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No leeway for the spay: A comparison between methadone and buprenorphine for perioperative analgesia in dogs undergoing ovariohysterectomy.

In this paper summary we  compare post-operative analgesia following premedication with methadone or buprenorphine.

Shah, M.D., Yates, D., Hunt, J. and Murrell, J.C. (2018). A comparison between methadone and buprenorphine for perioperative analgesia in dogs undergoing ovariohysterectomy. Journal of Small Animal Practice

WHAT DID THE RESEARCH FIND? 

At the clinically relevant doses used, methadone produced superior postoperative analgesia compared to buprenorphine in dogs undergoing ovariohysterectomy. 

HOW WAS IT CONDUCTED? 

Eighty female dogs were recruited to an assessor-blinded clinical trial. Dogs were randomly allocated into four groups of 20 and each group administered an intramuscular premedicant combination as follows: 

  1. Methadone (0.3mg/kg) and acepromazine (0.05mg/kg) = 20 dogs
  2. Methadone (0.3mg/kg) and medetomidine (0.01mg/kg) = 20 dogs
  3. Buprenorphine (0.02mg/kg) and acepromazine (0.05mg/kg) = 20 dogs
  4. Buprenorphine (0.02mg/kg) and medetomidine (0.01mg/kg) = 20 dogs 

Anaesthesia was later induced with intravenous propofol and maintained with isoflurane gas. 

Pain scoring, among other variables, was performed before premedication, 30 minutes later and then every hour for 8 hours and was performed in each case by the same assessor who was blinded to treatment group. The following two pain scoring systems were used:

  1. The validated short form of the Glasgow Composite Pain Scale (SF-GCPS),
  2. A dynamic interactive visual analogue scale (DIVASpain). 

The SF-GCPS, having been validated for the assessment of pain in dogs in a clinical setting, was the primary measure of pain in this study. However, two pain scoring scales were utilised to increase the reliability of results and to allow comparison with other studies that used similar pain assessment protocols. 

A second dose of the allocated test opioid was scheduled for administration 5 hours post premedication in all dogs. However, if indicated beforehand (i.e. a SF-GCPS score of ≥5/20 in non-ambulatory dogs or ≥6/24 in ambulatory dogs) rescue analgesia was provided with intramuscular methadone at 0.3mg/mg at any time point. 

0.2mg/kg meloxicam was administered subcutaneously to all dogs after their last assessment (i.e. 8 hours postoperatively) as additional analgesia. 

RESULTS

Rescue analgesia was required by significantly more dogs premedicated with buprenorphine (18/40 dogs) compared to that of methadone (8/40) (P-value=0.017). Of these cases, 16/40 in the buprenorphine and 6/40 in the methadone group required additional analgesia before the scheduled 5 hours post premedication. 

Overall, SF-GCPS and DIVASpain scores were significantly lower in methadone groups compared to the buprenorphine groups. 

The choice of sedative, or the interaction between sedative and opioid had no effect on SF-GCPS or DIVASpain scores. 

WHY IS IT IMPORTANT? 

Ovariohysterectomy is one of the most frequently performed procedures in veterinary practice. It has been shown to have the potential to cause moderate to severe acute postoperative pain in dogs and the provision of perioperative analgesia is essential for patient welfare.  

Methadone and buprenorphine are reported to be the two most widely used opioids in the UK for surgical pain (Hunt et al. 2015). Recent studies investigating buprenorphine have shown that it provides adequate analgesia for ovariohysterectomy in dogs. However, there have been limited studies directly comparing buprenorphine and methadone with respect to analgesia. 

In 2013 the proportion of practices stocking methadone in the UK was 57.3% compared to 98.9% carrying buprenorphine (Hunt et al. 2015). Methadone dose unfamiliarity, drug safety and the potential for adverse events are suggested as possible explanations for this discrepancy. The dose of methadone used in this study (3mg/kg) is lower than the 0.5-1mg/kg range given in the Summary of Product Characteristics (SPC). However, this is a dose that is widely accepted to provide good analgesia whilst avoiding some of the dose-dependent adverse effects such as vomiting and cardiorespiratory depression which may be seen at higher doses (Credie et al. 2010). 

In conclusion, the study supports the hypothesis that methadone provides superior postoperative analgesia to buprenorphine in dogs undergoing ovariohysterectomy. By demonstrating that the lower dose of 0.3mg/kg provides efficacious analgesia without adverse effect, the authors hope to dispel concerns regarding methadone administration.

Link to the full paper: https://onlinelibrary.wiley.com/doi/abs/10.1111/jsap.12859

Article by
Dr. Dan Cripwell
BSc (Hons) BVSc CertAVP (EM) PgCert (VPS) MRCVS

Veterinary Technical Advisor UK
RCVS Recognised Advanced Veterinary Practitioner

Originally published: Thursday, 13th September 2018
Last updated: Wednesday, 7th November 2018

References

Credie, R.G., Neto, F.J.T., Ferreira, T.H., Aguiar, A.J., Restitutti, F.C. and Corrente, J.E. (2010). Effects of methadone on the minimum alveolar concentration of isoflurane in dogs. Veterinary anaesthesia and analgesia. 37(3): 240-249. 

Hunt, J.R., Knowles, T.G., Lascelles, B.D.X. and Murrell, J.C. (2015). Prescription of perioperative analgesics by UK small animal veterinary surgeons in 2013. The Veterinary Record. 176(19): 493

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