In December 2024, the FDA issued a “Dear Veterinarian Letter” to inform veterinarians of adverse events reported for dogs treated with bedinvetmab. Frontiers in Veterinary Science recently published a Zoetis-funded study titled Global pharmacovigilance reporting of the first monoclonal antibody for canine osteoarthritis: a case study with bedinvetmab (Librela), which presents adverse event reporting from more than 18 million doses administered globally.
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In this month’s lead story, Dr. Tamara Grubb, a diplomate of the American College of Veterinary Anesthesia & Analgesia, Certified Veterinary Pain Practitioner, and president of the International Veterinary Academy of Pain Management, offers insights on the study and the important takeaways for practitioners.
Let’s get to the bottom of this. Why was this warning letter released by the FDA?
Dr. Grubb: This letter is part of a normal FDA-guided process called “post-marketing surveillance,” and the release of letters like this is very common in all aspects of medicine, including veterinary medicine. Post-marketing surveillance is necessary because even robust clinical trials that lead to a drug’s approval for patient use cannot match the sheer numbers of patients that will receive that drug after it has been released for clinical use. That increase in number of patients often reveals adverse effects that were not revealed in clinical studies, that are uncommon, and/or that only occur in specific patients. A “Dear Healthcare Provider” letter is issued by the FDA when trends start to develop that the practitioner should be aware of that may, or may not, be related to a drug. The objective is to educate healthcare providers about effects to watch for and trends to monitor; it is not a condemnation of a drug nor a statement of cause and effect. (Potential cause and effect will be evaluated by the FDA if cases continue to emerge.) A good review of post-marketing surveillance is available here.
After reviewing this compilation of data, do you think the warning letter was warranted?
Dr. Grubb: The letter was absolutely warranted. It is a common occurrence at this stage of drug use. Also, Librela is a novel product so there are no data from similar drugs for comparison. We are still learning about anti-NGF monoclonal antibodies, and any information that we can garner is potentially very useful. Plus, one of the many tasks of the FDA is to ensure the safety of drugs and medical devices. Post-marketing surveillance data—as reported with warning letters—are a component of that mission.
The negative reaction to the letter was not warranted, in my opinion, and resulted from a misunderstanding of the intent of these letters. A warning letter is not a condemnation but rather an overview of potential post-launch effects and/or adverse effects, a caution to watch for trends. No cause/effect is proven at that point. The FDA clearly states that early reporting doesn’t prove cause/effect, and it is normal to see a relatively high incidence of reports when a drug is new and a large number of doses are distributed—18 million, in this case. To my knowledge, those numbers are unprecedented with veterinary medicine. With numbers like that, a more useful analysis would be a percentage of adverse effects based on the number of dogs treated rather than the absolute number of adverse effects, which might seem high but would most likely be a small percentage of the entire number treated.
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Considering this retrospective case study was authored/funded by Zoetis, what do you think is their responsibility in this situation?
Dr. Grubb: Every company has the responsibility to accurately present the effects, including adverse effects, of their drug to support efficacy and avoid complications for as many patients as possible. The data presented in this study are reported by veterinarians, and sometimes pet owners, which is similar to public data available through the FDA. Thus, the data are verifiable. Also, this is a peer-reviewed publication. Zoetis upheld their responsibility to accurately and transparently report the data.
What is the most important takeaway from this global case study that includes more than 18 million doses of bedinvetmab?
Dr. Grubb: In my mind, the most important takeaway for a practitioner treating dogs with osteoarthritis pain is that millions of dogs have been treated with bedinvetmab, and the incidence of adverse effects is very low. Every drug has adverse effects; but in my opinion, the adverse effects of not treating pain generally have bigger consequences than administering a drug to improve an animal’s quality of life. I think there is a quote that says something like, “To do nothing is to do harm.” That is very true with not treating animal pain. Experts, like those publishing AAHA, WSAVA and COAST guidelines, agree that bedinvetmab and NSAIDs are “first-choice” treatments for canine osteoarthritis pain. It is imperative that we learn from experts, which should help drown out non-scientific comments on social media. NSAIDs have adverse effects too, as indicated by the “Dear Doctor” letters that were issued for most, if not all, NSAIDs currently approved for dogs. The small likelihood of adverse effects has not pushed us to stop using NSAIDs globally, and it should not stop us from using bedinvetmab for the appropriate patient. In my opinion, any dog experiencing pain of osteoarthritis is potentially the right patient.
What should you know about the use of bedinvetmab as a general practitioner, and how should you communicate that to clients?
Dr. Grubb: To achieve maximum drug efficacy and gain client confidence, use a drug for what it has been proven to treat—osteoarthritis pain, in this case. As with all drugs, if a veterinarian thinks a drug isn’t the right choice for a certain patient, then the veterinarian shouldn’t use it in that patient. But, again, not treating pain at all is not the right choice for any patient. Talk to clients about potential adverse effects but also explain that a lot of supposed adverse effects are being reported on social media with no evidence that Librela is causing those effects. As professionals, it is important that we get our information from scientific sources and not from social media. And it is also important that we communicate scientific information to our clients.
Many of us have our own dogs on Librela, or have colleagues with dogs on Librela. Personal endorsement is often what clients need to feel comfortable. The magnitude of use of this drug, now almost 28 million doses distributed worldwide, is astounding. I am going to paraphrase a quote that I heard on a webinar from Dr. Duncan Lascelles, an osteoarthritis and Librela expert, who said that if Librela was going to cause a high percentage of adverse effects in the global dog population or commonly cause adverse effects that are of a greater magnitude than those currently reported, those adverse effects would have already been identified as a common occurrence.
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Is there anything you would like our readers to learn or know from this study that has not been mentioned?
Dr. Grubb: In my opinion, based on evidence, veterinarians and pet owners can trust bedinvetmab to be safe and effective for the majority of their canine patients with osteoarthritis pain. I remember the first analgesic the FDA approved for canine osteoarthritis pain, which was carprofen, specifically Rimadyl. We learned how to use that drug efficaciously and safely, and now we are learning the same about bedinvetmab.
Also, I tell colleagues to trust their caseload. Some referral patients may not be the right candidates for bedinvetmab because of advanced or complicated osteoarthritis or other underlying diseases. But for most on the frontline, I agree with the AAHA, WSAVA and COAST guidelines for pain management, which state that NSAIDs and anti-NGF monoclonal antibodies are first-line choices for pain relief for dogs with osteoarthritis pain.
And, again, fear of doing something wrong—meaning, doing nothing for a patient’s pain—is, in itself, wrong.
The Study
Global pharmacovigilance reporting of the first monoclonal antibody for canine osteoarthritis: a case study with bedinvetmab (Librela).
Monteiro BP, Simon A, Knesl O, et al. Front Vet Sci.
https://doi.org/10.3389/fvets.2025.1558222