Analgesic effect and pharmacological mechanism of fentanyl and butorphanol in a rat model of incisional pain

Objectives: To explore analgesic effects of fentanyl and butorphanol on incisional pain in rats and to investigate the pharmacological mechanism of combination. Methods: Seventy rats were randomly divided into control group (group N, n = 10), fentanyl group (group F, n = 30), and butorphanol group (group B, n = 30), to determine median effective dose (ED50) in fentanyl and butorphanol. Another 50 rats were treated with both fentanyl and butorphanol (joint group) to quantitatively detect response rate of joint application. Ninety rats were randomly divided into 1/4 ED50 fentanyl (group 1, n = 30), 1/2 ED50 fentanyl (group 2, n = 30), and 3/4 ED50 fentanyl (group 3, n = 30), to detect the correlation between combined pharmacological effects of 2 drugs and their dose proportionality. Statistical analysis was performed using SPSS 17.0. Results: Probit analysis revealed that ED50 of fentanyl was 4.1 mu g/kg, whereas ED50 of butorphanol was 295 mu g/kg. The qualitative response rate of combination (P-o) was 0.84, and expected qualitative response rate (P-e) was 0.75, with no statistical significance (P = 0.3). Furthermore, probit analysis showed that 155 mu g/kg butorphanol with 1/4 ED50 fentanyl could reach experimental ED50 of combination of 2 drugs; 115 mu g/kg butorphanol with 1/2 ED50 fentanyl could reach experimental combination ED50; and 88 mu g/kg butorphanol with 3/4 ED50 fentanyl could reach experimental combination ED50. Conclusion: Both fentanyl and butorphanol showed good analgesic effect on incisional pain in rats, but fentanyl was superior to butorphanol. The pharmacological mechanism of combination with ED50 of fentanyl and butorphanol showed independent joint action, and the combination efficacy was related to the dosage. (C) 2016 Elsevier Inc. All rights reserved.