Anima Books
books by holistic veterinarian Dr Christine King
Miscellany
The trouble with Librela and Solensia
These arthritis drugs are not as good as they sound
In an earlier article, I wrote about a simple pain indicator checklist for cats, the Feline Osteoarthritis (OA) checklist.
In it, I mentioned the drug Solensia™, which is a synthetic antibody product designed to target nerve growth factor in cats as a way of managing the pain of osteoarthritis. Librela™ (Beransa™ in Australia) is the canine version of the same thing.
In case it seemed as though I'm for this approach, I want to make it clear that, in my considered opinion, this entire class of drug — indeed, the whole biochemical approach to degenerative joint disease — is hopelessly flawed, and I do not recommend this drug class for any animal.
One of my favorite philosophers is the rather impish and iconoclastic British theologian, Alan Watts. Of the many wonderful things he said, here is one of my favorites:
“We cut things up into little pieces
and then declare that they are made out of pieces.”
Nowhere is this more true than in conventional medicine, and particularly the molecular biology that underpins its fragmented approach to bodies.
In fact, 'molecular biology' is an oxymoron, given that biology is the study of living things — i.e., whole things.
In focusing, to the exclusion of all else, on one molecule or biochemical pathway, we are failing to see the forest for the flea on the beetle on the leaf of a single tree.
I've been following the veterinary literature on this drug class for awhile now, and I've been listening in as small animal vets discuss their experiences with the drugs, both good and bad. Following is a summary for your consideration.
First, the acronyms:
MAB — monoclonal antibody
In this context, it's a synthetic antibody designed to target a specific molecule.
Synthetic monoclonal antibodies tend to have names that end in -mab. For example, Solensia is frunevetmab, Librela and Beransa are bedinvetmab, and the ill-fated human version (see below) is tanezumab.
NGF — nerve growth factor
The target of the MABs in Solensia, Librela, and Beransa is NGF.
Put another way, these drugs are called anti-NGF therapy.
OA — osteoarthritis; degenerative joint disease with bony changes
And now for my summary of the problems with these drugs.
1. These products are not approved for human use, and with good reason
These drugs were first tried in humans with OA, following lab animal studies. For example, tanezumab, which is a synthetic monoclonal antibody (MAB) product targeting nerve growth factor (NGF), was developed for use in humans based on a mouse model. In fact, tanezumab is described as a “humanized” form of a mouse anti-NGF MAB.
In 2021, the US Food and Drug Administration (FDA) voted against its licensure. After due deliberation, the panel overwhelmingly concluded that the proposed 'risk evaluation and mitigation strategy' offered by the manufacturer was insufficient to ensure that the drug's benefits outweigh its risks. The vote wasn't even close: 19 to 1 against its approval.
Later that same year, the European Medicines Agency likewise voted against the drug's authorization for use in the European Union.
In 2022, a systematic review examined the results of six randomized, controlled clinical trials of anti-NGF MAB products in humans. The goal was to compare the safety and efficacy of these products against other, established treatments — specifically, nonsteroidal anti-inflammatory drugs and oxycodone (a synthetic opioid) — in the management of pain associated with OA of the hip or knee.
Note that this study compared the anti-NGF MAB products with active treatment, not with a placebo.
Two key findings might well have sunk this entire drug class for good — in every sense (permanently, and for the better).
In the patients treated with an anti-NGF MAB product, there was a significantly higher incidence of:
* abnormal peripheral sensation (pain, tingling, numbness, etc.), indicating peripheral neuropathy, or pathology involving the nerves
* rapidly progressive OA, leading in some cases to the need for total joint replacement
There were numerous other adverse effects documented in these clinical trials, but peripheral neuropathy and rapid progression of OA were statistically the most compelling.
2. These products work miracles — except when they don't
These products seem to work wonders in some animals — at least for a time.
One of the documented 'adverse events' in animals is loss of effectiveness with repeated doses. One of the possible reasons is the development of natural antibodies against the synthetic MAB. Ironic. Other possible reasons include progression of established OA, development of new lesions in other joints or tissues, and neurologic disorder.
