The influence of pre-anaesthetic administration of buprenorphine on the anaesthetic effects of ketamine/medetomidine and pentobarbitone in rats and the consequences of repeated anaesthesia

Rats received pentobarbitone (60, 48 and 36 mg/kg i.p.) or ketamine/medetom idine (75/100, 60/80 and 45/60 mg/mu g/kg i.p.) alone, or one hour followin g buprenorphine (0.5 mg/kg s.c.). Animals were anaesthetized once per week for 6 weeks with one of three anaesthetic doses according to a randomized b lock design. In the pentobarbitone group, animals which received buprenorph ine had longer sleep times (236 +/- 22 cf. 204 +/- 21 min) and longer durat ions of surgical anaesthesia (83 +/- 14 cf. 27 +/- 8 min) (P<0.01), these e ffects being potentiated with increasing anaesthetic doses (P<0.01). A grea ter degree of respiratory depression was found in animals that received bup renorphine (P<0.01) although this was judged clinically acceptable in all c ases. Unexpectedly high mortality and a high incidence of anaesthetic compl ications (nine of 16 animals) in the ketamine/medetomidine group made stati stical analysis of these data impossible. We conclude that for pentobarbito ne, preanaesthetic administration of buprenorphine reduces the dose of anae sthetic required to produce surgical anaesthesia, in addition to the presum ed benefits of pre-emptive analgesia. In view of the high mortality encount ered, we advise caution when considering preanaesthetic use of opioids in c ombination with ketamine/medetomidine in rats.