Fentanyl and methadone used as adjuncts to bupivacaine for lumbosacral epidural analgesia in sheep

Abstract

Six healthy, female, mixed-breed 18-24-month-old sheep weighing 30-48 kg were submitted to lumbosacral epidural bupivacaine in combination with either methadone or fentanyl. Epidural catheters were placed in six sheep that were given three treatments: (Bup) bupivacaine (0.5 mg/kg) alone; (BupMet) bupivacaine (0.25 mg/kg) plus methadone (0.3 mg/kg); and (BupFent) bupivacaine (0.25 mg/kg) plus fentanyl (0.002 mg/kg). Haemodynamic variables, respiratory rate, rectal temperature, analgesia by applying a standard painful stimulus, motor block and sedative scores were compared among the three treatments. These parameters were determined before epidural administration and at 5, 10, 20, 30, 60, 90, 120 minutes after treatment administration, and then every 60 minutes thereafter until the end of analgesic effect. Parametrical data were analysed by proc glimmix (SAS) for repeated measures on time and means tested by ls-means. Non-parametrical data were analysed by Fisher's exact test. Duration of analgesia was longer with BupMet (240 minutes) compared with BupFent (180 minutes; P=0.0127), but BupMet was similar to Bup (240 minutes). Both treatments with opioids produced moderate motor blockade. BupMet and BupFent produced mild sedation. Only treatment with bupivacaine alone induced cardiovascular and respiratory rate changes that stayed within acceptable limits.

Use and Efficacy of Analgesic Agents in Sheep (Ovis aries) Used in Biomedical Research

“…12 However, the addition of methadone to bupivacaine did not extend the analgesic effect. 13 Ketamine-bupivacaine, using a lower dose of bupivacaine compared to that used as a sole agent, resulted in a comparable state of analgesia to bupivacaine alone. 10 Lidocaine was used in 11 of the 29 papers reviewed.…”

“…45,67 These studies recorded time to voluntary leg withdrawal from the stimulus. Other studies utilized superficial or deep muscle pinpric ks, 3,[11][12][13][14]17,21,22,26,39,42,59 as an alternative method of mechanical stimulation of so-called 'first-pain.' 9 This method tends to evaluate analgesia by using a scale based on reaction to the stimulus.…”

“…2 Methadone was included in 2 studies. 11,13 In one study, when administered alone, epidural methadone produced moderate length analgesia and mild to moderate motor blockade, with minimal effect on physiologic parameters. 11 Combination with bupivacaine produced a reduced duration of analgesia.…”

“…In a later study by the same authors using the bupivacaine-methadone combination, moderate motor blockade was produced, but mild sedation was reported, likely as a result of the opioid component. 13 Morphine, a full μ agonist, was administered epidurally to induce analgesia in one study. 12 Only mild analgesia resulted.…”

Pain relief in sheep

“…AS pleased as I am to see research improving the weight of evidence behind pain relief in sheep (DeRossi and others 2016), I feel it is important to note that as bupivacaine, fentanyl and methadone are not contained in the table of allowed substances in Commission Regulation EU No 37/2010 they cannot be prescribed under the cascade to food‐producing animals in the UK/EU.…”