Research and analysis

Results of in-depth assessment of selected adverse events for Librela Solution for Injection for Dogs

Published 16 February 2026

As part of our surveillance activities, we have completed an in-depth assessment of the following adverse event reports:

• Death
• Arthritis (specifically in relation to faster than expected progression of arthritis)
• Human exposure reports

Events reported to Marketing Authorisation Holders (MAHs) and the VMD are coded using the globally standardised dictionary for Veterinary Dictionary for Drug Regulatory Affairs Activities (VeDDRA) which can be found at VeDDRA.

1. Conclusion of current surveillance results

The VMD is confident that the overall benefit-risk balance of the product remains positive based on the data available at this time. Many dogs experience significant improvement of their symptoms following Librela administration.   

Additional adverse events are currently undergoing assessment.

We strongly encourage veterinary professionals to ensure they are following the recommendation of the Summary of Product Characteristics (SPC) and, alongside dog owners, reporting related adverse events.

Further information regarding how to submit a high-quality adverse event report can be found at how to report adverse events

The adverse event frequency data below has been calculated following the VMD’s new method of calculation.

2. Death

Inevitably, some adverse event cases have a fatal outcome (inclusive of euthanasia). As this product is used for the treatment of osteoarthritis, Librela is primarily used in an older population of dogs. Many of these dogs have, or are more likely to have due to their age, diagnosed or undiagnosed pre-existing or concurrent medical conditions and many are being administered multiple medications.  

Using data available since authorisation, the frequency of death following administration of Librela is rare, occurring in 1 to 10 per animals per 10,000 estimated animals treated.

In many cases, there is limited data provided or minimal / no investigation into the cause of death. The VMD assessment found that there does appear to be a small subset of dogs 6+ years of age who rapidly deteriorate within 14 days of Librela administration. However, there is currently no clear pattern in terms of symptoms or the number of doses received. For example, some of the dogs have received Librela for years prior to these events occurring. Many of these dogs experienced neurological signs, but the neurological signs had an inconsistent presentation. It is therefore unclear whether this deterioration is product related.

Overall, there is no clear pattern in terms of symptoms or the number of doses received, so it is currently unclear whether many of these reports are product related.  

3. Arthritis

We have identified a small subset of dogs where arthritis or similar adverse events have been reported following administration of Librela, and in which pre-existing osteoarthritis was suspected to be or appeared to be progressing faster than would be expected in an average dog. These reports equate to a very rare frequency, occurring in less than 1 animal per 10,000 estimated animals treated.

Rapidly Progressive Osteoarthritis (RPOA) in people is widely defined as rapid joint destruction characterised by significant radiographic joint space narrowing or subchondral bone collapse in a short period of time (6 months to 1 year). There is no definition in veterinary medicine and many adverse event cases do not provide this level of detail. From those cases where imaging descriptions were provided, there do appear to be some emerging patterns which do not fully align with how RPOA presents in people. There are often relatively few, or no osteophytes seen in RPOA, whereas these were a feature in many of the suspected RPOA-type event cases in dogs. Mineralisation of soft tissues, periosteal reaction and bone lysis / erosion were often reported, all signs that may be, but are not always seen in people with RPOA. Joint effusion and synovitis were also often described in reports, which are commonly seen in RPOA but also many other joint conditions. This complicates further the determination of whether an RPOA-type syndrome or another atypical syndrome is occurring in dogs and, if so, how it would be defined for future monitoring.

Identifying whether there is a causal link to Librela administration is complicated by a range of factors, including:

• the naturally wide range of rates of progression of osteoarthritis in individual animals, even when no medications are administered
• the lack of serial imaging which makes progression difficult to evidence
• pre-existing severe osteoarthritis which would be expected to worsen to some extent over time
• the co-administration of one or more products
• dogs with known risk factors such as being overweight or inappropriately exercised
• off-label use; defined as use of a medicine outside of the recommendations of the SPC, such as overdosing or use for reasons other than those recommended in the SPC.

