Tuesday, 21 February 2012

Toxic Shock - 3 pet poisons to be aware of

There's a little bit of background to this blog before we get to the actual poisons, so if you're in impatient type, or are desperate for the loo and don't want to risk carrying your laptop/smartphone/desktop along with you (and I really wouldn't advise trying the latter) then you can scroll down quickly to have a peek at them to save time.

I had already decided to write a post about common pet poisons before this weekend, mainly motivated by a site that a friend of mine shared on Facebook, discussing the most common toxic materials that pets ingested. Reading through the article, it seemed to bear very little resemblance to my experience of dealing with poisoned animals.

The number one for pet poisons on the list was, as I remember, onions. Now, to be fair, this was a US-centric site, and it's just possible that animal companions in the States have a far more rapacious appetite for eye-wateringly bitter bulbs than those on this side of the Atlantic (or, and maybe just as likely I suppose, it's also possible that I have misdiagnosed a vast number of cases of onion toxicity in my career), but it struck that that almost none of the poisons mentioned were ones that I had seen cause a clinical problem in practice. Rather rudely, I hijacked my friend's thread to point out the substances which I saw regularly in practice. Afterwards, I decided probably the best thing to have done was just to blog about it myself.

I also wanted to blog about something that might actually prove useful to people - I know this in itself is stepping far beyond the normal boundaries of my blog, but what the hell, sometimes I just like to give something back :). A less altruistic reason is that blogs with a 'Top 3' in the title tend be more widely read than those with a crappy pun for a title - I know it's depressing, but don't tell me you haven't occasionally been lured by the promise of the 'Top 5 Celebrity Hair-Related Injuries' or similar - so I decided to have a go at one myself for a change.

My plan was to start relatively light-hearted, and not make it too heavy. Poisoning is a strange one - it seems far easier for people to believe that their evil neighbour has poisoned their companion than something has gone wrong with their metabolism, and their immune system. I often get clients leaning over and whispering to me conspiratorially, 'Well, the man over the road has never liked him. Do you think he might have given him something?'. Ninety nine times out of a hundred, of course, the answer is no. Despite all the things I have seen, and despite the fact that I always think of myself as something of a cynic, I often find it hard to genuinely believe that there are many people out there prepared to maliciously cause harm to animals. That doesn't mean it doesn't happen, it's just that I find it hard to believe. Hopefully, I always will! I might well write something at some point on humanity's schizophrenic relationship with other members of the animal Kingdom.

Anyway, I'm sorry to say the light-hearted approach has somewhat gone for a Burton, because that was before I went to work on Saturday. This weekend I put four cats to sleep because they had been poisoned with antifreeze, all of whom lived in the same street. It's possible (maybe even likely) that this was a deliberate case of poisoning. I mention this not because I want talk about it especially (because it really was very depressing. Incidentally, if you're the type of person who might think 'Well, they're only cats - we poison plenty of rats to death, don't we?' - firstly, I do have some sympathy with that view. Humanity is very good at setting up strange double standards for animals. I may have mentioned in another blog treating a cat that was on a rabbit & chicken diet only, to then have as my next two consultations- you guessed it - a rabbit and a chicken. Secondly, whatever your position on how much animals can suffer (and trust me, they can suffer, terribly) please bear in mind there was quite a lot of human suffering and misery that accompanied these four deaths, too) but to drive home the point that we genuinely do see cases of these poisonings. They're still comparitively uncommon, but they can, and sadly do, happen.

So, that's the background. Below we're going to talk about the three poisons that I and my colleagues see most frequently in practice, with a few honourable mentions. The eagle-eyed amongst you will probably spot this is a fairly cat-heavy blog. At first glance this is unusual, because cats are generally a little more discriminating about what passes their lips compared to their canine brethren. There's a couple of reasons felines are over-represented on the poisoning front, though. Firstly, they are (usually) physically smaller than dogs, and so generally need a much smaller dose of whatever the substance is to cause harm. Secondly, cat's livers aren't really as robust - perhaps versatile may be a better word - as dogs, or ours, and they tend to struggle with a number of substances that we can manage quite readily. It's probably a function of the fact that they're obligate carnivores (they have  to eat meat) as opposed to us, and so their diet tends to be a little less varied.

1 - Ethylene Glycol - Antifreeze

Perhaps unsurprisingly, antifreeze is on my mind at the moment. I mentioned earlier that I wondered if I was naive about people - but perhaps not, because there's a part of me that worries even mentioning how toxic this substance can be to cats might encourage more poisoning. Still, everything is available on the 'net, nowadays, so hopefully this will help more cats than it harms.

The Stuff

Ethylene glycol is a nasty substance - it is toxic to us, and to dogs, but sadly it is especially poisonous to cats - mainly because of their smaller size than anything else.

