Monoclonal Antibodies Therapeutics - a Breakthrough in Pet Health

What Are Monoclonal Antibodies?

These are medications designed to mimic the body’s natural immune response. Antibodies are proteins produced by the immune sy2025 Breakthroughs in Pet Health – Monoclonal Antibodies

Welcome 2026! As 2025 wrapped up, I asked our veterinary team this question: “If you had to pick ONE, which new technology, protocol, research study or equipment made the biggest impact this year in animal medicine?” Two words always come up and it’s not Artificial Intelligence (OK that came up too, but we can do that one next month!): Monoclonal Antibodies (mAb). These therapeutics have been around for decades on the human side – Humira, Keytruda, Herceptin to name a few; and newer ones like Skyrizi and Tremfya. These therapies have created a new class of therapeutics that modulate the immune system and changed how we treat cancer, autoimmune diseases, many inflammatory conditions and some viral diseases that were typically very challenging and sometimes dangerous with traditional therapies, due to side effects.

In cats and dogs, several new mAb therapies have been approved or conditionally approved by the FDA. But do they work? Are they safe? Are they affordable? I’m usually a skeptic for at least a year after a new med is released. We’ll discuss some of the most popular and controversial ones, but first let’s dive into what mAb therapy is and how they work.

Cytopoint (Lokivetmab)

This is a once-a-month injection that has been a game changer for pet owners with pets suffering from seasonal allergies. Atopic dermatitis (Atopy) is a lifelong disease of the immune system triggered by environmental allergens that cause chronic itching and bacterial skin infections. There is no cure, and treatment is lifelong. The disease causes a cascade of events with proteins called cytokines involved in communicating with the nervous system and resulting in itchy skin and inflammation. This mAb was created to target one of the main cytokines involved in this cascade called interleukin-31 (IL-31). Cytopoint was one of the first FDA-approved mAbs for use in dogs. Unfortunately, it is currently not effective in cats because the IL-31 cytokine is specific to dogs. Cytopoint works like the pill, Apoquel, and is priced pretty close, but Apoquel needs to be given once or twice a day to be effective. Injections may be more expensive in larger pets and more cost-effective for smaller dogs, but in some dogs, it works better than pills. Reactions are pretty uncommon, but include pain at the injection site, lethargy, fever, and sometimes gastrointestinal (GI) issues. These issues have been seldomly seen in our patients. Some studies have even shown that the response improves month after month when it’s continued – meaning less scratching and chewing at feet and more comfortable pets.

Canine Parvovirus mAb (CPMA)

Parvo (CPV) in dogs is highly contagious and potentially lethal in many, mostly unvaccinated young dogs, killing up to 91% of dogs that are not treated. Many dogs succumb to the disease, which affects the gut and bone marrow resulting in a weakened immune system and severe vomiting and diarrhea. Many dogs succumb to the disease after days-to-weeks in the hospital. This mAb is the first FDA conditionally-approved treatment for CPV infection. A single injection of this mAb targets the virus directly and neutralizes it before it can enter cells of the GI lining. This mAb has changed the outcome of many dogs infected with this virus. Unfortunately, it’s a pretty expensive treatment (several hundred per vial) – but may be worth the less days of treatment and days in the hospital.

Gilvetmab

This is a newer mAb from Merck Pharmaceuticals and does not yet have a trade name. It targets some of the most common, malignant skin tumors seen in dogs – mast cell tumors and melanomas. The cancers can be very aggressive, and often treated with a combination of surgery, radiation and chemotherapy treatments. These tumors grow by suppressing immune cells and evading the body’s checkpoint system. This prevents the immune system from removing these cells and causing cancerous tumors to survive and flourish. Specific antibodies have been designed to “repair” the checkpoint system, improve the immune system and target these cancerous cells. Currently this medication is only available to veterinary oncologists. Side effects are reported to be low, especially in comparison to traditional treatment, but unfortunately a full course can cost in the tens of thousands for a full 10-week treatment.

Solensia (Frunevetmab) & Librela (Bedinvetmab

These monoclonal antibodies are among the most widely used—and most controversial—therapies in veterinary medicine today, largely because of their use in older, and usually sicker, pets. Osteoarthritis is one of the most common chronic conditions affecting animals. Approximately one in four dogs of all ages, and the majority of senior dogs, are affected, with joint disease often developing years before visible pain. In cats, osteoarthritis is even more prevalent but vastly underrecognized—over 60% of cats older than six and more than 90% of cats over twelve show evidence of degenerative joint disease. Because cats rarely limp and instead display subtle behavioral changes, arthritis pain frequently goes untreated for years.

Traditional treatment in dogs has relied on daily non-steroidal anti-inflammatory drugs (NSAIDs), which block COX enzymes involved in inflammation. While effective, long-term use can carry risks, including gastrointestinal irritation and potential kidney or liver toxicity. In cats, treatment options are far more limited, as chronic NSAID use is generally unsafe.

Nerve growth factor (NGF) is produced in arthritic joints and plays a key role in transmitting pain signals to the nervous system. Solensia (for cats) and Librela (for dogs) were specifically designed to neutralize NGF, reducing the perception of pain without altering the underlying joint disease. As a result, pets may feel well enough to be more active despite ongoing arthritis, muscle loss, or joint instability—raising concern that increased activity could predispose some animals to injury. These injections are much more affordable in comparison to other mAbs, often $100-$200 each.

Although these drugs are FDA-approved and underwent rigorous safety testing, their rapid adoption led many veterinarians to field concerns about worsening mobility or neurologic signs within the first year of use. The FDA even released a notice to veterinarians about the increased reports of adverse events including neurologic symptoms associated with this therapy (https://www.fda.gov/animal-veterinary/product-safety-information/dear-veterinarian-letter-notifying-veterinarians-about-adverse-events-reported-dogs-treated-librela). As a result, some clinicians reserve these medications for cases where other options have been exhausted, raising the question of whether earlier use in younger, healthier patients might yield more consistent outcomes. Reported side effects are often mild, including injection-site discomfort, increased drinking and urination, and gastrointestinal upset. At the same time, many pet owners report significant improvements in comfort and quality of life, choosing to continue monthly injections.

All things considered, 2025 was a pretty great year for breakthroughs in veterinary medicine, but as with every innovation, vigorous debate helps to clarify their role in treating sick pets. It looks like mAbs are here to stay as there are plans for a cat allergy injection similar to Cytopoint in the works, as well as additional anti-cancer products. There is also a potential plan for longer-acting anti-NGFs that would extend the half-life on products used for arthritis to up to 3 months per injection. Happy New Year!

For more information about these therapies, or any concerns about your pet, contact our office: City by the Sea Vet, 848-217-5000 or visit our website www.citybytheseavet.com