Antinociceptive effects of sustained-release buprenorphine in a model of incisional pain in rats (Rattus norvegicus)

Abstract

Effective management of postoperative pain is an essential component of the care and welfare of laboratory animals. A sustained-release formulation of buprenorphine (Bup-SR) has recently been introduced to the veterinary market and has been reported to provide analgesia for as long as 72 h. Using evoked mechanical and thermal hypersensitivity tests, we here evaluated the antinociceptive effects of Bup-SR in a model of incisional pain in rats. Paw withdrawal responses were obtained before and 1 through 4 d after surgery. Rats are assigned to receive Bup-SR (0.3, 1.2, or 4.5 mg/kg SC once) or buprenorphine HCl (Bup HCl, 0.05 mg/kg SC twice daily for 3 d). Responses to mechanical and thermal stimuli in the 1.2 and 4.5 Bup-SR groups did not differ from those of rats in the Bup HCl group. Thermal latency on day 3 in rats that received 0.3 mg/kg Bup-SR was significantly different from baseline, indicating that this dose effectively decreased thermal hypersensitivity for at least 48 h. Marked sedation occurred in rats in the 4.5 Bup-SR group. Our findings indicate that Bup-SR at 0.3 or 1.2 mg/kg SC is effective in minimizing hypersensitivity with minimal sedation for at least 48 h (thermal hypersensitivity) and 72 h, respectively, in the incisional pain model in rats.

Figure 1.

Experimental set-up for assessing mechanical hypersensitivity. The rat is placed on wire mesh, and the von Frey device is applied to each hindpaw 10 times.

Figure 2.

Experimental set-up for assessing thermal hypersensitivity. A radiant heat source is applied to the plantar aspect of the rat's hindpaws.

Figure 3.

Weights of rats that received Bup HCl or Bup-SR at various dosages (mg/kg). *, Value is significantly (P < 0.05) different from baseline for group.

Figure 4.

Effects of Bup HCl or Bup-SR at various dosages (mg/kg) on mechanical hypersensitivity (number of foot raises, mean ± SEM) of (A) ipsilateral and (B) contralateral paws. *, Value is significantly (P < 0.05) different from baseline for group; #, value is significantly (P < 0.05) different from that for Bup HCl at the same time point.

Figure 5.

Effects of Bup HCl or Bup-SR at various dosages (mg/kg) on thermal latency (s; mean ± SEM) of (A) ipsilateral and (B) contralateral paws. *, Value is significantly (P < 0.05) different from baseline for group; #, value is significantly (P < 0.05) different from that for Bup HCl at the same time point.