NAVLE Feline Pharmacology and Toxicology 5

Question 1

A 4-year-old DSH cat is being treated for hyperthyroidism with methimazole. Three weeks into therapy, the owner notices the cat is scratching its face intensely and has developed periocular excoriations. CBC reveals eosinophilia. Which of the following is the most appropriate next step?

Accepted Answer

Discontinue methimazole, initiate radioactive iodine therapy or surgical thyroidectomy as definitive treatment

Answer

Facial pruritus and excoriations are a classic idiosyncratic adverse reaction to methimazole in cats, occurring in up to 20% of patients. Because carbimazole is converted to methimazole in vivo, cross-reactivity is nearly guaranteed, making it a poor alternative. Simply reducing the dose does not eliminate the antigen driving the reaction, and steroids would suppress but not resolve the underlying cause while allowing hyperthyroidism to continue. The correct approach is to discontinue methimazole entirely and pursue a definitive treatment — radioactive iodine (I-131) or surgical thyroidectomy — which resolves both the drug reaction and the underlying disease.

Question 2

A veterinarian prescribes enrofloxacin 5 mg/kg IV once daily for a 6-year-old cat with bacteremia. On day 3, the owner calls reporting the cat is bumping into objects and appears disoriented. Fundic examination reveals multifocal areas of retinal degeneration. What pharmacokinetic property of fluoroquinolones in cats most directly explains this toxicity?

Accepted Answer

Cats have reduced hepatic CYP1A2 activity, leading to accumulation of the parent compound

Answer

Cats have markedly reduced hepatic CYP1A2 (cytochrome P450 1A2) activity compared to dogs and humans. Enrofloxacin is primarily metabolized by CYP1A2 to ciprofloxacin. With impaired metabolism, the parent compound (enrofloxacin) accumulates to high plasma concentrations. Enrofloxacin — more so than ciprofloxacin — is directly retinotoxic in cats, causing acute retinal degeneration and blindness, especially at doses ≥5 mg/kg/day IV. The AVMA-recommended feline dose is ≤2.5 mg/kg/day to reduce this risk. Glucuronidation deficiency in cats is real but pertains to other drug classes (e.g., acetaminophen, aspirin), not fluoroquinolone toxicity.

Question 3

A 3-year-old spayed female cat presents in acute hepatic failure. The owner reports giving the cat an 'herbal flea remedy' containing pennyroyal oil topically two days ago. Serum chemistry reveals markedly elevated ALT, total bilirubin of 7.2 mg/dL, and prolonged PT. Which toxic mechanism best explains pennyroyal oil's hepatotoxicity in this patient?

Accepted Answer

Pulegone is bioactivated by CYP2E1 to a reactive electrophile (menthofuran and its epoxide) that depletes glutathione and causes covalent protein adducts

Answer

Pennyroyal oil is rich in pulegone, which undergoes hepatic bioactivation via CYP2E1 (and to a lesser extent CYP1A2) to form menthofuran and its reactive electrophilic epoxide intermediate. These metabolites rapidly deplete hepatic glutathione stores and form covalent adducts with cellular proteins, causing centrilobular (zone 3) hepatocellular necrosis. Cats are especially vulnerable because of their pre-existing deficiency in multiple conjugation pathways, reducing their capacity to detoxify reactive intermediates. N-acetylation deficiency is a known feline limitation but is not the primary mechanism here. Treatment parallels acetaminophen toxicosis: N-acetylcysteine (NAC) to replenish glutathione, along with supportive care.

Question 4

A 9-year-old cat with chronic kidney disease (CKD, IRIS Stage 3) and osteoarthritis requires long-term analgesia. Buprenorphine has provided insufficient pain control. Which analgesic option presents the HIGHEST risk of acute-on-chronic kidney injury in this patient and should be strictly avoided?

Accepted Answer

Meloxicam 0.1 mg/kg PO q24h as long-term maintenance

Answer

NSAIDs inhibit prostaglandin synthesis via COX enzymes. Prostaglandins are critical for maintaining afferent arteriolar dilation and glomerular filtration pressure in cats with CKD, where compensatory renal hemodynamics are already stressed. Long-term meloxicam use in CKD cats (especially IRIS Stage 3–4) poses a high risk of further reducing GFR and precipitating acute decompensation. While robenacoxib is also an NSAID, the short-course limitation (≤3 days) and its preferential local tissue distribution reduce systemic renal risk in CKD compared to chronic meloxicam. Gabapentin is renally excreted but is generally considered safe with dose adjustment in CKD, and low-dose ketamine CRI does not depend on prostaglandin-mediated renal perfusion. Chronic NSAID use in IRIS Stage 3+ CKD is contraindicated in cats.

Question 5

During a toxicology consult, you receive a call about a cat that ingested permethrin-containing dog spot-on approximately 1 hour ago. The cat is currently showing mild whole-body tremors and hypersalivation. The owner asks about inducing emesis at home with hydrogen peroxide. What is the most accurate and complete response?

Accepted Answer

Hydrogen peroxide is unreliable for emesis induction in cats and is contraindicated — instruct the owner to bring the cat in immediately for methocarbamol therapy and professional decontamination

Answer

Hydrogen peroxide is a dangerous and ineffective emetic in cats. Unlike dogs, cats do not reliably vomit in response to hydrogen peroxide, and it causes severe hemorrhagic gastroenteritis in this species. The appropriate feline emetics are dexmedetomidine (IM) or xylazine (IM/IV) administered by a veterinarian — never orally at home. Furthermore, although neurological signs are mild, the presence of tremors signals CNS involvement and increases aspiration risk with any emetic. The owner should immediately transport the cat for professional decontamination (bathing with dish soap to remove dermal permethrin), methocarbamol (muscle relaxant of choice for pyrethroid-induced tremors in cats), IV fluid support, and thermoregulation. Pyrethroids are not absorbed through the GI mucosa as efficiently as through skin, so dermal decontamination is the priority.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Feline Pharmacology and Toxicology 5