What’s new in pain management and analgesic research?

2 September 2024

To mark Pain Awareness Month, we’re looking at some new research in pain management and analgesics in small animal veterinary medicine.

1) Comparison of analgesic efficacy of tramadol, morphine and methadone in cats undergoing ovariohysterectomy. Goich et al. Journal of Feline Medicine and Surgery.

This study compared the intra- and postoperative analgesic efficacy of methadone, morphine and tramadol in 30 client-owned healthy female cats undergoing ovariohysterectomy.

Cats were randomly assigned to receive one of the following premedication treatments intramuscularly: methadone (0.2 mg/kg; n = 10); morphine (0.2 mg/kg; n = 10); or tramadol (3 mg/kg; n = 10). Intraoperative analgesia was evaluated using requirements of rescue analgesia and isoflurane during surgery, and postoperative analgesia was assessed using the UNESP-Botucatu Multidimensional Composite Pain Scale.

Intraoperative rescue analgesia was required in 77% of cats and postoperative rescue analgesia was required in 27% of cats up to 6 hours after extubation. There were no significant differences between groups in intra- and postoperative rescue analgesia, pain scale scores and end-tidal isoflurane concentrations. Post-anaesthetic hyperthermia occurred with all opioids and was more frequent in the tramadol group, hence body temperature should be monitored closely during recovery. The frequency of cats requiring postoperative rescue analgesia should be considered in clinical practice decision making.

2) Comparison of grapiprant and meloxicam for management of postoperative joint pain in dogs: A randomized, double-blinded, prospective clinical trial. Cassemiche et al. Journal of Veterinary Internal Medicine.

This randomized, double blinded, prospective clinical trial investigated the analgesic benefit of grapiprant versus conventional NSAID (meloxicam) for the management of postoperative joint pain in dogs.

Forty-eight dogs presented with cranial cruciate ligament disease and treated by tibial plateau leveling osteotomy (TPLO) received a subcutaneous injection of 0.2 mg/kg of meloxicam and were randomly assigned to receive either oral grapiprant (2 mg/kg) or meloxicam (0.1 mg/kg), once a day for 14 days.

Grapiprant and meloxicam were both associated with decreasing postoperative pain after TPLO. Three days after surgery, grapiprant-treated dogs had lower pain interference scores compared to meloxicam-treated dogs at day 3 and day 10, and lower pain severity scores at day 3. A better overall quality of life as assessed by the owner and a significant improvement of the orthopedic recovery assessed by a veterinarian after 15 days was demonstrated with grapiprant. These findings support the use of grapiprant as an alternative analgesic to meloxicam for management of postoperative joint pain.

3) Owner survey suggests cats may be undertreated for pain compared to dogs after an elective ovariohysterectomy or orchiectomy. Adams et al. American Journal of Veterinary Research.

Differences in pain management between dogs and cats after surgical sterilization were assessed using an online survey to 175 clients owning 92 dogs and 83 cats from a high-volume, low-cost veterinary clinic in Michigan.

Owners were asked if their pet was discharged with analgesics, if they were administered as prescribed, and if their pet was painful at home. Analgesics were prescribed significantly less frequently to cats (6.7%) after surgical sterilization compared to dogs (16%), a more than 50% difference between the two species, supporting previous studies that have reported that cats are sometimes not adequately treated for pain. Owners reported that 28% of dogs and 17% of cats appeared painful at home.

As cats were prescribed analgesics less often than dogs, this suggests that pain in cats may not be well appreciated by pet owners and veterinary professionals, and therefore may not be always appropriately managed.

4) Development and validation of a pain scale in guinea pigs. Benedetti et al. Journal of Exotic Pet Medicine.

This new study aimed to develop and validate the first pain assessment scale for guinea pigs to be used in clinics by veterinarians. The scale was designed using pre-existing pain scales from other species and was based on knowledge of signs expressed by guinea pigs in pain.

Selected animals were 58 healthy guinea pigs presented for health checks or elective surgeries such as neutering, and guinea pigs presented with painful conditions such as dental diseases, urinary tract diseases, gastric dilation, otitis, or ovarian cysts. Pain scores were attributed from videos filmed during the animal’s consultation and an information sheet completed with details on appetite, fecal production, and behavior at home.

Whilst the specificity was 87.5%, the sensitivity of the pain scale was 52% and not good at detecting pain when a guinea pig was actually painful. However, it was good at excluding pain in non-painful animals. This is the first step towards a standardized assessment of pain in guinea pigs, however, it should not yet be used in a clinical context and further work is needed to obtain a useable scale.

BSAVA resources on pain management and analgesia

BSAVA Guide to Pain Management in Small Animal Practice https://www.bsavalibrary.com/content/book/10.22233/9781910443453

BSAVA library collection on pain management https://www.bsavalibrary.com/content/pain-management

BSAVA Manual of Canine and Feline Anaesthesia and Analgesia https://www.bsavalibrary.com/content/book/10.22233/9781910443231