NAVLE Feline Pharmacology and Toxicology 4 — Questions and Answers
Question 1: Which antiparasitic drug has a narrow safety margin in cats and can cause mydriasis, ataxia, tremors, and death if overdosed, particularly in debilitated individuals?
- Praziquantel
- Selamectin
- Ivermectin (Correct answer)
- Fenbendazole
Correct answer: Ivermectin
Ivermectin toxicity in cats causes CNS signs by enhancing GABA-mediated inhibition; cats lack MDR1 mutation but are still sensitive to overdose.
Question 2: Gabapentin is increasingly used in cats for anxiety and pain. Which pharmacokinetic property is clinically important in feline dosing?
- It undergoes extensive first-pass hepatic metabolism
- It is renally excreted unchanged and dose must be reduced with renal insufficiency (Correct answer)
- It is highly protein-bound and interacts with NSAIDs
- It requires CYP2D6 for activation to its active form
Correct answer: It is renally excreted unchanged and dose must be reduced with renal insufficiency
Gabapentin is eliminated renally with minimal hepatic metabolism, so dose intervals must be extended in cats with chronic kidney disease.
Question 3: A cat presents comatose after ingesting ethylene glycol. Which diagnostic finding would confirm ethylene glycol toxicity?
- Presence of uric acid crystals in urine sediment
- Calcium oxalate monohydrate crystalluria (Correct answer)
- Hypocalcemia with prolonged QT interval on ECG
- Elevated blood ammonia with hepatic encephalopathy
Correct answer: Calcium oxalate monohydrate crystalluria
Ethylene glycol is metabolized to oxalic acid, which combines with calcium to form calcium oxalate monohydrate crystals visible in urine sediment.
Question 4: Which statement about the use of doxycycline in cats is most accurate?
- Liquid or food must accompany doxycycline administration to prevent esophageal stricture (Correct answer)
- Doxycycline is contraindicated in cats under 6 months due to bone growth plate damage
- Cats require twice the canine mg/kg dose due to faster hepatic clearance
- Subcutaneous injection of doxycycline is preferred over oral administration
Correct answer: Liquid or food must accompany doxycycline administration to prevent esophageal stricture
Doxycycline pills lodged in the feline esophagus cause chemical strictures; always follow tablets with food or water, or use liquid formulations.
Question 5: A cat develops bradycardia and hypotension following topical application of an ophthalmic timolol solution. What is the mechanism of this adverse effect?
- Direct myocardial toxicity of the benzalkonium chloride preservative
- Systemic absorption of the beta-blocker through the nasolacrimal duct (Correct answer)
- Activation of the oculocardiac reflex by the drops
- Alpha-1 agonist activity at cardiac receptors
Correct answer: Systemic absorption of the beta-blocker through the nasolacrimal duct
Timolol is absorbed systemically via the nasolacrimal duct in cats, exerting beta-1 blockade effects on heart rate and blood pressure.
Question 6: Which toxin from Rhododendron spp. causes salivation, vomiting, bradycardia, and hypotension in cats by activating sodium channels?
- Grayanotoxin
- Taxine
- Andromedotoxin
- Andromedotoxin and grayanotoxin are the same compound (Correct answer)
Correct answer: Andromedotoxin and grayanotoxin are the same compound
Grayanotoxin and andromedotoxin are synonymous names for the same sodium channel-activating diterpene in Rhododendron/Azalea plants.
Question 7: A veterinarian wants to use tramadol for postoperative analgesia in a cat. Which metabolic difference limits tramadol's efficacy in cats compared to humans?
- Cats rapidly glucuronidate tramadol into an inactive metabolite
- Cats have reduced CYP2D6 activity and produce very little O-desmethyltramadol (M1), the active opioid metabolite (Correct answer)
- Cats excrete tramadol unchanged in bile, reducing systemic exposure
- Cats over-express mu-opioid receptors, making them hypersensitive to tramadol
Correct answer: Cats have reduced CYP2D6 activity and produce very little O-desmethyltramadol (M1), the active opioid metabolite
Cats have low CYP2D6 activity and generate minimal M1 metabolite, so tramadol's analgesic effect via opioid receptors is substantially reduced.
NAVLE Feline Pharmacology and Toxicology 4
Which antiparasitic drug has a narrow safety margin in cats and can cause mydriasis, ataxia, tremors, and death if overdosed, particularly in debilitated individuals?