From the Trifexis website: “Serious adverse reactions have been reported following concomitant extra-label use of ivermectin with spinosad alone, one of the components of Trifexis chewable tablets.
Treatment with fewer than three monthly doses after the last exposure to mosquitoes may not provide complete heartworm prevention. Prior to administration of Trifexis, dogs should be tested for existing heartworm infection. Use with caution in breeding females. The safe use of Trifexis in breeding males has not been evaluated. Use with caution in dogs with pre-existing epilepsy.
The most common adverse reactions reported are vomiting, depression/lethargy, itching, decreased appetite, and diarrhea. To ensure heartworm prevention, observe your dog for one hour after administration. If vomiting occurs within an hour of administration, redose with another full dose. Puppies less than 14 weeks of age may experience a higher rate of vomiting.”
From Elanco: “In the United States alone about 70 million doses of Trifexis have been dispensed and 15,000 veterinary clinics rely on the product. Elanco and the FDA conduct continuous, on-going monitoring on Trifexis, and all products, to determine if there are any signals or trends in the data, any increases in frequency of certain types of reports, etc.
The FDA states : “FDA is aware of adverse event reports in connection with Trifexis and continues to closely monitor them. It is very important to realize that reports of adverse events do not necessarily mean that the product caused the event. Other factors, such as existing disease, exposure to chemicals or contaminants, foods, or other medications may have triggered or contributed to the cause of the event. However, when FDA is able to establish a safety concern with an approved animal drug, it may take actions such as requesting the manufacturer changes the label to reflect this safety issue and provides information to veterinarians and animal owners about how to use the product more safely. FDA is reviewing all available information on Trifexis in order to determine if actions such as label changes need to be taken. ”