EMA401, an orally administered highly selective angiotensin II type 2 receptor antagonist, as a novel treatment for postherpetic neuralgia: a randomised, double-blind, placebo-controlled phase 2 clinical trial.

BACKGROUND: Existing treatments for postherpetic neuralgia, and for neuropathic pain in general, are limited by modest efficacy and unfavourable side-effects. The angiotensin II type 2 receptor (AT2R) is a new target for neuropathic pain. EMA401, a highly selective AT2R antagonist, is under development as a novel neuropathic pain therapeutic agent. We assessed the therapeutic potential of EMA401 in patients with postherpetic neuralgia.

METHODS: In this multicentre, placebo-controlled, double-blind, randomised, phase 2 clinical trial, we enrolled patients (aged 22-89 years) with postherpetic neuralgia of at least 6 months' duration from 29 centres across six countries. We randomly allocated 183 participants to receive either oral EMA401 (100 mg twice daily) or placebo for 28 days. Randomisation was done according to a centralised randomisation schedule, blocked by study site, which was generated by an independent, unmasked statistician. Patients and staff at each site were masked to treatment assignment. We assessed the efficacy, safety, and pharmacokinetics of EMA401. The primary efficacy endpoint was change in mean pain intensity between baseline and the last week of dosing (days 22-28), measured on an 11-point numerical rating scale. The primary efficacy analysis was intention to treat. This trial is registered with the Australian New Zealand Clinical Trials Registry, number ACTRN12611000822987.

FINDINGS: 92 patients were assigned to EMA401 and 91 were assigned to placebo. The patients given EMA401 reported significantly less pain compared with baseline values in the final week of treatment than did those given placebo (mean reductions in pain scores -2.29 [SD 1.75] vs -1.60 [1.66]; difference of adjusted least square means -0.69 [SE 0.25]; 95% CI -1.19 to -0.20; p=0.0066). No serious adverse events related to EMA401 occurred. Overall, 32 patients reported 56 treatment-emergent adverse events in the EMA401 group compared with 45 such events reported by 29 patients given placebo.

INTERPRETATION: EMA401 (100 mg twice daily) provides superior relief of postherpetic neuralgia compared with placebo at the end of 28 days of treatment. EMA401 was well tolerated by patients.

FUNDING: Spinifex Pharmaceuticals.