Analgesic efficacy and pharmacokinetics of topical nimesulide gel in healthy human volunteers: double-blind comparison with piroxicam, diclofenac and placebo

Abstract

Objective: The present study was conducted to compare the analgesic efficacy of a new topical gel formulation of nimesulide (10 mg of pure drug) with that of placebo, diclofenac and piroxicam gels (10 mg of pure drug) in three parallel groups in a double-blinded, randomized fashion with vehicle placebo. The analgesic activity of nimesulide was subsequently correlated with its pharmacokinetic profile.

Methods: The drugs were applied on a fixed marked area on the skin of the right forearm. Pain stimulus was administered using a modification of the Hollander method, before and at 15, 30, 60, 120 min and 240 min post-treatment. The pain experienced by the subjects was ranked separately on the visual analogue scale (VAS) and the ten-point category scale. Antinociception induced by the treatments was evaluated through the placebo-related ratings (PRR) and total pain relief (TOTPAR) analysis. The plasma concentration of nimesulide was estimated using high-performance liquid chromatography (HPLC).

Results: Nimesulide exhibited better efficacy than diclofenac, piroxicam and placebo. It demonstrated faster onset of action in concordance with earlier studies. Peak analgesic effect was observed at 120 min post-treatment, which correlated with the pharmacokinetic profile of the drug in gel formulation. In this study, diclofenac was found to be superior to piroxicam though both drugs exhibited peak analgesic effect at 60 min post-treatment. In the modified Hollander method, a good correlation was found between the ten point category scale and the VAS, indicating that it may serve as a sensitive and reliable method for the screening of analgesic drugs.

Conclusion: The superior analgesic activity of nimesulide (as gel formulation), correlating with its pharmacokinetic profile, indicates that the topical route of administration may be a safe and effective alternative to the presently used oral and rectal routes.