NAVLE Feline Pharmacology and Toxicology 5 — Questions and Answers
Question 1: A cat receiving phenobarbital for seizure management develops a sudden increase in seizure frequency despite adequate serum levels. Which mechanism best explains this phenomenon?
- Phenobarbital induces its own metabolism via CYP450 induction, lowering effective blood levels over time
- GABA receptor downregulation develops with chronic phenobarbital use, reducing drug efficacy (Correct answer)
- Phenobarbital accumulates in adipose tissue and redistributes unpredictably
- Cats develop anti-phenobarbital antibodies after prolonged exposure
Correct answer: GABA receptor downregulation develops with chronic phenobarbital use, reducing drug efficacy
Chronic barbiturate use can cause GABA-A receptor downregulation and tolerance, reducing seizure threshold despite unchanged serum drug concentrations.
Question 2: Which drug is the first-line treatment for feline arterial thromboembolism (ATE) prevention?
- Warfarin
- Clopidogrel (Correct answer)
- Aspirin
- Heparin
Correct answer: Clopidogrel
Clopidogrel (Plavix) is superior to aspirin for secondary prevention of ATE in cats with cardiomyopathy, as demonstrated in the FAT CAT study.
Question 3: Propylene glycol is present in some semi-moist cat foods and medications. Why is it contraindicated in cats?
- It causes acute pancreatitis due to lipase inhibition
- It causes Heinz body formation and hemolytic anemia in cats (Correct answer)
- It is directly nephrotoxic through oxalate crystal deposition
- It causes hypernatremia by drawing water from red blood cells
Correct answer: It causes Heinz body formation and hemolytic anemia in cats
Cats are uniquely susceptible to propylene glycol-induced Heinz body hemolytic anemia because their hemoglobin contains eight SH groups versus four in dogs.
Question 4: A cat is presented for suspected oleander (Nerium oleander) ingestion. What is the primary mechanism of toxicity?
- Inhibition of Na+/K+-ATPase causing cardiac glycoside toxidrome (Correct answer)
- Cyanide-like inhibition of cellular cytochrome oxidase
- Muscarinic cholinergic receptor agonism
- Competitive inhibition of vitamin K epoxide reductase
Correct answer: Inhibition of Na+/K+-ATPase causing cardiac glycoside toxidrome
Oleandrin and neriine in oleander inhibit Na+/K+-ATPase, causing hyperkalemia, bradyarrhythmias, and AV block similar to digoxin toxicity.
Question 5: Which statement about maropitant (Cerenia) use in cats is correct?
- It is contraindicated in cats under 4 months of age
- It works by blocking D2 dopamine receptors in the chemoreceptor trigger zone
- It is approved at 1 mg/kg SC once daily for nausea prevention (Correct answer)
- It has no visceral analgesic properties in cats
Correct answer: It is approved at 1 mg/kg SC once daily for nausea prevention
Maropitant is approved at 1 mg/kg SC in cats for nausea and vomiting; it blocks NK1 receptors and also provides visceral analgesia.
Question 6: A cat is diagnosed with feline infectious peritonitis (FIP). Which antiviral drug has shown efficacy and received conditional FDA approval for this disease?
- Famciclovir
- GS-441524 (Correct answer)
- Interferon omega
- Oseltamivir
Correct answer: GS-441524
GS-441524, an adenosine nucleoside analog, inhibits feline coronavirus RNA-dependent RNA polymerase and has conditional FDA approval as Mutian/brand equivalents for FIP.
Question 7: A hyperthyroid cat on methimazole develops a platelet count of 40,000/µL on a CBC. What is the most appropriate next step?
- Continue methimazole and recheck CBC in 2 weeks
- Reduce the methimazole dose by 50%
- Discontinue methimazole immediately and consider radioactive iodine or surgical thyroidectomy (Correct answer)
- Add prednisone to counteract methimazole-induced immune suppression
Correct answer: Discontinue methimazole immediately and consider radioactive iodine or surgical thyroidectomy
Severe thrombocytopenia is a serious hematologic adverse effect of methimazole requiring immediate discontinuation; alternative definitive therapies should be pursued.
NAVLE Feline Pharmacology and Toxicology 5
A cat receiving phenobarbital for seizure management develops a sudden increase in seizure frequency despite adequate serum levels.
Which mechanism best explains this phenomenon?