Pharmacology and Toxicology Flashcards

A 6-year-old male neutered Border Collie is presented with acute onset of seizures, ataxia, and apparent blindness. The owner reports the dog may have ingested a medication from the barn used to deworm sheep. Which of the following drugs is the most likely cause of these clinical signs?

Answer: Ivermectin

Ivermectin toxicity is common in herding breeds, like Border Collies, that have a mutation in the MDR1 (multi-drug resistance 1) gene. This mutation allows ivermectin to cross the blood-brain barrier, leading to severe neurologic signs such as seizures, ataxia, and blindness. The other listed dewormers have a much wider margin of safety and do not typically cause neurotoxicity at standard doses.

A client calls in a panic stating their 2-year-old cat just ingested several acetaminophen (500 mg) tablets. Which of the following clinical signs and laboratory findings is most characteristic of acetaminophen toxicity in this species?

Answer: Methemoglobinemia, facial edema, and hepatic necrosis

Cats are highly susceptible to acetaminophen toxicity due to a deficiency in the glucuronidation pathway for metabolism. This leads to the formation of toxic metabolites that cause oxidative damage to red blood cells, resulting in methemoglobinemia (chocolate-colored blood and mucous membranes), and severe liver damage (hepatic necrosis). Facial and paw edema are also classic signs. The antidote is N-acetylcysteine (NAC).

Which of the following is the primary mechanism of action for non-steroidal anti-inflammatory drugs (NSAIDs) like carprofen and meloxicam?

Answer: Inhibition of cyclooxygenase (COX) enzymes

NSAIDs exert their anti-inflammatory, analgesic, and antipyretic effects by inhibiting cyclooxygenase (COX) enzymes. This inhibition reduces the production of prostaglandins, which are key mediators of inflammation, pain, and fever.

A horse is being treated with gentamicin, an aminoglycoside antibiotic, for a severe bacterial infection. Which of the following potential toxicities is the most significant concern with this class of drug and requires therapeutic monitoring?

Answer: Nephrotoxicity

The primary adverse effect of aminoglycoside antibiotics, such as gentamicin and amikacin, is nephrotoxicity (kidney damage). Ototoxicity (damage to the ear) is also a concern. Monitoring renal function through bloodwork (BUN, creatinine) is crucial during therapy to prevent irreversible kidney damage.

A dog presents with signs of severe coagulopathy, including epistaxis and melena, 4 days after potentially ingesting a rodenticide. Which of the following is the most likely active ingredient in the rodenticide and the most appropriate antidote?

Answer: Brodifacoum; Vitamin K1

Anticoagulant rodenticides, such as brodifacoum, inhibit the enzyme Vitamin K epoxide reductase, which is essential for activating clotting factors II, VII, IX, and X. This leads to a severe bleeding disorder. The direct antidote is supplementation with Vitamin K1 (phytonadione) for several weeks to allow the body to produce new clotting factors.

What is the primary reason for avoiding the use of fluoroquinolone antibiotics (e.g., enrofloxacin) in young, growing puppies?

Answer: Adverse effects on the development of articular cartilage

Fluoroquinolone antibiotics have been shown to cause damage to developing articular cartilage (arthropathy) in young, growing animals, particularly dogs. This can lead to erosions in the cartilage of weight-bearing joints. For this reason, their use is contraindicated in puppies, especially of large and giant breeds.