NAVLE Toxicology: Common Poisons, Mechanisms & Antidotes

Toxicology shows up on roughly 5–8% of the NAVLE. That is 18–28 questions out of 360. Most of it clusters around 15–20 toxins that rotate through exams year after year. Know these cold and you are not leaving points on the table.

How Toxicology Appears on the NAVLE

The exam hits toxicology in three ways. First: a dog or cat presents with clinical signs and you have to name the toxin. Second: the toxin is named and you pick the antidote or explain the mechanism. Third: species-specific susceptibility—which animal cannot handle this exposure. Each type requires a different knowledge layer, and the fastest way to get all three right is to organize your learning by mechanism rather than by toxin name.

Top Toxins by Mechanism

Category 1: Cholinesterase Inhibitors — Organophosphates & Carbamates

These are the classic farm and insecticide toxins. Organophosphates (chlorpyrifos, malathion, diazinon) and carbamates (carbaryl, methomyl) both inhibit acetylcholinesterase, letting acetylcholine pile up at every synapse it touches. The clinical result is the SLUD syndrome: salivation, lacrimation, urination, defecation. Add miosis, bradycardia, and bronchospasm on the muscarinic side; muscle fasciculations and weakness on the nicotinic side.