Many of the dogs were concurrently administered non-steroidal anti-inflammatory drugs, with some dogs additionally administered other pain-relieving medications. Again, more evidence is required to determine whether a product interaction could be a risk factor in the development of any faster than expected osteoarthritis progression.

To gather more evidence, Zoetis is carrying out multiple studies and has future work planned. The VMD is aware of these activities. Zoetis is also utilising expert knowledge to assess adverse events received. The VMD will continue to review additional data received from all sources and, if there is enough evidence, additions will be made to the SPC.

4. Human exposure

Using data available since authorisation, the frequency of human exposure following administration of Librela from authorisation is very rare, meaning there is less than 1 report of human exposure per 10,000 estimated animals treated.  

80% of these cases involved injection site injuries (needlestick injuries) such as bleeding, pain, swelling or redness, and 12.5% involved eye irritation. 95% of cases involved veterinary professionals administering the medication, or involved veterinary professionals being exposed to the medication. No long-lasting events were reported. We remind veterinary professionals, especially those who are pregnant, trying to conceive and breastfeeding to take extreme care to avoid accidental self-injection and in the case of accidental self-injection, to seek medical advice immediately, showing the package leaflet or the label to the physician.

5. Lack of efficacy

Using data available since authorisation, the frequency of lack of efficacy following administration of Librela from authorisation is rare, occurring in 1 to 10 animals per 10,000 estimated animals treated. This calculation has been done following the VMD’s new processes as described in Calculation of adverse event incidence.

Focusing on data received between August 2024 and July 2025, in just over half of the reports of lack of efficacy additional products were being administered. In many cases, multiple pain relief / anti-inflammatory medications were administered, suggesting more severe and possibly intractable disease.

Only 5% of reports indicated lack of efficacy from the initial dose; most dogs had been administered multiple Librela doses prior to the reduced / lack of efficacy being identified.

Many reports did not provide enough detail to determine the exact reasoning for perceived lack of efficacy, and in some reports the symptoms identified as exhibiting lack of efficacy did not correlate with the intended indication of the product (to alleviate pain).

A quarter of reports described the product’s effects as ‘wearing off’ early. In over half of these, this occurred around 3 weeks post-administration and in 16% of cases, this occurred less than 2.5 weeks after administration.

It is unclear whether any of the reports of lack of efficacy are related to anti-drug antibodies, as referenced in section 4.4 of the SPC: ‘This veterinary medicinal product may induce transient or persistent anti-drug antibodies. The induction of such antibodies is uncommon and may have no effect or may result in a decrease in efficacy in animals that responded to treatment previously’, as anti-drug antibodies are not routinely tested in a clinical setting. Field studies showed that the appearance of anti-bedinvetmab antibodies was infrequent.

We have agreed with Zoetis’ proposal to closely monitor further reports. We will be working with them to ensure that the data collected is as comprehensive as possible and to determine if further studies could provide additional information, to ensure that the SPC adequately reflects the evidence.

6. Additional events

Data received between August 2024, and July 2025 was analysed for the events recumbency, muscle weakness, tremor and lameness. In some of these reports, the cause of these signs is already more adequately described on the SPC. For example, muscle weakness was reported alongside other signs that would in combination be more specifically described as ataxia. Other terms have been evaluated through assessment of associated terms, for example, lameness reported alongside progression of arthritis.

In some of the cases, these signs presented as secondary to other disease processes such as neoplasia. There were no clear patterns identified.

For all these events, we have determined that there is not currently adequate information to determine a causal relationship with Librela or addition to the SPC. We have agreed with Zoetis’ proposal to closely monitor further reports.

7. Reporting frequency

Based on complete UK data that has been received across all strengths of Librela Solution for Injection for Dogs since authorisation, the frequency of adverse events in animals is uncommon, occurring in 1 to 10 animals per 1,000 estimated animals treated.

This includes reports where more than one product was used, reports when the product was used off label, that is using a medicine in a way that is not specified on the product’s label, or reports where, on further evaluation, there were other reasons for the adverse reaction occurring.

We will continue to review data as it is received, and further data-led actions will be taken if appropriate.