In September 2026, the main new cat-arthritis developments are a UK safety update for Solensia and encouraging results from a small controlled stem-cell study. Portela, a longer-acting injectable treatment, also reached Canada and EU markets in July, widening treatment choices there. Feline osteoarthritis is a painful joint disease that can limit a cat's movement and daily activity. The latest evidence changes what owners should monitor and discuss with a veterinarian, but it does not establish one best treatment for every cat.
Table of Contents
- What changed in Solensia's safety information?
- What do the US adverse-event numbers mean?
- How promising is the stem-cell study?
- Where does Portela fit?
- What should owners do now?
What changed in Solensia's safety information?
On september 1, the UK Veterinary Medicines Directorate updated Solensia's product information after pharmacovigilance monitoring. Pharmacovigilance means tracking possible adverse effects after a medicine enters wider use. The revised label says ataxia, increased urination, and increased thirst may occur very rarely.
Ataxia means impaired balance or coordination. "Very rarely" means fewer than one in 10,000 treated animals, including isolated reports, according to the UK Veterinary Medicines Directorate's safety update. Existing packages may not show the change immediately. The regulator says packaging could take up to 12 months to catch up, so owners and veterinarians should consult the current product information rather than relying only on the carton.
What do the US adverse-event numbers mean?
FDA records through June 30, 2026 contained 7,842 spontaneous adverse-event reports associated with Solensia. Of those, 7,626 involved cats, according to the FDA Center for Veterinary Medicine report. Those figures are signals for further safety monitoring, not a count of confirmed reactions caused by Solensia.
A report can follow treatment without proving that the medicine produced the event. The FDA says these reports cannot establish incidence, comparative risk, or causation. The records lack the total number of treated animals and may include illnesses, medications, or clinical circumstances that complicate interpretation. Owners therefore should not convert 7,626 reports into a percentage or use the number alone to compare treatments.
How promising is the stem-cell study?
A randomized, masked, placebo-controlled pilot study published September 4 tested intravenous uterine-derived mesenchymal stromal cells in 35 client-owned cats. Cats receiving the cells had better owner- and veterinarian-assessed outcomes over 90 days than cats receiving saline, according to the study in Frontiers in Veterinary Science. The design makes the finding worth further study, but the trial remains preliminary.
Thirty-five cats and three months of follow-up are not enough to establish long-term effectiveness, identify uncommon risks, or determine how broadly the results apply. Treatment-related events included temporary nausea or vomiting, weakness, lethargy, hypersalivation, and rapid breathing. Researchers also recorded one possible serious hypersensitivity reaction at the higher dose. Owners considering a similar intervention should ask how the proposed protocol, dose, monitoring, and evidence compare with this specific pilot study.
Where does Portela fit?
Zoetis commercially launched Portela, or relfovetmab, in Canada and EU member states in July 2026. This feline anti–nerve growth factor antibody is intended to relieve osteoarthritis pain for up to three months after one under-the-skin injection, compared with monthly Solensia treatment, according to the Zoetis launch announcement. A longer interval may reduce appointment frequency, but it does not make Portela suitable for every cat.
Its availability in Canada and the EU also does not imply availability elsewhere. Portela must not be used in cats younger than 12 months, breeding cats, pregnant or lactating cats, or animals with known hypersensitivity. EU product information also says evidence is unavailable beyond nine months of treatment and in cats with kidney disease above IRIS stage 3.
What should owners do now?
Treatment decisions should weigh the individual cat's response, health conditions, eligibility, and the uncertainty around newer evidence. Useful steps include: Bring a dated symptom log and the names of all current medicines to the appointment so the veterinarian can assess timing and possible clinical confounders.
- Ask the clinic to check the current Solensia information, especially if the package does not mention the September update.
- Record when an injection was given and when any new balance, drinking, or urination changes appeared.
- Contact the treating veterinarian about new unsteadiness or noticeable changes in thirst or urination rather than assuming the medicine caused them.
- If Portela is available locally, confirm age, reproductive status, hypersensitivity history, kidney status, and the planned duration of treatment.
- When considering stem-cell treatment, ask whether the evidence extends beyond the small 35-cat, 90-day pilot.