Friday, November 1, 2013

Three things I learned: treatment of toxicities in dogs and cats

Chocolate. Delicious to humans and dogs, but potentially fatal to the latter. (Does make me wonder though...maybe this stuff is just killing me slowly?).
In recent months I’ve treated animals for toxicities and potential toxicities (i.e. decontamination) secondary to ingestion or exposure to zinc sunscreen (the dog ate it), lead, a gigantic and formerly delicious dark chocolate-and-raspberry brownie, batteries, permethrin, ivermectin, anticoagulant rodenticides, xylitol, NSAIDs (most recently ibuprofen), contaminated excrement (yep) and human anti-depressants.

When it comes to potential toxins it pays to be paranoid. Better to induce vomiting if you're unsure that the dog or cat ate your pills than wait until (potentially irreversible) clinical signs develop.

Toxicities are common in companion animal practice and are a major threat to pet health. According to Emergency and Critical Care specialist Dr Trudy McAlees, who gave an excellent webinar via the Centre for Veterinary Education, the main determinant of the outcome in small animal toxicities (apart from the dose the animal was exposed to and the interval between exposure and treatment) is the supportive care. And that rings true. I have been working on a toxicology project and the majority of cases require similar treatment – with a little tweaking.

Effexor aka venlafaxine hydrochloride: exttemely tasty yet toxic to pets.
Decontamination may be achieved by inducing emesis/activated charcoal or gastric lavage +/- a cathartic, or dermal decontamination. The benefit of inducing emesis varies with the toxic agent and the clinical signs of the animal, and may be contraindicated (e.g. in a seizuring or obtunded patient).

[As an aside, a pearl of wisdom for new graduates: you will want to monitor your patients CLOSELY when you induce vomiting. If the patient found it tasty the first time, there is a good chance they will attempt to ingest it a second time. Better to catch the expelled material in a vessel like a cat litter tray and whisk it out of reach].

As so many toxins induce seizures (e.g. metaldehyde, chocolate, pyrethroids), seizure control is essential. Dr McAlees uses 0.5mg/kg diazepam or midazolam IV in the first instance, although she also mentioned that the intranasal route is a reliable route for absorption. If administered per rectum the dose should be doubled to account for the first pass effect.

If this does not work she uses phenobarbitone (10-20mg/kg as a loading dose (takes 10-20 minutes to reach peak effect)) then anaesthesia with alfaxalone CD/propofol or thiopentone (the latter two possibly reducing the metabolic requirements of the brain).

Seizuring animals are at great risk of developing hyperthermia which may exacerbate cerebral oedema. If the core body temperature is 40 degrees Celsius or above, heat sock is a risk. Active cooling via tepid water and a fan is most effective. Dr McAlees stops active cooling when the body temperature reaches 39.5 degrees Celsius. Interestingly, she mentioned that ice packs can cause local vasoconstriction and may not lead to core cooling.

Besides a thorough history, Dr McAlees recommends a PCV/TPP, venous blood gas, lactate, electrolytes and APTT as the minimum database for the intoxicated patient – as well as CBC/biochemistry if possible. Animals whose lactate decreases by 50 per cent of more within six hours have a better prognosis. Commercial kits from the pharmacy can be used for drug detection in urine.

Antidotes are few and far between but may include naloxone for opioid toxicity, atipamezole for alpha-2 overdose and flumazenil for diazepam overdose, in addition to tick antiserum and snake anti-venom.

This greyhoud ate so much ivermectin (left on a bench) that she was comatose for almost a week. She has since made a full recovery. 
The main toxins she focused on were metaldehyde, chocolate and pyrethrins. Her treatment of choice for pyrethrin intoxication is methecarbamol, but she also commented that intravenous lipids may be useful in drawing toxins out of the system (it is also useful in the treatment of ivermectin/moxidectin toxicity, baclofen ingestion, Ca+ channel blocker overdose and THC toxicity – but is off-label). She added that cats which ingest pyrethroids from their fur may also experience an allergic reaction to the carriers and may require dexamethasone.

What toxicities do you see in practice?