Librela has changed how veterinarians treat arthritis pain in dogs.
Librela, or bedinvetmab, is a monoclonal antibody that blocks nerve growth factor, usually called NGF. NGF plays an important role in pain, especially arthritis pain.
But NGF does more than carry pain signals.
A new paper published in Frontiers in Veterinary Science asks an important question:
Could blocking NGF also affect other parts of the body?
The authors propose that some side effects reported in dogs receiving Librela may be connected by one common mechanism. They call this “neurotrophic withdrawal.”
This is a hypothesis, not proof. But it raises important questions about how anti-NGF drugs work and what we still need to learn about their long-term safety.
What Is Nerve Growth Factor?
The name “nerve growth factor” gives us a clue.
NGF is involved in pain, but that is not its only job. It also helps support certain nerves and helps them function normally.
NGF is involved in several areas of the body, including:
- Pain-sensing nerves
- The nervous system
- Joints and bones
- The bladder and urinary system
- Parts of the brain
Librela works by binding NGF. This reduces the ability of NGF to send pain signals.
For a dog with painful arthritis, that can be helpful.
But the authors of this new paper ask whether reducing NGF activity for long periods could also reduce some of the normal support that NGF provides to nerves and other tissues.
What Does “Neurotrophic Withdrawal” Mean?
“Neurotrophic” sounds complicated, but the basic idea is fairly simple.
Some nerves depend on chemical signals to stay healthy and work normally. NGF is one of those signals.
The authors suggest that repeatedly blocking NGF might create a state where some cells receive less of this normal support.
Think of NGF as doing more than turning on a pain alarm. It may also help maintain some of the wiring behind the alarm.
Turning down the alarm can help with pain.
The question is whether we may also be affecting some of the wiring.
Again, this has not been proven in dogs receiving Librela. The paper presents a biological explanation that researchers can now test.
The “Dual-Hit” Problem in Joints
One of the most interesting ideas in the paper involves bones and joints.
Pain has a purpose. If a joint hurts, a dog usually puts less weight on it.
Blocking NGF can reduce that pain. The dog may then become more active and place more weight on an arthritic joint.
That is the first possible “hit.”
The second involves the role of nerves in bone and joint health.
Research in other species suggests that sensory nerves and NGF-related pathways may help bones respond to increased loads and may play a role in bone repair.
The authors therefore propose a “dual-hit” model.
The dog may place more stress on a damaged joint because it hurts less, while NGF blockade could possibly reduce some of the signals that help the skeleton respond to that increased stress.
This could be important when thinking about reports of rapidly progressive arthritis, fractures, and ligament injuries in some dogs receiving Librela.
But we do not yet know whether this proposed mechanism is actually causing those events.
We Learned Something Similar From Human Medicine
Anti-NGF drugs were also studied for arthritis pain in people.
One of those drugs was tanezumab.
It worked for pain. But some people developed serious joint problems, including rapidly progressive osteoarthritis, or RPOA. Those safety concerns eventually limited the drug’s development.
There was another important finding.
Serious joint problems occurred more often when anti-NGF treatment was combined with NSAIDs than when anti-NGF therapy was used alone. Because of this, limiting long-term NSAID use became part of the safety strategy in the human trials.
That history matters as we study anti-NGF drugs in dogs.
What About Neurologic Problems?
Post-marketing reports in dogs receiving Librela have included signs such as:
- Ataxia, or an unsteady gait
- Weakness
- Changes in behavior or awareness
- Lethargy
- Seizures
Those reports do not prove that Librela caused the problems. Older dogs can develop many of the same signs from unrelated diseases.
The paper raises another interesting possibility.
Some dogs that appear weak or uncoordinated may actually have severe joint instability or pain-related changes in movement. A leg that collapses under weight can sometimes look neurologic.
But the authors make an important point: true neurologic signs should still be treated as neurologic until a proper examination shows otherwise.
The authors also discuss possible ways that long-term changes in NGF could affect the brain. However, this part of the hypothesis is much less certain and needs considerably more research.
What About Urinary Problems?
