Trifexis debate...

The discussions about Trifexis

We've had this question asked several times since the new stories and sensationalizations were made on FaceBook. There are several big picture topics to address with this and I don't think Facebook will give me enough room to write it all out! Here are the basics:

Part 1: Where was the preventative purchased... The FDA released a brochure about cautions in where you purchase medications:

http://www.fda.gov/ForConsumers/consumerUpdates/ucm048164.htm or http://www.fda.gov/downloads/ForConsumers/ConsumerUpdates/ucm115432.pdf.

Part 2: Giving heartworm preventatives to dogs who are positive for heartworms can kill them... regardless of the brand of the medication. The preventatives kill the baby microfilaria and in a heartworm negative dog who has been exposed through mosquitos the circulating numbers of microfilaria are low so killing them all at the same time is manageable for the body. BUT... in a heartworm positive dog there can be a LARGE quantity of microfilaria and if they all die at the same time it can create a shock reaction to the body (anaphylaxis) and/or they can clog capillary beds and act like blood clots all over the body. It is VERY important to have YEARLY heartworm tests performed in order to ensure safety in giving ANY of the heartworm preventatives and give them preventatives ONCE A MONTH, EVERY MONTH, ALL YEAR AROUND!

Part 3: All of the preventatives have been tested for safety. Typically 5-10 times the normal dose range (as you can imagine a dog chewing into a 6 pack of the prevention and eating all of it at one time). Specifically for Trifexis, it was tested at 5 times the therapeutic dose and they had vomiting as the most significant clinical sign (6%). The most significant signs seen from the testing was salivation, tremors, and lethargy. We've sold over 2200 doses since we've started carrying it and they only signs we've seen were reluctance to take the tablet and vomiting. I've talked with several vets who have sold over 100,000 doses with no more clinical signs than we've seen.

Part 4: Complete physical examinations with great communication and conversation with your veterinarian is vitally important.  It is our number 1 priority in preventative health care.  This allows the team (you and the owner and the veterinarian) to determine if there are any concerns in giving medications (any medications, not just heart worm preventatives), what types are safe and which may not be, and how to provide the best care you can for your pet.  Our second priority in preventative health care is diagnostic testing. Simply looking at a heart worm test is the start and annual testing is necessary for a variety of reasons. Blood work testing for other organ system (liver, kidneys, pancreas, etc.) conditions, urine testing, and x-rays help to give your doctor the most complete understanding of how the body is working on the inside, especially since subclinical disease could be lurking and it is not visible on the outside. If there is a structural (heart thickening or enlargement for example) or physiological (liver failure, kidney insufficiency, etc.) conditions it may create adverse effects with any number of medications (not just Trifexis).

From the news reports: There simply is not enough information to give any sincere opinion other than what has been said. Owners with concerns are reporting their issues to the FDA, the FDA wouldn't allow a medication that would be causing severe complications including death to stay on the market for any length of time, and the concerns are being investigated. You may not know or remember that there was a 6 month injectable heartworm preventative removed from the market when around 500 dogs died after receiving the medication. We are not seeing any of the medical records, lab work results, or pathology reports to determine independently what happened and as such what I read says we should be monitoring the situation and talking to clients about risk of ALL medications (as we do). It would be foolish to believe that medications wouldn't be a cause for issues in the body. As true in human medicine, side effects are always listed (even if the drug wasn't the cause) and people and pets can have reactions to ANY medication at any time. If there is a real problem it will be identified.

This is a great time to reiterate these important points: 1. Get your pets to the vet regularly and have a solid relationship with lots of communication. We want to not just inform, but to teach you about medicine, preventative care, etc. YOU the client need to be involved, informed, and learn about your pet's health. 2. Get diagnostics performed that meet or exceed the acceptable standard of care. Heartworm testing YEARLY has been recommended by the Heartworm Society and the Companion Animal Parasite Council for several years now. Pets need blood work, fecal/stool tests, urine tests, radiographs, etc. on a regular basis like we do. An older pet may have liver disease or cancer that can adversely react to a medication like Trifexis, but complications get blamed on the medication. 3. Give your pets prevention once a month, every month, all year around. 4. Get your prevention from TRUSTED sources and your veterinarian will know who he/she can trust (it isn't just at the clinic, we do have an online pharmacy or two we can trust).

Thank you so much for bringing up this topic to address. We always enjoy talking about issues regarding pets, helping to provide balance and understanding where needed, and most of all education and information to help make the lives of our pets healthier, longer!

If you have a question or pet-related topic for Dr. Schenck to discuss in an upcoming article, email it to 


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