But in other animals, the results from the outset range from no effect (complete waste of money) to death, typically following a long and expensive course of attempted treatment and a whole lot of regret.
As is typical of the drug company that makes it (Zoetis, formerly Pfizer Animal Health), the published research, generally funded by Zoetis, routinely overstates the benefits and understates the risks. So does the marketing for these drugs.
The company-funded research and product marketing
overstate the benefits and understate the risks
The list of potential adverse effects is long and colourful. At first, the labeled adverse effects were limited to these:
* urinary tract infection
* bacterial skin infection
* dermatitis
* dermal mass (lump in the skin)
* redness (termed 'erythema' on the product leaflet)
* dermal cyst(s)
* pain on injection
* inappropriate urination
* histiocytoma (a type of immune system tumor)
* increased blood urea nitrogen (BUN, an indicator of kidney function)
* lethargy (tiredness, lack of energy)
* vomiting (termed 'emesis' on the product leaflet)
* loss of appetite (termed 'anorexia' on the product leaflet)
* lameness
* cough
Two of the 138 dogs — that's 1 in 69 dogs — treated with Librela in the European clinical trial, conducted to meet licensure requirements, suffered serious adverse effects and were euthanized during or shortly after the study.
One, a 13-year old Bichon Frise, had pre-existing renal insufficiency and heart failure that worsened during the drug trial. The dog was ultimately diagnosed with renal failure and was euthanized 3 days after completing the 12-week study.
The other, an 8-year -old mixed breed dog, developed pancreatitis and was euthanized on Day 74 of the 84-day trial.
. . .
That clinical trial continued for another 6 months with 89 dogs who received monthly injections of Librela. (There was no placebo group in this part of the trial.) Four of the 89 dogs — that's 1 in 22 or 23 dogs — had serious adverse effects.
One dog experienced acute gastroenteritis: abdominal pain, fever, vomiting, and loss of appetite ('anorexia'). This dog recovered with nonspecific veterinary treatment.
One large-breed dog enrolled for stifle OA suddenly developed forelimb lameness attributed to elbow dysplasia.
Two other dogs developed hind limb weakness of unknown cause. One responded to nonsteroidal anti-inflammatory drugs but the other did not.
. . .
In the US, Librela was first approved for use in dogs in May, 2023 and it entered the veterinary market in mid-July of that year. The first adverse event was reported less than 2 months later.
By July of the following year, the FDA recommended a label revision based on 3,637 reports of adverse events in the first 8 1/2 months that Librela was on the market.
NOS = not otherwise specified
Effectively hidden in that long list of concerns is the death of 458 of those 3,637 dogs. That's 1 in every 8 dogs for whom an adverse event report was completed.
In fact, death was the 7th most common 'clinical sign'.
Also note that 'lack of efficacy' was the "adverse event" reported in about 10% of dogs whose people bothered to complete an adverse-event report. This fairly common outcome is greatly under-represented in this initial after-market report.
. . .
The FDA began a Standard Adverse Event Review in April 2024, publishing their report in September, 2024.
They recommended that Zoetis add the following to their product labeling (i.e., the product insert that accompanies the drug).
Post Approval Experience Section (2024)
The following adverse events are based on post-approval adverse drug experience reporting for Librela™. Not all adverse events are reported to FDA/CVM [Center for Veterinary Medicine]. It is not always possible to reliably estimate the adverse event frequency or establish a causal relationship to product exposure using these data.
The following adverse events in dogs are categorized in order of decreasing reporting frequency by body system and in decreasing order of reporting frequency within each body system:
Neurologic: ataxia, seizures, paresis, proprioceptive deficits, paralysis
General: anorexia, lethargy, recumbency
Renal/Urinary: polydipsia, polyuria/pollakiuria, urinary incontinence
Gastrointestinal: vomiting, diarrhea
Musculoskeletal: muscle weakness, muscle tremors, lameness
In some cases, death (including euthanasia) has been reported as an outcome of the adverse events listed above.
