A single oral administration of Diclofenac to humanized mice, the unchanged drug in plasma peaks at 0.25 hour and then declines with a half-life (t _1/2 ) of 2.4 hours. 4'-Hydroxy diclofenac also peaks at 0.25 hour and is undetectable within 24 hours. The plasma concentration of unchanged 4'-Hydroxy diclofenac peaks at 0.25 hour and declines rapidly in Humanized chimeric mice received of 4'-Hydroxy diclofenac (10 mg/kg; a single oral).