NAVLE Feline Pharmacology and Toxicology Questions and Answers — Questions and Answers
Question 1: A 2-year-old indoor cat is presented to the emergency clinic with acute onset of vomiting, lethargy, and anorexia. The owner recently received a floral arrangement containing lilies. On physical examination, the cat is dehydrated and has painful kidneys on palpation. Bloodwork reveals severe azotemia. Which of the following is the most critical initial treatment for this suspected toxicity?
- N-acetylcysteine administration
- Administration of activated charcoal and a cathartic
- Intravenous fluid diuresis (Correct answer)
- Peritoneal dialysis
Correct answer: Intravenous fluid diuresis
Ingestion of any part of a lily plant (Lilium or Hemerocallis species) can cause severe, acute renal failure in cats. The primary mechanism is acute tubular necrosis. The cornerstone of treatment is aggressive intravenous fluid therapy to support renal perfusion, promote diuresis, and flush out the unknown nephrotoxin. While decontamination with activated charcoal is useful if ingestion was very recent, fluid therapy is the most critical life-saving intervention once clinical signs have developed. N-acetylcysteine is the antidote for acetaminophen toxicity, and peritoneal dialysis is reserved for anuric patients unresponsive to fluid therapy.
Question 2: A cat is accidentally administered a dose of acetaminophen (paracetamol). Which clinical sign is most characteristic of this specific toxicity in felines due to their metabolic differences?
- Severe gastrointestinal ulceration
- Methemoglobinemia and facial edema (Correct answer)
- Acute fulminant hepatic necrosis
- Profound coagulopathy
Correct answer: Methemoglobinemia and facial edema
Cats have a deficiency in the glucuronidation pathway, a major route for acetaminophen metabolism in other species. This shunts metabolism down alternative pathways, leading to the production of toxic metabolites that cause oxidative damage to red blood cells. This results in the formation of methemoglobin, which cannot carry oxygen, leading to cyanosis (often described as 'muddy' or brown mucous membranes), dyspnea, and often concurrent facial or paw edema. While liver damage can occur, methemoglobinemia is the more prominent and life-threatening feature in cats.
Question 3: A 12-year-old cat diagnosed with hyperthyroidism is started on oral methimazole. Within the first three weeks of treatment, the owner reports the cat is scratching its face and neck incessantly, causing excoriations. Which of the following is the most appropriate action?
- Decrease the dose of methimazole by half and recheck in one week.
- Add a glucocorticoid to the treatment regimen to control the pruritus.
- Switch to the transdermal formulation of methimazole.
- Discontinue methimazole and discuss alternative treatments like radioiodine (I-131) therapy. (Correct answer)
Correct answer: Discontinue methimazole and discuss alternative treatments like radioiodine (I-131) therapy.
Severe facial pruritus and excoriation is an uncommon but serious idiosyncratic adverse reaction to methimazole in cats. It is considered an immunologic reaction and will not resolve by lowering the dose and is likely to recur with any formulation of the drug, including transdermal. The appropriate response is to stop the drug immediately and manage the pruritus. An alternative therapy for hyperthyroidism, such as radioiodine (I-131) or a prescription diet, must be chosen as the cat cannot tolerate methimazole.
Question 4: A cat presents with acute onset of severe muscle tremors, hyperthermia, and mydriasis after the owner applied a canine-specific flea and tick spot-on product. Which of the following toxicities is most likely, and what is the primary therapeutic agent used to control the tremors?
- Organophosphate toxicity; Atropine
- Ethylene glycol toxicity; Fomepizole
- Permethrin toxicity; Methocarbamol (Correct answer)
- Ivermectin toxicity; Intralipid emulsion
Correct answer: Permethrin toxicity; Methocarbamol
The clinical signs described are classic for permethrin toxicity, which occurs when concentrated canine flea products containing this pyrethroid are applied to cats. Cats are deficient in the enzymes needed to metabolize permethrin effectively. The primary treatment for the resulting muscle tremors and fasciculations is the centrally-acting muscle relaxant, methocarbamol. Atropine is for organophosphate toxicity, fomepizole for ethylene glycol, and intralipid emulsion is an adjunctive therapy for lipid-soluble toxins like ivermectin.
Question 5: Amlodipine is the first-line treatment for systemic hypertension in cats. What is its primary mechanism of action?
- Angiotensin-converting enzyme (ACE) inhibition
- Beta-adrenergic receptor blockade
- Calcium channel blockade (Correct answer)
- Alpha-adrenergic receptor antagonism
Correct answer: Calcium channel blockade
Amlodipine is a dihydropyridine calcium channel blocker. Its primary effect is to block the influx of calcium into vascular smooth muscle cells, which leads to peripheral vasodilation and a subsequent decrease in systemic blood pressure. ACE inhibitors (like benazepril), beta-blockers (like atenolol), and alpha-antagonists (like prazosin) are other classes of antihypertensive drugs with different mechanisms of action.
Question 6: Which of the following best describes the primary mechanism by which non-steroidal anti-inflammatory drugs (NSAIDs) can induce acute kidney injury in a cat that is dehydrated or hypotensive?
- Direct nephron apoptosis via oxidative damage
- Inhibition of prostaglandin-mediated renal vasodilation (Correct answer)
- Formation of obstructive crystals within the renal tubules
- Immune-mediated glomerulonephritis
Correct answer: Inhibition of prostaglandin-mediated renal vasodilation
In states of decreased renal perfusion (like dehydration or hypotension), the kidneys rely on locally produced prostaglandins (PGE2 and PGI2) to cause afferent arteriole vasodilation, which maintains glomerular filtration rate (GFR). NSAIDs inhibit cyclooxygenase (COX) enzymes, thereby blocking prostaglandin synthesis. This inhibition prevents the compensatory vasodilation, leading to a profound reduction in renal blood flow, decreased GFR, and potential ischemic acute tubular necrosis.
NAVLE Feline Pharmacology and Toxicology Questions and Answers
A 2-year-old indoor cat is presented to the emergency clinic with acute onset of vomiting, lethargy, and anorexia.
The owner recently received a floral arrangement containing lilies.
On physical examination, the cat is dehydrated and has painful kidneys on palpation.
Bloodwork reveals severe azotemia.
Which of the following is the most critical initial treatment for this suspected toxicity?