In addition, we suggest that owners be advised of the adverse reactions that may occur following administration of Librela™.
While there is concern regarding other signs assessed in this review (Collapse NOS [not otherwise specified], immune-mediated signs, and pancreatitis), the evidence for an association is not as strong as for the signs being included in the PAE [Post Approval Experience] section. Therefore, at this time these signs will continue to be monitored and may be considered for future safety-related labeling updates depending on the evidence in additional cases which may be received.
3. There is no countermeasure or specific treatment ('antidote') for animals experiencing adverse effects
Once it's in, it's in; it's there for the duration (at least 1 month for Solensia and Librela/Beransa, which are given monthly).
You just have to wait it out and hope for the best. Symptomatic treatment is our only recourse.
But as worsening pain or neurologic dysfunction is a fairly common adverse effect, and most vets resort to this drug class because nothing else they've tried was working anymore, whachagunnado?
In a separate article, I'll discuss what to do instead for animals with osteoarthritis pain.
4. Zoetis has already been sued for misleading marketing of Librela
In October 2024, a group of dog owners filed a class-action lawsuit against Zoetis over what they claimed was misleading marketing of Librela.
Specifically, they claimed that Zoetis failed to adequately warn veterinarians and clients about severe adverse events that are associated with Librela, such as neurological injuries, musculoskeletal problems, hepatic and pancreatic damage, and even death.
The primary plaintiff's dog, Jake, received a single dose of Librela in May, 2024, for the management of pain associated with OA of the hip.
Within days, “Jake began experiencing markedly increased thirst, significantly decreased appetite (inappetence), drastically limited mobility (e.g., inability to get up to avoid urinating and defecating on himself), and apparent worsening pain.”
Veterinary treatment was ultimately unsuccessful, and Jake was euthanized because his quality of life was so poor.
Despite two amendments to the original complaint, the suit was dismissed in October 2025. According to the presiding judge, "Consumers failed to adequately plead consumer fraud, product consumer fraud, and warranty claims."
However, "The consumers were granted leave by the court to amend and file a fourth amended complaint, addressing the deficiencies identified in the court's opinion.”
It may have been the first, but I don't think it will be the last lawsuit against Zoetis over this drug class.
. . .
If you are considering or already using this drug class in your dog or cat, please think carefully before proceeding or continuing with it. Consider instead consulting a holistic veterinarian who can talk you through other options. Stay tuned for an article on that topic.
ADDENDUM
After I shared the link to this article with an online group of holistic colleagues, one shared a very interesting perspective.
Hers is a house-call practice that offers in-home euthanasia for pets. She remarked that she sees a couple of "successes" with Librela, where quality of life appears to be extended for a time. But she sees many more cases in which euthanasia is needed because of Librela use.
While these are simply the observations of a working vet, we generally don't see such a lopsided distribution of successes and lethal failures when a new drug class enters the veterinary market.
The problems that led to the decision for euthanasia in her practice range from paralysis (most common) to organ failure to sudden onset of cancer.
Some pets experienced severe adverse effects after just one or two doses, whereas others had been on the drug for some time before euthanasia became the only humane option.
Almost all of the pet owners had no idea that Librela carried the potential for such harms.
The FDA recommended the label revisions I highlighted above in September, 2024. Here we are in January, 2026 and not much appears to have changed in pet owner awareness of the potential for lethal outcomes with these drugs. Hopefully, this article helps to change that.
. . .
ADDENDUM
Two recent experimental studies suggest further concerns for repeated use of anti-NGF therapy:
1. Impaired muscle maintenance and repair.
2. Impaired response to chronic stress, including the development of depression
Fortunately, the second study showed that the adaptogenic herb ashwagandha (Withania somnifera) was helpful in mitigatging the reduction in brain NGF that occurred with chronic stress.
Might ashwagandha be useful in dogs and cats experiencing adverse effects from Librela (Beransa) and Solensia? I don't know yet, but it's not likely to do them any harm.