Study Background and Disease Burden
Gout represents the most prevalent form of inflammatory arthritis globally, characterized by recurrent episodes of joint inflammation due to deposition of monosodium urate crystals facilitated by hyperuricemia. Effective management hinges on sustained lowering of serum urate (sUA) levels to prevent flares and long-term joint damage. Despite advances, currently approved urate-lowering therapies such as xanthine oxidase inhibitors (e.g., allopurinol, febuxostat) and uricosurics carry limitations including incomplete efficacy, adverse reactions, and contraindications in subsets of patients. Therefore, there remains a significant unmet need for novel, effective, and well-tolerated agents for hyperuricemia management in gout.
Epaminurad is a recently developed selective inhibitor of human urate transporter 1 (hURAT1), a renal transporter responsible for reabsorption of urate in the proximal tubule. By inhibiting hURAT1, epaminurad enhances renal uric acid excretion, thereby lowering serum uric acid levels. Previous phase 1 studies demonstrated promising urate-lowering effects in healthy volunteers. The current phase 2b study aimed to evaluate the efficacy and safety of epaminurad at varying doses compared with placebo in patients with gout and elevated sUA, and to establish an optimal dosing regimen.
Study Design
This was a multicenter, randomized, double-blind, placebo-controlled, dose-finding phase 2b trial implementing a five-arm parallel structure. Eligible patients were aged 19–70 years, diagnosed with gout, and had baseline sUA ≥ 0.42 mmol/L. Participants underwent standard gout prophylaxis and therapeutic lifestyle changes as background management.
Subjects were randomized to receive once daily oral doses of epaminurad at 3 mg, 6 mg, or 9 mg, febuxostat 80 mg as an active comparator reference, or matching placebo, for a total duration of 12 weeks. The primary efficacy endpoint was the proportion of patients achieving a target sUA level below 0.36 mmol/L at week 4 post-treatment initiation. Secondary endpoints included achieving sUA < 0.30 mmol/L, and mean absolute and percent changes in sUA at multiple timepoints (weeks 4, 8, and 12). Safety assessments included monitoring adverse event rates, serum creatinine, and liver function parameters.
Key Findings
A total of 169 patients were treated (99.4% male, mean age 48.3 years, baseline sUA 0.53 mmol/L) with excellent treatment adherence exceeding 90% across all arms. The proportions of patients reaching the primary endpoint of sUA < 0.36 mmol/L at week 4 showed a clear dose-response trend with epaminurad: 9 mg (88.89%), 6 mg (71.79%), and 3 mg (54.05%), all significantly outperforming placebo (0.00%; p < 0.0001). The active comparator febuxostat achieved an 84.21% response rate.
Additional efficacy analyses revealed a significantly greater proportion of patients in all epaminurad groups achieved more stringent sUA control (<0.30 mmol/L) compared to placebo at week 4, with mean percent and absolute reductions in sUA significantly favoring epaminurad across doses. These benefits were sustained consistently at weeks 8 and 12.
Regarding safety, adverse event rates were comparable among epaminurad and placebo groups, with most events classified as mild. Importantly, no significant changes in renal function (serum creatinine) or liver enzymes were observed, supporting a favorable safety and tolerability profile over the 12-week treatment period.
The study thus identified 9 mg once daily as the most efficacious dose with a good safety margin.
Expert Commentary
Epaminurad’s potent hURAT1 inhibition represents a mechanistically novel approach in gout management by selectively targeting renal urate transport, distinct from xanthine oxidase inhibition. The pronounced dose-dependent sUA lowering and comparable efficacy to febuxostat observed in this trial underscore its therapeutic potential. The safety data are reassuring, particularly as renal and hepatic safety is pivotal given the chronic nature of gout treatment.
However, the trial population was predominantly male, limiting generalizability to women with gout. The relatively short 12-week duration did not assess long-term safety or flare frequency, necessitating further phase 3 studies. Understanding epaminurad’s performance in patients with renal impairment or comorbidities will also be critical.
Current gout management guidelines emphasize achieving target sUA levels below 0.36 mmol/L (6 mg/dL) to prevent flares and crystal deposition. Epaminurad, especially at 9 mg daily, may provide an important pharmacological addition for patients inadequately controlled or intolerant to existing agents.
Conclusion
This rigorously conducted multicenter phase 2b trial demonstrates that epaminurad is an effective and safe urate-lowering agent in patients with gout. The dose-dependent efficacy and excellent tolerability during 12 weeks of treatment support further clinical development. Epaminurad has the potential to expand therapeutic options for gout by offering targeted hURAT1 inhibition, addressing an important unmet need for effective and well-tolerated urate-lowering therapies.
References
Jun JB, Lee HS, Kim SH, Lee SG, Lim DH, Kim J, Park YB, Lim MJ, Hong SJ, Choi HJ, Lee SS, Kim HA, Hwang J, Suh CH, Han S, Choe JY, Yoo WH, Song JS. Efficacy and safety of epaminurad, a potent hURAT1 inhibitor, in patients with gout: a randomized, placebo-controlled, dose-finding study. Arthritis Res Ther. 2025 May 26;27(1):113. doi: 10.1186/s13075-025-03577-w. PMID: 40420308; PMCID: PMC12105222.
