The present study was undertaken to evaluate the antinociceptive interaction between tramadol and xylazine. The antinociceptive effect of intraperitoneal (I.P) administration of the drug alone or in combination was evaluated using the mouse hot-plate test. Administration of tramadol in fixed dose (20mg\kg) I.P with different doses of xylazine (0, 2, 4, 8) mg\kg I.P significantly referred synergism of the antinociceptive effect of tramadol depending on the dose of xylazine. There was an

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... the antinociceptive maximum possible effect (%MPE) from (27.08%) to (85.4%). The effective dose that produce 50% antinociceptive (ED50) were evaluated for each drug alone or in combination. The present study found that the administration of tramadol and xylazine markedly reduced the median effective dose (ED50) of both drugs for antinociceptive effect in mice. The result of this study demonstrated that there was synergism (super-additive) interaction between tramadol and xylazine.