Why a 15 kg Collie reacts differently to ivermectin than larger breeds
Smaller dogs like your Collie are more vulnerable to ivermectin overdose because their body weight affects how quickly the drug is metabolized. Even if the dose was only slightly over the recommended amount, his size means the concentration in his bloodstream could still be high enough to cause neurological symptoms. The vet will be particularly cautious about monitoring his recovery timeline compared to a heavier dog.
Breeds with certain genetic traits (like some herding dogs) can also be extra sensitive to ivermectin, which is why your vet is watching for tremors or dilated pupils even after initial treatment. These signs would show the drug is still affecting his nervous system, requiring extended care.
Blood tests that track ivermectin's path through his body
The liver and kidney panels your vet runs aren't just routine—they're looking for two specific things. First, whether his liver enzymes show strain from breaking down the ivermectin, which could mean slower drug clearance. Second, if his kidneys are properly filtering the byproducts, since dehydration from vomiting or lack of appetite can complicate recovery.
Expect these tests to be repeated every 12-24 hours initially, as the levels can change rapidly. If his earlier overdose caused vomiting or diarrhea, electrolyte checks will also be frequent to prevent secondary issues like muscle weakness or irregular heart rhythms.
Neurological checks you might see the vet perform
During visits, the vet will test his reflexes, pupil reactions, and coordination—like having him walk in a straight line or step over low objects. These aren't just for severe symptoms; subtle changes like slightly delayed blinking or a wider stance can signal that ivermectin is still active in his system at low levels.
You'll get instructions to watch for specific behaviors at home too, such as whether he startles at noises normally or struggles with stairs. Collies often show neurological effects earlier than other breeds, so your observations help adjust his recovery plan.
What supportive care looks like after the first 48 hours
If he's stable but not yet back to normal, the vet might switch from IV fluids to subcutaneous ones or recommend small, frequent meals to support liver function without overwhelming him. They'll likely keep him on a bland diet longer than usual, since his digestive tract may still be sensitive from the overdose.
Recovery isn't linear—some dogs have days where they seem better, then show mild tremors after exertion. Your vet will prepare you for this possibility and may schedule follow-up blood work a week later to confirm his organs have fully rebounded.
The step-by-step response, from the first minute to the vet visit, is in our Heartworm Preventative Overdose emergency guide.