I just saw about a dog with very dilated pupils at a vets office after it ate ivermectin horse wormer that a horse slobbered out and didn't swallow, it was a herding breed dog like aussie, heeler or birder collie and apparently these dogs in particular have serious hypersensitivity to ivermectin that can be fatal so do not use it for heartworm on dogs like those. If a mutt that has the blue merle type markings it probably has that breed mixture.
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I have heard that before but Heartgard is Ivermectin so it's confusing to me.
https://www.drugs.com/pro/heartgard-plus.html
"Heartgard Plus has been shown to be bioequivalent to HEARTGARD, with respect to the bioavailability of ivermectin. The dose regimens of Heartgard Plus and HEARTGARD are the same with regard to ivermectin (6 mcg/kg). Studies with ivermectin indicate that certain dogs of the Collie breed are more sensitive to the effects of ivermectin administered at elevated dose levels (more than 16 times the target use level) than dogs of other breeds. At elevated doses, sensitive dogs showed adverse reactions which included mydriasis, depression, ataxia, tremors, drooling, paresis, recumbency, excitability, stupor, coma and death. HEARTGARD demonstrated no signs of toxicity at 10 times the recommended dose (60 mcg/kg) in sensitive Collies. Results of these trials and bioequivalency studies, support the safety of HEARTGARD products in dogs, including Collies, when used as recommended.
Heartgard Plus has shown a wide margin of safety at the recommended dose level in dogs, including pregnant or breeding bitches, stud dogs and puppies aged 6 or more weeks. In clinical trials, many commonly used flea collars, dips, shampoos, anthelmintics, antibiotics, vaccines and steroid preparations have been administered with Heartgard Plus in a heartworm disease preventive program.
In one trial, where some pups had parvovirus, there was a marginal reduction in efficacy against intestinal nematodes, possibly due to a change in intestinal transit time."
According to the horse product I have on hand at the house, they get dosed at a rate of 200mcg/kg (so that's more than 33x what the dogs are getting), and if the dog managed to get close to a full syringe worth, that horse dose is target at 1250lbs.
So for a fairly large dog (say 50lb), we'd have 1250/50=25, and that would be 25 * 33 = 825x the recommended potency that dog lapped up!
Our cat Sally takes Sallymectin. Maybe they just need a more targeted medication.
https://www.petco.com/shop/en/petcostore/product/revloution-topical-solution-for-cats-51-15-lbs-blue
*Border collie