Tenax heart drug fails late-stage trial, shares collapse nearly 90%

Tenax Therapeutics (TENX) said its experimental drug TNX-103 failed to significantly improve walking capacity versus placebo in a late-stage trial for a difficult-to-treat form of heart failure, sending its shares down nearly 90%.

The company was testing TNX-103 in patients with pulmonary hypertension associated with heart failure with preserved ejection fraction, a condition characterized by elevated blood pressure in the lungs.

Patients receiving the drug improved their six-minute walk distance by 14 meters from baseline at week 12, compared with 10.4 meters for those on placebo — a 3.5-meter difference that failed to reach statistical significance. The drug also missed a key secondary endpoint measuring symptoms and quality of life.

Cantor analyst Olivia Brayer Saunders said the readout "did not go remotely how we thought it would," describing the headline result as "ugly."

Tenax nonetheless argued that the top-line result obscured a meaningful benefit in more severely ill patients. Those who could walk less than 333 meters at enrollment showed a 26.3-meter improvement over placebo.

"We did not fail to find a treatment effect — we diluted one," chief executive Chris Giordano said on an analyst call, adding that the company had not anticipated how disease burden would influence treatment response.

Chief medical officer Stuart Rich suggested the drug may have worked "too well" in less severe patients by reducing blood volume to a degree that constrained their exercise capacity. The company also highlighted a significant decline in a blood marker of cardiac stress and reduced lung pressure as supportive signals.

TNX-103 was generally well tolerated, with serious adverse events occurring at comparable rates across both arms. There are currently no approved therapies specifically indicated for the condition.

Tenax said it plans to request a meeting with the U.S. Food and Drug Administration to discuss revisions to its development program, including protocol amendments to an ongoing second study that would exclude patients with less advanced disease.