An effective dose of valdecoxib in experimental mouse models of pain

The effects of selective cyclooxygenase-2 (COX-2) inhibitors in biological functions are frequently investigated in animal models. However, there is little data on their analgesic efficacy in experimental animals. This study aimed to determine whether oral gavage of 5 mg/kg valdecoxib in mice is active as an analgesic at this dose and whether it is associated with therapeutic blood levels. A nonselective COX inhibitor, ketorolac, was also investigated for comparison. A total of 106 C57 BL/6N mice were administered a single oral dose of 5 mg/kg of valdecoxib, ketorolac or placebo. The antinociceptive effects of both drugs were tested using hot-plate and formalin tests. For the hot-plate test, reaction time (latency) of the mouse before jumping was recorded. The total time that the mouse spent on licking/biting the injected paw (with dilute formalin) was recorded in the formalin test. Apart from the behavioral tests, plasma concentrations of the drugs at this dose were also determined. Mice were fed with 5 mg/kg of either valdecoxib or ketorolac. Blood samples were collected between 1 and 9 h postingestion. Valdecoxib and ketorolac concentration in the plasma was determined by high performance liquid chromatography with ultraviolet detection (HPLC-UV). Effective antinociception was observed for both drugs in the hot-plate test from 75 min to 2 h after oral dosing. Also, both drug treatments showed a significantly reduced nociceptive response in the second phase in the formalin test (20-30 min after injection). Both valdecoxib and ketorolac showed plasma concentrations comparable to the therapeutic concentrations in humans. A single oral dose of valdecoxib or ketorolac (5 mg/kg) is able to produce a therapeutic analgesic effect in mice.