RESUMO
Adjuvant or co-analgesic drugs, such as antipsychotics are commonly administered in combination with one of the primary analgesics. The present study is carried out to investigate the effects of the antipsychotic drug; chlorpromazine in four animal models of induced pain and to compare its effects with diclofenac sodium and with their combination. All experiments were performed on albino mice [Balb/C] strain. Mice were evaluated for their responsiveness to noxious stimuli using four tests: tail-flick test, hot-plate test, formalin test and acetic acid-induced writhing test. These effects were measured before and one hour after intraperitoneal drug administration. In some experiments, they were followed for 6 and 24 hours. In general,chlorpromazine,on its own, showed a significant analgesic activity in heat-induced pain models [tail-flick and hot-plate tests] increasing latency by around 34% and 80% in the two tests respectively. This is compared to 83% and 88% increase by diclofenac sodium. In the early phase of chemically-induced somatic type of pain [formalin test] and visceral-type of pain [writhing test], chlorpromazine had similar effect to diclofenac sodium. When chlorpromazine was given in combination with diclofenac sodium in writhing test, it did not enhance diclofenac effect. In the other three models, chlorpromazine resulted in a significant enhancement of diclofenac effect in at least two of the remaining three pain models to an extent, ranging from 46% to 55% more than that of the diclofenac effect. Chlorpromazine showed different analgesic activity according to the type of pain model utilized. The analgesic activities were either similar to diclofenac [in writhing and formalin tests], or less than diclofenac effect in tail-flick and hot-plate tests. Chlorpromazine increased the analgesic effect of diclofenac when used in combination in tail-flick, hot-plate and formalin tests