No Significant Improvement in Six-Minute Walk Distance as Tenax Heart Failure–Associated Pulmonary Hypertension Drug Fails Phase 3 Trial

For patients contending with both cardiac filling pressure and the burden on the pulmonary circulation, completing a six-minute walk may be the most direct test of treatment efficacy. Oral levosimendan (TNX-103), developed by Tenax Therapeutics, failed to significantly improve six-minute walk distance compared with placebo in the pivotal Phase 3 LEVEL trial, weakening the core evidence supporting this late-stage candidate’s path to market.

LEVEL is a multicenter, randomized, double-blind, placebo-controlled trial in patients with pulmonary hypertension associated with heart failure with preserved ejection fraction (PH-HFpEF). Trial registry information and the study design paper indicate that the study planned to enroll approximately 230 participants to compare once-daily oral TNX-103 with placebo. The primary endpoint was the change from baseline in six-minute walk distance after 12 weeks of treatment.

PH-HFpEF lies at the intersection of heart failure and pulmonary vascular disease: patients’ cardiac contraction fraction appears preserved, yet the heart has difficulty filling normally during diastole, while pressure in the pulmonary circulation also rises, often causing shortness of breath and limited physical activity. Multiple conventional pulmonary vasodilator treatments have previously failed to demonstrate benefit in this patient population, making LEVEL one of the few highly anticipated late-stage studies.

Levosimendan has both calcium-sensitizing and ATP-sensitive potassium channel-activating effects. Researchers had hoped it could improve support for myocardial contraction and reduce circulatory burden during exercise by modulating venous capacitance and splanchnic vasoconstriction. The earlier HELP study had shown a signal in exercise tolerance, prompting the team to select six-minute walk distance as LEVEL’s primary endpoint.

However, the signal observed in the earlier trial did not translate into a statistically significant overall benefit in this larger, more rigorously controlled Phase 3 study. The result not only affects the registration prospects of TNX-103 but also reminds researchers that the pathological mechanisms of PH-HFpEF may be highly heterogeneous, and that a single pharmacological pathway may not be sufficient to produce a measurable improvement in daily activity capacity across the overall patient population.

Currently available public information remains focused on whether the primary endpoint was met and is not yet sufficient to fully assess the actual difference in walking distance between groups, safety, secondary endpoints, or whether specific patient subgroups showed consistent signals. Only after more complete data and prespecified analyses are released will it be possible to clarify whether this failure reflects an insufficient drug effect, dilution of efficacy by differences among patients, measurement variability, or a combination of these factors; any subgroup findings will also still require validation in independent studies.