Influence of buprenorphine analgesia on post-operative recovery in two strains of rats

The objective of this study was to establish an effective post-operative an algesic regimen tor Spraguc-Dawley (SD) and Dark Agouti (DA) rats. Buprenor phine (0.01 or 0.05 mg/kg), a partial mu opioid agonist, was administered s ubcutaneously immediately on completion of a standardized surgical procedur e, involving anaesthesia, laparotomy and visceral manipulation. Two of tile four treatment groups and the saline control group received a second injec tion 9h later. Behavioural observations by three independent observers prov ided no information in assessing pain in this model. All rats lost weight, consumed less food and water after surgery. On the first day, both SD and D A rats receiving buprenorphine lost less weight than untreated control grou ps. Using weight loss as an efficacy criterion, low-dose buprenorphine, giv en once or twice, provided effective analgesia in SD rats. A higher single dose provided no additional benefit and a second dose was detrimental, redu cing body weight and food intake. In DR rats, the high dose, given twice, a ppeared to be more effective than the lower dose. All DA cage cohorts consu med < 10% pre-operative food despite buprenorphine treatment, suggesting a higher dosage may be necessary. However, all SD and 80% DA rats who receive d no buprenorphine gained body weight on the second day, whereas most of th e buprenorphine-treated rats continued to lose weight for another 2 days, d espite increased food consumption by both strains. Buprenorphine may advers ely affect intestinal function over a number of days due to its enterohepat ic circulation; this effect may be more severe in DA rats. Adverse metaboli c effects of buprenorphine and other opioids may preclude their use in the future if it can be shown that non-steroidal anti-inflammatory drugs (NSAID s) provide equally effective analgesia.