NGX426, an Oral AMPA-Kainate Antagonist, Is Effective in Human Capsaicin-Induced Pain and Hyperalgesia

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Non-N-methyl-D-aspartate receptor subtypes modulate neurotransmitter release and mediate fast excitatory postsynaptic potentials. This study evaluated the effects of an oral prodrug to tezampanel, a selective α-amino-3-hydroxy-5-methly-4-isoxazole-proprionic acid/kainate receptor antagonist, on intradermal capsaicin-induced pain and hyperalgesia.


This was a randomized, double blind, crossover, placebo-controlled study. Eighteen subjects received 150 or 90 mg NGX426, or placebo, separated by a washout of 6 ± 2 days. In each treatment period, two intradermal injections of capsaicin were given in the volar region of alternate forearms at 30- and 120-minute drug/placebo administration. Spontaneous pain, elicited pain, and area of hyperalgesia were determined at certain time points after each injection. Subjects were asked to rate the painfulness of a 1-minute long 45°C heat stimulus (brief thermal stimulation [BTS]) applied to the anterior thigh at 4 hours and 30 minutes following drug administration, then every 30 minutes through 6 hours following drug administration.


The 150-mg dose produced a statistically definitive reduction in spontaneous pain for all time points relative to placebo. The 90-mg dose produced a statistically significant reduction for the early time point and the entire time interval. Both doses significantly reduced elicited pain at all time points. For the BTS, the 150-mg group reached statistical significance compared with placebo at the 270-minute time point only.


This study demonstrated that NGX426 reduces capsaicin-induced pain and hyperalgesia in human volunteers with low incidence of side effects that suggests that this class of drug may be effective in the treatment of clinical pain.

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