This is another interesting part of the paper.
NGF helps regulate nerves involved with the bladder and lower urinary tract.
Urinary incontinence has been reported after Librela treatment. The authors propose that reducing NGF signaling could possibly affect the nerves that tell a dog when the bladder is full or help control the bladder and urethra.
Again, this has not been proven.
Urinary incontinence is also common in older dogs and has many causes. A new urinary problem after Librela does not automatically mean Librela caused it.
The authors also stress that increased thirst and urination are different problems from urinary incontinence. Kidney disease, hormonal disease, medications, and other causes still need to be investigated.
What About Lenivia?
This paper is especially interesting because Librela is no longer the only anti-NGF drug developed for dogs.
Lenivia, or izenivetmab, is another anti-NGF monoclonal antibody. It is given at longer intervals.
The authors reviewed information from its clinical trials as well.
In a 9-month study involving 574 dogs, 36.3% of dogs receiving Lenivia met the study’s definition of treatment success at day 90, compared with 21.4% receiving placebo.
Ataxia was reported in 8 of 289 treated dogs and none of the 285 control dogs. Increased thirst and urination were also reported more often in treated dogs. There were other possible explanations for several of the ataxia cases, so this does not prove the drug caused them.
The authors argue that this raises an important question:
Are some safety concerns related to Librela itself, or could some be related to blocking NGF as a whole?
We do not know yet.
What This Paper Does NOT Prove
This point is extremely important.
This was not a clinical trial showing that Librela causes neurologic, urinary, bone, or joint problems through neurotrophic withdrawal.
It is a Perspective article.
The authors took information from basic science, animal research, human anti-NGF studies, regulatory reports, and veterinary safety reports and developed a hypothesis that could explain some of the findings.
They openly acknowledge that there is currently a lack of direct evidence in dogs. Arthritis progression, aging, neurologic disease, and other medical conditions remain possible explanations for many reported problems.
That distinction matters.
A scientifically reasonable hypothesis is not the same thing as a proven cause.
But a good hypothesis tells us what we should study next.
What Should Dog Owners Know?
Librela can provide meaningful pain relief for some dogs with arthritis.
Pain also matters. Leaving severe arthritis pain untreated is not a safe alternative.
But reducing pain is only one part of managing osteoarthritis.
I think dogs receiving anti-NGF therapy should still be monitored carefully. Changes should not automatically be dismissed because a dog is old.
Talk with your veterinarian if you notice new:
- Weakness or difficulty walking
- Loss of coordination
- Sudden worsening of a joint
- Swelling or instability
- Difficulty getting up
- Urinary accidents
- Changes in urination or thirst
- Major changes in activity or behavior
- Seizures or other neurologic signs
The authors recommend documenting a dog’s neurologic and orthopedic status before treatment, slowly returning the dog to activity, reassessing before each dose, and watching for new musculoskeletal, neurologic, and urinary problems.
The Take-Home Message
NGF is not simply an “arthritis pain molecule.”
It is part of a much larger biological system.
Blocking NGF can reduce arthritis pain. But the same molecule is involved in nerve health, bladder function, bone responses, and other normal processes.
This new paper proposes that reducing NGF activity may sometimes have effects beyond pain control.
We do not yet know whether neurotrophic withdrawal explains the adverse events reported in some dogs receiving Librela. We also do not know how often serious adverse events occur or which dogs may be most at risk. The authors specifically point out that the lack of reliable incidence data remains an important gap in our knowledge.
For me, the message is not that dogs with arthritis should be left in pain, it is that pain control should be individualized, multimodal, and monitored carefully.
When we interfere with an important biological pathway, we need to understand not only the benefit we are trying to achieve, but also what else that pathway does.
And with anti-NGF therapy, we still have important questions to answer.
Reference
Federico G, Ilardi A, Elia V, Chieffi S. A neurotrophic withdrawal hypothesis for multisystem adverse events associated with anti-NGF therapy for canine osteoarthritis pain. Frontiers in Veterinary Science. 2026;13:1776920. doi:10.3389/fvets.2026.1776920.
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