Effect of cimetidine on antinociceptive properties of morphine in mice

To study the effect of H2 receptor blockers on opioid analgesics, 50 mice were divided into 5 equal groups including control group and'those receiving morphine (5 mg / kg), cimetidine (20 mg / kg), vehicle (Normal- saline) and morphine (5 mg/kg) plus cimetidine (20 mg/kg). Hot plate test (HPT) was used to evaluate the pain response and pre-and post-drug latency time. In first stage, HPT was used twice with a4h interval and in the second stage, 15 min after subcutaneous injection of each drug. Pre- and post-drug latency time in control, morphine, cimetidine, vehicle and morphine plus cimetidine groups were 8.1±1.36 and 7.4+1.72; 6.8±0.7 and 20.6±1.73; 6.1±0.64 and 13.3±1.09; 6.4±0.65 and 6.1±0.86; and 6.8±0.47 and 25.5±2.19, respectively. Pain response (MPE%) in morphine, cimetidine and cimetidine plus morphine groups in comparison with control and vehicle groups was higher (P<0.05), highest being in cimetidine plus morphine group. As cimetidine showed antinociceptive effects and increased the antinociceptive effect of morphine, so, cimetidine would decrease the need for morphine in patients suffering from acute pains.