NAVLE Feline Pharmacology and Toxicology 6

Question 1

A 9-year-old DSH cat is diagnosed with oral squamous cell carcinoma and the oncologist considers platinum-based chemotherapy. A technician asks whether cisplatin can be dose-reduced for safer use in this cat. Which statement most accurately describes cisplatin use in cats?

Accepted Answer

Cisplatin is absolutely contraindicated in cats because it causes fatal pulmonary edema and pleural effusion regardless of dose

Answer

Cisplatin is absolutely contraindicated in cats at any dose. Unlike dogs and humans where the primary toxicities are nephrotoxicity and myelosuppression, cats develop fatal acute pulmonary edema and pleural effusion within hours to days of cisplatin administration due to species-specific capillary permeability responses. No dose reduction or supportive care protocol makes cisplatin safe in this species. Carboplatin is the preferred platinum-based alternative for feline oncology patients.

Question 2

A 6-year-old castrated male DSH is prescribed oral diazepam (1 mg PO BID) for urine marking behavior. On day 4, the owner reports acute lethargy, jaundice, and anorexia. ALT is 1,840 U/L and total bilirubin is 8.2 mg/dL. What is the most accurate characterization of this adverse reaction?

Accepted Answer

Idiosyncratic acute hepatic necrosis unique to cats receiving oral benzodiazepines, unrelated to dose or duration

Answer

Oral diazepam causes idiosyncratic acute hepatic necrosis in cats — a reaction that is unpredictable, not dose-dependent, and appears to be specific to the oral route. Affected cats can deteriorate rapidly within 2–5 days of initiating therapy. The mechanism is not fully elucidated but is not simply pharmacokinetic accumulation. IV diazepam carries much lower risk. This is why oral diazepam is generally contraindicated in cats, with alternatives such as gabapentin or environmental modification preferred for behavioral indications.

Question 3

A 4-year-old spayed DSH with phenobarbital-refractory epilepsy is started on potassium bromide (KBr) as add-on therapy. Eight weeks later she presents with progressive coughing, expiratory dyspnea, and eosinophilia (1,800 cells/µL). Thoracic radiographs reveal a diffuse bronchial-interstitial pattern. The most likely diagnosis is:

Accepted Answer

Potassium bromide–induced eosinophilic bronchopneumopathy

Answer

Potassium bromide causes eosinophilic bronchopneumopathy (EBP) in cats — a serious, species-specific adverse effect not observed in dogs. Clinical signs include coughing, dyspnea, and radiographic interstitial infiltrates with peripheral eosinophilia, typically developing weeks to months after initiation. This is distinct from feline asthma and resolves with KBr discontinuation. Because of this risk, KBr is generally avoided in cats; phenobarbital, levetiracetam, or zonisamide are preferred antiepileptic agents in this species.

Question 4

A 5-year-old cat with severe Mycoplasma haemofelis infection requires aggressive antibiotic therapy. The attending clinician wants to use enrofloxacin. Which of the following statements most accurately describes the risk-benefit consideration for enrofloxacin in this patient?

Accepted Answer

Retinal toxicity risk is substantially increased at doses exceeding 5 mg/kg/day; lesions typically occur within days and are irreversible

Answer

Enrofloxacin causes acute retinal degeneration (cone-rod degeneration leading to blindness) in cats in a dose-dependent manner. The FDA label restricts enrofloxacin in cats to a maximum of 5 mg/kg/day for this reason. Toxicity can occur within days of high-dose use and the photoreceptor damage is generally irreversible — vision loss is permanent once significant retinal degeneration has occurred. Lower doses are associated with acceptable risk, making dose precision critical. Doxycycline is frequently preferred for Mycoplasma haemofelis to avoid this risk.

Question 5

Cats develop more severe Heinz body hemolytic anemia from propylene glycol exposure than dogs given equivalent doses. Which mechanistic explanation best accounts for this species difference?

Accepted Answer

Feline hemoglobin contains approximately 8 reactive sulfhydryl groups per molecule — roughly twice as many as canine hemoglobin — making it disproportionately susceptible to oxidative denaturation

Answer

Feline hemoglobin is uniquely vulnerable to oxidative injury due to the greater number of reactive sulfhydryl (–SH) groups on its globin chains (~8 per molecule vs. ~4 in dogs). These free cysteine-associated sulfhydryl groups are readily oxidized, causing hemoglobin denaturation and Heinz body formation. This explains why cats are exquisitely sensitive to oxidant compounds — including propylene glycol, acetaminophen, benzocaine, onions, and methylene blue — that are tolerated at much higher doses in dogs. Propylene glycol was removed from cat foods specifically because of this risk.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Feline Pharmacology and Toxicology 6