1.4 Small Animal Toxicology & Poisoning Emergencies

1.4 Small Animal Toxicology & Poisoning Emergencies

Toxicoses are among the most common canine and feline emergencies, and the NAVLE tests them heavily because correct management hinges on knowing dose thresholds, the specific antidote, and the decontamination window. A veterinarian who confuses markup with margin loses money; one who confuses toxic doses loses patients. This section organizes the highest-yield small-animal poisons around the clinical decisions an entry-level practitioner must make in the first hour.

The General Approach to the Poisoned Patient

Every toxicology question rewards a structured approach:

1. Stabilize first. Airway, breathing, circulation, and seizure control precede decontamination. A seizing patient is not a candidate for oral decontamination.
2. Decontaminate when appropriate. Induce emesis only in an asymptomatic patient with a recent (generally <1-2 hour) ingestion of a non-caustic, non-petroleum substance and no contraindication (no seizures, no depressed gag reflex). Apomorphine is the emetic of choice in dogs; dexmedetomidine or hydrogen peroxide 3% is used in cats (never ipecac). Follow with activated charcoal (1-4 g/kg) for toxins that undergo enterohepatic recirculation.
3. Give the antidote and supportive care. Most poisons have no specific antidote and are managed with fluids, anti-emetics, and organ support.
4. Contact a poison control center (ASPCA APCC or Pet Poison Helpline) — the exam expects you to recognize these as resources.

Methylxanthines (Chocolate & Caffeine)

Theobromine and caffeine are the toxic methylxanthines in chocolate. Toxicity is dose-dependent and rises with cocoa content: baking chocolate and cocoa powder are far more dangerous than milk chocolate.

• Mild signs (vomiting, diarrhea, polydipsia): ~20 mg/kg methylxanthines
• Cardiotoxicity (tachycardia, arrhythmias): ~40-50 mg/kg
• Seizures: ~60 mg/kg

Management is decontamination, repeated activated charcoal (methylxanthines undergo enterohepatic recirculation), IV fluids, anti-arrhythmics (e.g., lidocaine for ventricular tachycardia), and often a urinary catheter because methylxanthines are reabsorbed from the bladder wall.

Xylitol

Xylitol, a sugar alcohol in sugar-free gum, candy, peanut butter, and some liquid medications, is one of the most dangerous canine ingestions. In dogs it triggers a dose-dependent insulin release and, at higher doses, hepatic necrosis:

• >0.1 g/kg (100 mg/kg): risk of profound hypoglycemia within 30-60 minutes
• >0.5 g/kg (500 mg/kg): risk of acute hepatic failure and coagulopathy (onset 24-72 hours)

Check blood glucose immediately, supplement with IV dextrose, monitor liver enzymes and coagulation, and provide hepatoprotectants (e.g., S-adenosylmethionine, N-acetylcysteine) for hepatotoxic doses. Cats are not considered clinically susceptible.

Ethylene Glycol (Antifreeze)

Ethylene glycol itself is only mildly toxic; its hepatic metabolites (glycolic acid → oxalic acid) cause a severe high-anion-gap metabolic acidosis and calcium oxalate crystalluria with acute kidney injury. Clinical course: early ataxia/"drunkenness" and PU/PD → apparent recovery → oliguric/anuric renal failure.

The antidote blocks alcohol dehydrogenase to stop metabolite formation, so it is only useful early:

• Fomepizole (4-methylpyrazole) is the preferred antidote; ethanol is the alternative.
• The therapeutic window is roughly 8 hours in dogs and only 3 hours in cats — waiting for confirmatory testing is often inappropriate.

Diagnosis is supported by high-anion-gap acidosis, hyperosmolality, and calcium oxalate monohydrate crystals in urine.

Anticoagulant Rodenticides

Second-generation anticoagulant rodenticides (brodifacoum, bromadiolone) inhibit vitamin K epoxide reductase, depleting the vitamin-K-dependent clotting factors (II, VII, IX, X). Because factor VII has the shortest half-life, the prothrombin time (PT) rises first, typically 36-72 hours after ingestion — clinical bleeding is delayed.

• Antidote: vitamin K1 (phytonadione) 2.5-5 mg/kg PO divided q12h, given with a fatty meal to aid absorption.
• Duration: 3-4 weeks for long-acting second-generation products.
• Recheck PT 48 hours after the last dose; if prolonged, extend therapy.
• Actively bleeding patients need fresh frozen plasma or whole blood for immediate clotting factors — vitamin K1 takes 6-12 hours to work.

Acetaminophen (Cats vs. Dogs)

Cats lack sufficient glucuronyl transferase and are exquisitely sensitive to acetaminophen, developing methemoglobinemia (chocolate-brown mucous membranes, facial/paw edema) at doses as low as 10 mg/kg. Dogs are affected at higher doses and tend toward hepatotoxicity. The antidote is N-acetylcysteine (NAC), which replenishes glutathione; ascorbic acid and SAMe are adjuncts.

True Lilies (Cats)

All parts of true lilies (Lilium and Hemerocallis species — Easter, tiger, day, Asiatic) — including pollen and vase water — are nephrotoxic to cats. Even minor exposure can cause acute tubular necrosis. There is no antidote: aggressive IV fluid diuresis started within 6 hours of ingestion is the key to survival. Peace lily and calla lily (Spathiphyllum, Zantedeschia) contain insoluble calcium oxalates and cause oral irritation, not renal failure — a classic exam distractor.

Grapes, Raisins, and Permethrin

Grapes and raisins cause idiosyncratic acute kidney injury in dogs (tartaric acid is the suspected toxic principle); treat with decontamination and 48 hours of IV fluids. Permethrin spot-on insecticides labeled for dogs cause life-threatening tremors and seizures in cats, which cannot metabolize the pyrethroid efficiently; management is methocarbamol for tremors, anticonvulsants, active cooling, bathing, and intravenous lipid emulsion for this lipophilic toxin.

Exam-Ready Toxin Summary