Ethylene glycol is similar to alcohol, and in the early stages of poisoning, animals (and people) do appear to be drunk. This is rarely the difficult stage, though - the trouble comes when the body metabolises the ethylene glycol to other products. It reacts with calcium on the bloodstream to form calicum oxalate, and it is this that causes the harm, usually in the kidneys. There's an article here that describes the process far better than I can, and has lots more information antifreeze too.

How poisonous is it?

Short answer - very. For cats, the amount they need to take in is tiny - simply licking the outside of a cracked antifreeze bottle would almost certainly be enough to cause irreparable kidney damage. For your average 20kg dog, the lethal dose could be as little as a teaspoonful.

I was always taught that it's doubly dangerous because of it's sweet taste, and that cats would drink it voluntarily quite happily. I'm not at all convinced of that. In my experience, cats aren't especially excited by sugary treats, and antifreeze itself does not take good in my opinion (mind you, I think that about badger faeces too and both my dogs disagree) but it's poisonous enough that simply cleaning it off their fur is likely to give them a fatal dose.

Is there an antidote?

The other thing about poisons - people tend to assume there's an antidote, just like the exciting-looking vial of blue fluid that Indy spends the first act of Temple of Doom trying to grab. Sadly, in real life, it doesn't usually work that way, and the vast majority of poisons have not antidote at all, and you just have to deal with the symptoms.

That said, antifreeze poisoning dose have an antidote of sorts. As I say, the dangerous stuff is really the calcium oxalate that comes from metabolising the stuff. The enzyme in charge of the transformation is alcohol dehydrogenase, the same guy who's mops up all the wine you've got in your system after a crappy day at work. Give him enough alcohol to deal with, and he's so busy with it that most of the antifreeze gets peed out of your system without changing, and you're safe.

Great, in theory. The problem is the speed of ethylene-glycol related kidney damage. If you don't get the alcohol in within twelve hours of ingestion, you're probably too late. All you're likely to have seen by then, if you didn't see them actually drink the stuff, is a bit of wobbliness. The problem, for a clinical perspective, is that an awful lot of conditions cause a bit of wobbliness, and if we admitted them all and gave them intravenous vodka, we'd probably kill more cats than we saved.

The take-home message, then, is that if you know or suspect that your pet has taken in antifreeze, get them to the vets as soon as possible, and let the vet know that's what you're worried about.


Pretty bloody awful, I'm sorry to say. The vast majority of cats (and it's usually cats) that present to us with antifreeze poisoning are already in kidney failure, and by then it's too late. Almost all of them end up getting euthanased.

So, if you have antifreeze at home, bear all of this in mind - clean up any spillages on the bottle, or on the drive, and keep pets away!

2 - Lillies

Another one for cats, I'm sorry to say - in fact, in a way this is even worse, because it is quite a common poisoning for kittens. They need an even smaller dose than adult cats, and they tend to be a bit more inquisitive.

The Stuff

Good question! As far as I'm aware, no-one is entirely sure of the mechanism of action for lily poisoning, but there are a number of points about it.

Firstly, it seems to be specific to cats - other animals may vomit or get diarrhoea if they scoff one, but for cats, lily poisoning leads to old enemy, kidney failure.

The second point it - whatever the toxin is, it is in every part of the lily. Secondly, the lethal dose, as with antifreeze, is miniscule. I've known cats that brushed against a lily plant and licked the pollen off their fur to end up with severe kidney damage.

Not every species of lilly is as poisonous as the others - there's a list of the toxic species here - but unless you're a horticulture expert, the best thing to do is just avoid them altogether when cats are involved.

How poisonous is it?

As mentioned above - very. Nibbling a leaf, petal or stamen can all be quite enough to destroy the kidneys.

Is there an antidote?

As no one is sure what the toxic substance is, no one can counter it. The only thing that can be done with lilly poisoning, as with a lot of poisoning, is damage limitation - try and prevent the bloody stuff getting absorbed. To the vet, this means putting the cat on a drip (to 'flush the system through' and support urine flow), making them vomit (if they ate the stuff within 30 mins - 1 hour) and preventing absorption from the stomach by feeding things like charcoal paste.


Pretty crappy, I'm afraid. Just as with antifreeze, by the time you work out what's going on, it's often too late. I've had some extremely sad cases where lilies have been around the house due to the funeral of a family member, and as a consequence a few days later the family cat is brought in to us.

The vast majority of these cases get put to sleep too, I'm sorry to say. Take home message - either keep lilies well away from cats, or (my advice) just don't have lilies in a house where you have cats. It's too risky.

