Pharmacokinetics, Safety, and Tolerability of Tenapanor in Healthy Chinese and Caucasian Volunteers: A Randomized, Open-Label, Single-Center, Placebo-Controlled Phase 1 Study

Background. Tenapanor is a locally acting selective sodium-hydrogen exchanger 3 inhibitor with the potential to treat sodium/phosphorus and fluid overload in various cardiac-renal diseases, which has been approved for constipation-predominant irritable bowel syndrome in the US. The pharmacokinetics (PK) of tenapanor and its metabolite tenapanor-M1 (AZ13792925), as well as the safety and tolerability of tenapanor, were investigated in healthy Chinese and Caucasian subjects. Methods. This randomized, open-label, single-center, placebo-controlled phase 1 study (https://www.chinadrugtrials.org.cn; CTR20201783) enrolled Chinese and Caucasian healthy volunteers into 4 parallel cohorts (3 cohorts for Chinese subjects, 1 cohort for Caucasian subjects). In each cohort, 15 subjects were expected to be included and received oral tenapanor (10 or 30 mg as single dose, or 50 mg as a single dose followed by a twice-daily repeated dose from Day 5 to 11, with a single dose in the morning on Day 11) or placebo in a 4 : 1 ratio. Results. 59 healthy volunteers received tenapanor 10 mg (n = 12 Chinese), 30 mg (n = 12 Chinese), or 50 mg (n = 12 (Chinese), n = 11 (Caucasian)) or placebo (n = 12, 3 per cohort). After single and twice-daily repeated doses, tenapanor plasma concentrations were all below the limit of quantitation; tenapanor-M1 appeared slowly in plasma. In single-ascending dose evaluation (10 to 50 mg) of Chinese subjects, the mean C_max, AUC_0-t, and AUC_0-∞ of tenapanor-M1 increased with increasing dose level, and AUC_0-t increased approximately dose proportionally. The C_max accumulation ratio was 1.55 to 6.92 after 50 mg repeated dose in Chinese and Caucasian subjects. Exposure to tenapanor-M1 was generally similar between the Chinese and Caucasian subjects. Tenapanor was generally well-tolerated and the safety profile was similar between the Chinese and Caucasian participants receiving tenapanor 50 mg, as measured by vital signs, physical and laboratory examination, 12-lead ECG, and adverse events. No serious adverse event or adverse event leading to withdrawal occurred. Conclusion. Tenapanor was well-tolerated, with similar PK and safety profiles between Chinese and Caucasian subjects. This trial is registered with CTR20201783.