The first place to look for issues of safety or efficacy is USDA. IIRC they regulate equine medications. I don’t know if FDA is involved in this or not. There are some drugs that are used in humans and horses (sulfamethoxazole is an example). So there may be overlapping regulation.
In any event the regulatory agency that approved the product maintains a data base of adverse reactions. Find the agency that approved Quest and look for that data base.
Be aware that the information there is of mixed quality. You’ll find reports from teaching vet. hospitals and from individual owners. Don’t jump to the conclusion that every negative report is reliable 'cause it’s not. Post hoc ergo propter hoc conclusions abound.
I’ve used Quest in more than 100 different horses (mine and boarders) over the years and never had a bad reaction. I always read the label and follow the dosing recommendations.
All drugs carry a risk of adverse reaction. This is “meat on the table” for anti-science, “natural” crowd that will scream and holler loudly if an adverse reaction occurs. That it happens once in 10,000 uses (or some similar number) will be quietly ignored.
BOGO was also found to have some EPM exposure, and while we can’t always know when a horse is being affected, we already know that ivermectin and moxidectin should not be given to EPM horses. I highly doubt his owner would be railing against ivermectin if this had happened after using that. Quest is a great scapegoat for a lot of people.
You’re right, these ARE poisons. They are poisons developed to work against a parasite’s physiology, not a mammal’s. They cross the blood-brain barrier that parasites have, but are designed not to for mammals. It does very occasionally happen, particularly when that barrier is already compromised, aka EPM.
But like ALL things that aim at killing or healing or preventing or mitigating, there is always the potential for individuals to be in the fringes of highly adversely affected. Every scientist knows that. Research takes that into account, and all good research stops when there is a too-high level of adverse reactions. Approvals look at those statistics, and won’t approve anything that has a currently known too-high risk for the general population.
I’ve used Quest on a horse with a 1500 FEC - he didn’t bat an eye. Of the 100s of 1000s of uses of moxidectin since it came out, the number of issues is a very small %. I’d be willing to bet that most of those came in the earlier days, when everyone jumped on this “magic” product and used it on everything, including those with high worm loads, and there were impaction colics, or just general ADR due to large die-offs. There was also an issue with the plunger lock not locking, so some horses got too much (the small horses, and ponies).
Far too many people personally affected by something like this always and only look to the most recent thing done, and assume that correlation = causation. That is a dangerous assumption. The “West Nile vaccine causes abortions” fanatics were no different - zero causation. A lot of people jumped on the bandwagon of vaccines causing abortions when there was a rash of abortions in KY however many years ago - proven to be a totally unrelated cause that was simply not obvious to those who blamed the act they could see.
