Toxicity assessment is an important tool in drug discovery and development. PT-31 (3-(2-chloro-6-fluorobenzyl)-imidazolidine-2,4-dione) is an imidazolidine- 2,4-dione analogue of clonidine that displays a dose-dependent analgesic profile and synergism with morphine. This study investigated genotoxic and mutagenic effects of PT-31 in Swiss mice. For this, ten mice (M1:F1) per group were treated with PT-31 intraperitoneally (i.p.) at 0.5, 1.0 and 5.0 mg/kg. The dimethyl sulfoxide (0.5%) and 50 mg/kg cyclophosphamide (i.p.) were taken as negative (NC) and positive controls, respectively. The bone marrow cells were collected after 24 h, while peripheral blood after 30 min, 12 h and 24 h of the treatment for the comet assay. Micronucleus (MN) test was performed only on bone marrow cells collected after 24 h of i.p. treated animals. A hundred cells were considered for the comet assay and quantification of the index of damage and frequency of damage. Lack of genotoxicity with 0.5 mg/kg of PT-31 and DNA repair ability with 0.5 and 1.0 mg/kg doses at 12 h and 24 h in comparison to NC group was observed (P