As with antifreeze, if you know or suspect your cat has been in contact with a lily, get it to your vets as soon as possible to try and limit absorption.

3. Rat-bait poisoning - Warfarin and the Coumarins

One of the classics - in that everyone seems to know a little about rat poison, and it's also probably the most suspected poison by clients of the three on this list - but that doesn't mean it never happens. Sadly, it does, relatively frequently. It's also one of those strange 'double-standard' poisons - it's dreadful if pets take it in, but it's fine to kill rats with it. I won't ponder the mysteries of the human mind any further though - I can't pretend I'm not a hypocrite either. I suppose we've all got to draw the line somewhere. Shall we press on?

Rat poison is the first on the list to affect more dogs than cats - largely because most cats have more sense than to tuck into a load of weird-smelling blue pellets.

The Stuff

Warfarin and the Coumarins may sound like a Glam Rock band, but they are actually the active ingredients of rat poison. You're probably already familiar with warfarin. It's mechanism of action is to inhibit an enzyme by the long-winded name of vitamin K epoxide reductase - and it's this enzyme that has the job of recycling used vitamin K in the system. Without it working, you run out of vitamin K very quickly.

Vitamin K is a vital component in the 'coagulation cascade' - a group of proteins which, along with protein, allow your blood to clot and prevent it from all leaking out of you when you are lightly burst. Without vitamin K, a number of these proteins fail to form, and without them you're at risk of bleeding to death.

Warfarin (I'm sure you're aware of this but I'm telling you anyway) is used at low doses in human medicine to 'thin the blood' - what it actually does is reduce your risk of getting a clot within your bloodstream (a thrombus). What you might be less aware of is that it isn't used in rat poison any more, because almost all rats are greatly resistant to now, on account of humanity feeding them lots of it down through the years.

The coumarins (of which warfarin is a so-called '1st generation' one - nothing to do with Captain Kirk) are used instead nowadays - usually 3rd generation ones such as brodaficoum or difenacoum) all work in a similar way to warfarin, the main difference being that the more modern drugs work for much longer, and are far more potent.

The symptoms of this kind of poisoning are the sort of thing you would expect - blood, from anywhere. If a dog is bleeding in two unrelated sites (for instance in the pee and from the mouth) or if there are tell tale signs of bleeding in the gums or the eyes (petechial haemorrage) then rat poison is on our list of diagnoses. Lethargy is another common sign due to the anaemia, as well as blue-coloured vomit or faeces (simply from the blue dye in the pellets - just like slug bait poisoning)

How poisonous is it?

The answer to this very much depends of exactly which coumarin has been eaten, but as most rat poisons are second- or third-generation nowadays I'm going to refer you to my sadly standard answer - very. We can work out the exact doses, but basically if your dog or cat has definitely eaten any amount at all, it could be in trouble.

Is there an antidote?

By now you might well have read how the coumarins work, and you can probably take an educated guess at the antidote if you don't know it already - Vitamin K.

As with all poisons, the best thing you can possibly do it get in early and prevent absorption as soon as possible. If you can't get to it in time, vitamin K will do the job, but it takes 24-48 hours to work, because it needs to get synthesised into the clotting factors, so the dog usually has to stay in the practice on fluids, and occasionally will need a blood or plasma (basically blood minus the red blood cells - easier to store and transport, and gives the dog a whole load more clotting factors to work with) transfusion if the bleeding is too severe.

Coumarin drugs remain in the system for a long time - the dog is likely to have to take vitamin K supplements for 3-4 weeks after the poisoning incident.


Refreshingly, the outcome is often better than the other two toxins we've discussed already. Partially because people are well aware of the poisonous nature of the substance (it is called rat poison, after all), and partially because the antidote can work even a few days after exposure, we generally have a good chance of getting animals dosed with rat poison through. Sadly, we still see some cases too late or too far gone to influence the outcome, but fortunately these are the minority rather than the majority (unlike lily and antifreeze poisoning)

So, there we have it...the three (arguably) most common toxins I see in my daily life as a small animal vet in   south west England. For the argumentative amongst you, there's a few honourable mentions for other toxins below - some serious, some less so. Here we go...

Flea products - Permethrin poisoning in cats. First thing to say - NEVER USE A PERMETHRIN-BASED FLEA PRODUCT ON A CAT. There are still some dog flea 'spot ons' that use permethrin - do not be tempted to try a small dog dose on a cat and think you'll get away with it. Permethrin causes severe seizures and death in cats, and I've known it happen from a kitten licking the wet patch on the back of a dogs neck. If in doubt, never use a supermarket or pet shop flea spot on for a cat, get them from your vet instead.
House flea sprays, including those bough from vets, can contain permethrin too, so keep your cats away from sprayed rooms.

