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Repeat-dose toxicity studies with tramadol HCl were conducted in mice and rats administered by gavage and in dogs administered by gelatin capsule. One study in dogs compared the effects of an immediate-release formulation and extended-release tablets; the tablets were put in gelatin capsules for administration. The results of the repeat-dose toxicity studies demonstrated that treatment with tramadol HCl was well-tolerated at doses up to 150 mg/kg/day in mice (28 days), 25 mg/kg/day in rats (26 weeks), and 20 mg/kg/day in dogs (39 weeks). In general, clinical signs in mice were limited to lethargy, although high doses produced tonic seizures, and no treatment related clinical signs were observed in rats at the doses administered. No treatment related clinical signs were observed in dogs at doses up to 60 mg/kg/day for 4 weeks, but longer treatment (39 weeks) produced signs of neurotoxicity.

A 13-week bridging study was conducted in dogs to compare the toxicity of the immediate-release formulation with that of extended-release tablets (200 or 300 mg/day). The only treatment-related finding was a decrease in body weight gains for dogs treated with the immediate-release formulation; this finding was not observed in dogs treated with the extended-release formulation.

None of the toxicology studies demonstrated any treatment-related effects on hematology, clinical chemistry, or urinalysis parameters and there were no treatrnent refated macroscopic or microscopie findings or effects on organ weights.

Source: FDA [Internet]. U.S. Food and Drug Administration. Available from: http://www.fda.gov/

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