ABSTRACT
BACKGROUND: Combinations of analgesic drugs have been used as an option for treating pain because some types of pain are difficult to relieve with conventional analgesics. This group of drugs has been combined with analgesics or drugs without analgesic effect and is called adjuvant. One such drug is caffeine. METHODS: We undertook the present study to analyze if caffeine is able to potentiate the antinociceptive effect of metamizole in the formalin model. RESULTS: Metamizole produced a dose-dependent antinociceptive effect with ED(50) = 329.61 mg/kg in the formalin model. Caffeine at the following doses (3.16, 10.0, 17.8 and 31.6 mg/kg) also showed antinociceptive effect. When a subeffective dose of metamizole (100 mg/kg) was combined with caffeine (3.16, 10.0, 17.8 or 31.6 mg/kg), higher antinociceptive effects were produced than the corresponding effects produced by metamizole alone. One combination presented potentiation effect; the other combination showed antinociceptive effect that was not different from the effects of metamizole alone. Two combinations showed an effect lower than the corresponding effect produced by metamizole alone. CONCLUSIONS: Adjuvant caffeine is able to change the effect of metamizole in the inflammatory pain model, in which caffeine also presents an antinociceptive effect.