#1: Authorship is a big one, and the conflict of interest developing during the review process shows that these are not disinterested researchers.
#2: The type of study is a nearly worthless type, in that it has no real statistical control and is just asking people to report on things on the internet. What ends up happening with these studies is that people self-recruit by word of mouth. Survey respondents may have been asked by other participants to register adverse events, and survey respondents may have never given the medication to a pet or seen an adverse event. There is no controlling for that apparent in the study.
#3: The survey instrument is supposed to be in the appendix and it is not, yet it is not described. Their recruitment process is described only as "distributed electronically by mail throughout the United States to veterinarians, veterinary clients, pet caregivers/owners, kennel club groups and on social media sites between August 1 and 31, 2018." There are lots of complaints about the adverse-event reporting system, the worst is that adverse events are merely enumerated from reports and there is no real way to put them into a statistical study. This is just getting another enumeration of events and putting a different denominator under them.
In my prescribing I have seen only one adverse event worth reporting: a dog was heartworm positive and received ivermectin, doxycycline and afoxolaner at the same time. It had a transient episode of low blood pressure treated with fluids. For a drug that, in their denominator, gives 80+% adverse reactions, that is very surprising. So, the study doesn't really pass the smell test.
There have been other drugs that have caused adverse reactions in significant numbers of patients. We stop using them immediately. The difference is very noticeable.
