Objective: Lanepitant selectively blocks substance P binding to the neurokinin-1 receptor, preventing neurogenic inflammation and pain transmission. Substance P is present in synovial fluid and in excess in cerebral spinal fluid. We investigated the effect of lanepitant on pain caused by osteoarthritis to evaluate the role of neurokinin-1 blockade.
Methods: Outpatients (n = 214) with moderate to severe lower-limb osteoarthritis pain were treated for 3 weeks in a parallel, randomized double-blind study with initial doses of 20, 60, 200, or 600 mg lanepitant, 375 mg naproxen, or placebo, followed by 10, 30, 100, or 300 mg lanepitant twice a day, 375 mg naproxen twice a day, or placebo twice a day in the multiple-dose period. Pain intensity, pain relief, patient global impression, and adjunctive analgesic use were compared across treatments. Safety was evaluated with adverse events, vital signs, and laboratory assessments.
Results: There was no statistically significant difference in efficacy or safety across treatments for the initial dose assessment. After 1 week of therapy, naproxen was statistically significantly (P < .05) better than placebo and lanepitant in reducing average pain. During the second and third weeks of therapy, patients receiving naproxen continued to have statistically significantly (P < .05) less pain than those receiving placebo or lanepitant despite using significantly less adjunctive analgesic medication. There were no statistically significant differences in rates of discontinuation across treatments. Lanepitant treatment was associated with diarrhea, whereas naproxen treatment was associated with gastric discomfort. There were no clinically relevant changes in vital signs or laboratory analytes for any of the treatments.
Conclusion: Lanepitant was ineffective in relieving osteoarthritis pain, possibly because neurokinin-1 binding of substance P does not play a significant role in osteoarthritis pain or because lanepitant fails to adequately penetrate the blood-brain barrier to affect central pain perception.