A single Solensia injection lasts about one month. The medication is designed to be given every 28 days as an ongoing monthly treatment for cats with osteoarthritis pain. Most cats reach peak drug levels in their bloodstream within three to seven days after the injection, and the pain-relieving effects carry through until the next dose.
How the Monthly Cycle Works
Solensia (frunevetmab) is a monoclonal antibody, which means it’s a lab-made protein that targets a specific pain signal in your cat’s body. Unlike a pill that gets processed in hours, this type of drug breaks down slowly. The elimination half-life is approximately 10 days, meaning the drug concentration drops by half roughly every 10 days after peaking. By the time a month has passed, levels have dropped enough that a new injection is needed to maintain consistent pain control.
The injection is given under the skin by your veterinarian. Cats weighing 5.5 to 15.4 pounds get one vial (1 mL), while cats weighing 15.5 to 30.8 pounds get two vials (2 mL). The target dose is based on body weight, so the vet doesn’t need to do any complicated calculations beyond checking which weight range your cat falls into.
When You’ll See Results
Don’t expect overnight changes. One clinical study found that cat owners noticed improved mobility in as little as 14 days after the first injection. Some cats respond faster, while others take longer to show visible improvement. The drug also builds in your cat’s system over time. Steady-state levels, where the amount of drug in the body stabilizes at a consistent therapeutic level, are typically reached after two monthly doses. This means the second and third months of treatment often produce more noticeable results than the first.
If your cat doesn’t seem to improve much after the first injection, it’s worth continuing through at least two or three doses before deciding whether it’s working.
How Long Cats Stay on Solensia
Because osteoarthritis is a chronic condition, Solensia is intended as an ongoing monthly treatment rather than a short course. There’s no set end date. As long as the medication is helping and your cat tolerates it well, the monthly injections continue indefinitely.
That said, the clinical data supporting its safety and effectiveness currently extends to about three months of use. Short-term studies, including in cats with early kidney disease, show the drug is well tolerated over that period. Longer-duration safety data beyond three months is more limited, which is worth discussing with your vet if your cat has been on the medication for an extended stretch. Your vet can monitor for any changes over time.
Can It Stop Working?
One thing to be aware of with any monoclonal antibody treatment is that the body can develop antibodies against the drug itself. Because Solensia is a protein-based therapy, some cats may eventually produce anti-drug antibodies that interfere with its effectiveness. If your cat initially responded well but the pain relief seems to fade after several months of treatment, this immune response could be a factor. There’s no simple test for this in routine practice, but a noticeable decline in benefit is worth bringing up with your veterinarian.
What Happens if You Miss a Dose
Since the drug’s half-life is about 10 days, levels drop meaningfully in the weeks after an injection. If you go significantly past the 28-day mark, your cat’s pain relief will taper off. Missing one dose won’t cause a dangerous withdrawal or rebound effect, but your cat will likely become less comfortable as the drug clears from their system. When you resume treatment, it may take another injection or two to get back to the steady-state levels that provided the best relief.
Keeping appointments on a regular monthly schedule gives the most consistent results. Some veterinary clinics offer reminder systems to help you stay on track.