Is it an alternative to morphine?
From time to time the availability of preservative-free morphine for epidural use becomes challenging. In some areas of the world, morphine is not available whereas buprenorphine is. Each of these situations raises the question around whether we can use buprenorphine epidurally, and if so, how does it compare to morphine.
Best practice teaches us that any product used epidurally should be sterile (ie: from a single use vial) and be preservative free, for fear of causing a neurotoxicity (Smith & Yu, 2001).
In our individual situation, morphine was out of production for many months, and of course we wanted to ensure that the dogs and cats under our care were able to be kept pain free during surgery.
If you need to cover the basics of epidural analgesia, you can do so here with Matt’s masterclass which is a great starting point. Ready to bring some debate into your learning? Of course we feel we learn best when we are made to challenge our assumptions. This webinar in our expert series by Dr Fernando Martinez Taboada will do just that. You can watch it here.
The dose we chose to use was taken from Dugdale’s Veterinary Anaesthesia: Principles to Practice which cites 5-15 µg/kg of buprenorphine epidurally. Based on our experience we decided that there was no difference in the analgesic properties compared to our usual choice, morphine. We wrote these cases up and reported in abstract form at the Association of Veterinary Anaesthetists meeting in Lyon, 2016.
Case records (17) from dogs that underwent pelvic limb surgery were reviewed and divided into two groups, receiving morphine (M) 0.1 mg kg—1 or buprenorphine (B) 15 µg kg—1 extradurally, combined with bupivacaine 1 mg kg—1. Injections (0.2 mL kg—1)
Premedication varied between dogs although intramuscular methadone 0.3 mg kg—1 and an NSAID was included in each. Parameters evaluated were end tidal CO2, fractional expired isoflurane (FE’iso), mean arterial pressure and fentanyl requirement intra-operatively with pain score, methadone requirement, and urination recorded post-operatively. Intervention (intravenous methadone 0.3 mg kg—1) was based on Glasgow composite pain scores. Data were analysed for normality using a Kolmogorov-Smirnov test. Parametric data was assessed using t-tests and nonparametric data using Mann—Whitney U test.
There were no significant differences in age, body condition score or body mass between groups. Hypotension (MAP < 60 mmHg) was documented more frequently in group M (5/9) versus group B (0/8). Between groups there were no significant differences in end tidal CO2 (p = 0.56), FE’iso (p = 0.11), fentanyl use (p = 0.38), methadone requirement (p = 0.41), time to first methadone administration (p = 0.59) nor time to first urination (p = 0.92).
Our conclusion was that this higher dose of buprenorphine produced acceptable analgesia without an increase in side effect profile.
With some further reading we discovered a previous study by Smith LJ, & Yu J. (2001) entitled ‘A comparison of epidural buprenorphine with epidural morphine for postoperative analgesia following stifle surgery in dogs’.
This study examined 21 client-owned dogs, using either 4 µg kg—1 buprenorphine or morphine 0.1 mg kg-1. Reasons cited for using buprenorphine in this study were related to cost.
These authors quote several human studies which document an onset of epidural buprenorphine of 20 mins and a duration of action ranging from 6-12 hours.
The main findings from this work were as follows;
Epidural buprenorphine was as effective as epidural morphine following pelvic limb orthopaedic surgery
Fifty percent of dogs in the buprenorphine group and 50% of dogs in the morphine group required rescue analgesic medication
There were no significant differences between groups with respect to any parameters measured
When considering the high requirement for rescue analgesia, we need to remember that the dogs received opioids alone epidurally. It is common practice to include a long acting local anaesthetic alongside opioids (ie: bupivacaine, ropivacaine) and this could have influenced post op pain in the present study, had it been included.
Why epidurally and not systemically?
Work by Inagaki et al (1996) in humans compared the duration of analgesia after either epidural or intravenous buprenorphine using a dose of 4 µg kg−1. Epidural buprenorphine had a slower onset time for analgesia with a longer duration of effect (15–18 hours, versus 7 hours following intravenous administration (same dose). Results of this study suggest that the analgesic effect of epidural buprenorphine is due to local activity within the dorsal horn, and not to systemic absorption.
In conclusion, the main reasons for choosing buprenorphine over morphine relate to cost and availability. Regarding dose, on the basis of the work presented here the range is 4-15 µg kg—1. The unknowns are the benefits of different doses as no dose-finding work has been conducted, and duration of action is yet to be determined.
Gurney M & Miller C. Extradural buprenorphine following methadone premedication in the dog: a retrospective evaluation. Abstracts presented at the Association of Veterinary Anaesthetists Meeting, 20–22nd April, 2016, Lyon, France
Inagaki Y, Mashimo T, Yoshiya I. Mode and site of analgesic action of epidural buprenorphine in humans. Anesth Analg. 1996 Sep;83(3):530-6. doi: 10.1097/00000539-199609000-00016. PMID: 8780276.
Smith LJ, & Yu J. (2001) entitled ‘A comparison of epidural buprenorphine with epidural morphine for postoperative analgesia following stifle surgery in dogs’. Vet Anaes Analg 28 87—96.
This post was written by Matt Gurney.
Matt & Carl established Zero Pain Philosophy to provide educational resources & telemedicine to veterinary professionals enabling optimal management of pain.
Matt Gurney is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and works at Anderson Moores Veterinary Specialists. Matt is Past President of the European College of Veterinary Anaesthesia & Analgesia.
Carl Bradbrook is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and is Past President of the Association of Veterinary Anaesthetists. Carl works at Anderson Moores Veterinary Specialists.
The intended audience for this pain update is veterinary professionals. This pain update is based on clinical experience and independent opinion.