been missing for a day or two. IV fluids are also used for diuresis (pushing urine production), to help the kidneys eliminate toxins from the blood stream. Having a drip line in place also helps to provide intravenous access for medications that may be required urgently to help stop seizures if they occur.
One of the most important parts of the therapy is to help settle the tremors, and muscle relaxants are used for this purpose. Some vets will only have access to diazepam (valium). Methocarbamol is a muscle relaxant we use and more vets are starting to access. Using this drug avoids the unwanted side effects of diazepam (it can make cats very spaced out and difficult to handle in some cases).
More recently trials have been performed using an intravenous infusion of lipid, which is essentially IV fat. Lipid solutions are often used to provide intravenous nutrition for critical patients (partial or total parenteral nutrition). Research has found that providing IV lipid solution to patients who have overdosed on fat-soluble drugs, such as those absorbed through the skin, can help to resolve the clinical signs early and reduce the length of hospitalisation. The use of IV lipids in cats with pyrethroid toxicities has shown promise, though its use at this time is still “off-label” (i.e. although shown to work well, has not been qualified through veterinary medicine licensing boards). Vets are able to use this medicine for pyrethroid intoxications providing both they and the cat’s owner are aware that it is not licensed for this use.
The outcome for cats treated for pyrethroid toxicities is generally excellent, although at quite a bit more cost than the flea product which caused the illness in the first place. It is unfortunate that many of the clients we see with this problem are those who are least able to afford veterinary care. Interestingly, it also seems that cats are more sensitive to this toxin than the fleas, as most of the cats we treat are often still plagued with fleas!