A Comparative Study of Opioid Analgesics Morphine, Pentazocine, and Tramadol in Mice by Hot Plate Method

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Prevention or elimination of pain therefore depends upon employing specific measures against the causative measures for e.g. treatment of pain for peptic ulcer is affected by antacids, antispasmodics and tranquilizers but never by analgesics. But when the cause of pain is not known, the drugs acting on the central nervous system alone have to be employed for immediate symptomatic relief. Pain arising from somatic structures responds to non-narcotic analgesics such as aspirin, paracetamol, oxyphenbutazone and that arising from viscera is relieved by narcotic analgesic drugs like morphine, pethidine etc. The study was done to evaluate the efficacies of the opioid analgesics morphine, pentazocine, and tramadol by accessing the analgesic activity on blocking of pain responses in mice to thermal stimulation. The study included male swiss albino mice divided into ten groups each group consisting of six mice. First group (control) was injected with normal saline. The other groups were injected with 3 different doses using drugs morphine injected subcutaneously, pentazocine and tramadol injected intraperitoneally. The analgesic activity on blocking of pain responses in mice to thermal stimulation and jump response was evaluated using hot plate. ANOVA and Student's t test (paired) were used for statistical analysis of the data. Results were analyzed by ANOVA followed by Student's paired t test. Morphine at doses 0.25, 0.5, 1.0 mg/kg s.c increased pain threshold in mice and showed significant increase in time for jump response in comparison with the other two drugs pentazocine and tramadol.The study showed that morphine found to most potent in comparison with pentazocine, and tramadol.