Grapes - I was surprised and embarrassed to discover this one a few years ago, because I knew nothing about it. In fact, I've been known to feed the odd grape to my greyhound (thankfully without consequence other than being badgered to give her another one). The reason I've managed to remain ignorant of it is because a dog needs to eat quite a few grapes to get problems, and some dogs seem very resistant to the problem. It causes severe vomiting and diarrhoea, and in extreme cases can cause kidney failure. Remember than raisins are grapes too, and can cause them same problems.

Slug-bait poisoning - metaldehyde. Can be extremely toxic, usually seen in dogs. It can cause severe seizures and death, though for whatever reason I've never come across it in my career. It may just be luck, but I'm hoping that means it isn't all that common nowadays. If it happens, though, you need to be in touch with you vet quickly.

Chocolate - at my practice we're commonly quizzed about this, what with dogs being dogs and chocolate being chocolate. The toxic substance is theobromine - which is actually technically poisonous to us as well, although we'd have to consume a good few kilos of chocolate before it started to have any effect, and by then you may have other more pressing social problems such as being shunned/arrested for eating your way through an entire sweet shop.
Dogs are a little more sensitive to theobromine than we are, but even then the dose required is comparitively large. The other saving grace is that the cheaper and milkier the chocolate, the less theobromine it has in it, so the problems tend to come with small dogs (less body weight) and expensive dark chocolate (more theobromine). Our own greyhound ate her way through an entire tray of Guylian belgain choccies, and although I can't quite say she didn't suffer any ill effects (because my wife was not at all impressed with the theft), she certainly didn't get theobromine toxicity.
If you're in doubt, ring your vet with the chocolate wrapper to hand and, ideally, your dogs weight -we can usually work out how much would be too much from there. And I'm sure you understand why I've mainly talked about dogs, here, but theobromine can also be toxic to cats.
Symptoms are usually vomiting and diarrhoea but can progress to seizures and serious problems with higher doses.

Paracetamol - dogs will tolerate this, and we do occasionally use it in them, although the cut off between 'safe' and 'toxic' doses in dogs is a little narrow for comfort. Cats, however, lack the required liver enzyme to deal with it, and a SINGLE HUMAN DOSE OF PARACETAMOL CAN KILL A CAT. Never be tempted to use human painkillers in cats - not even child doses like Calpol (UK).

Human medications - although animals can often be buggers to take their own tablets, they often find their owner's medications irresistable. Toxicity and problems of these vary wildly, so it's best to ring your vet if you find your dog happily sitting on top of a tablet box with a few scraps of silver foil hanging out of their mouths - but to reassure you, as a general rule anti-depressants and contraceptive drugs are usually pretty safe.

Minoxidil (Regaine or Rogaine) - For gentleman, like me, whose brain is so hot with energy and imagination that their hair starting to fall out due to the intensity of the supercomputer that nestles beneath it, it's worth being aware of this particular product - for those of you who (damn you!) don't know anything about this product( because you've never had to worry about that perfect head of hair you flaunt horribly to us baldies (or in my case, soon to be baldie) Regaine is a sticky ointment that you rub on your bald patches and hope that something starts to happen up there.
Well, you also need to know that it's highly toxic to cats - It's another one for the liver hall of fame, I'm afraid. They (and you can probably say this along with me by now) lack the required enzyme to metabolise it, leading to dangerously low blood pressure, pulmonary oedema and death. It's just about treatable, if caught in the early stages. Thankfully I've never seen this particular poisioning, but I nearly caused it myself in my own cat. Ignoring the old adage that 'you can't polish a turd', I sadly bowed to vanity and got myself some of this stuff - only realising after some internet research quite how poisonous it can be for cats. Now, I wasn't planning to rub it onto my pussy (quiet at the back! Although, sadly, I do believe some people have tried this; don't) but you are supposed to rub it onto thinning patches before you go to bed. Our cat likes to sleep on our pillows. You can probably see where this is going - suffice it to say the drug is potentially toxic enough that if your cat licks your pillow it could end up in serious trouble. I've decided not to use it at all, and to age with whatever dignity I can muster. Just be careful with the stuff.

Okay, well, I think that's enough to be getting on with. I hope that was of some help, and not to depressing!

See you all soonish.


  1. Just found your blog because you started following mine - I found this post really interesting as we have two cats who chew on absolutely everything they can, so it's useful to know what we should keep out of the house. Cheers!

  2. Glad it's been helpful, Paul. Very keen on your blog by the way - I have a huge stack of gamebooks too. Interested to see what you think of my favourites! I did a similar thing to you, last year, after meeting Steve Jackson and Ian Livingstone at UK Games Expo, but didn't think to write a blog about it. Looking forward to future installments :)