Tonix's long COVID drug fails phase 2 trial in pain, but biotech holds out hope for fatigue

Tonix Pharmaceuticals’ treatment for fibromyalgia-like long COVID has failed to distinguish itself as a pain treatment. But that’s not stopping the company, for now.

The med, dubbed TNX-102 SL, didn't show a statistically significant improvement in pain symptoms compared to placebo in a phase 2 trial of patients with long COVID, according to a release Tuesday. The primary endpoint was measured using a weekly average of patient-reported worst long COVID pain intensity. The company says that treated patients “trended towards a benefit.”

Tonix is instead propping up secondary endpoint data indicating that the treatment improved sleep, fatigue and cognition. The drug, a formulation of the approved muscle relaxant cyclobenzaprine hydrochloride, showed “numerical improvements” on a number of associated measurements, though the company stopped short of saying the improvements were statistically significant.

That ambiguity is not slowing down Tonix from a hard clinical development pivot toward fatigue. The company says it intends to request an end-of-phase 2 meeting with U.S. regulators to discuss a phase 3 trial with the primary endpoint being the PROMIS fatigue scale. Tonix’s team expects that meeting to happen in the first quarter of 2024.


Boosting the company’s confidence is the fact that the National Institutes of Health (NIH) recently initiated its own package of trials, dubbed RECOVER, testing potential long COVID treatments, including Pfizer’s COVID therapy Paxlovid.

"Fatigue is the symptom of long COVID that principally overlaps with chronic fatigue syndrome/myalgic encephalomyelitis and fibromyalgia," Tonix said in this morning's release. "In the NIH-funded RECOVER study analysis, fatigue was the top featured symptom and is common in each of the four clusters."

Though the genuine efficacy of TNX-102 SL as a treatment for fatigue and poor sleep is still to be determined, the biotech reported that the med was safe and tolerable. The sole treatment-emergent side effect observed among the treatment group was a case of gastritis—irritation of the stomach lining. 

Looming over Tonix, however, is a fast-dwindling cash runway. The company spent almost $100 million in the first six months of the year, from roughly $120 million on hand as of the end of December to $25 million as of June 30. The biotech previously announced that it would be focusing resources on its central nervous system pipeline and deprioritizing work on a COVID vaccine and other preclinical programs. 

The original design of TNX-102 SL was as a treatment for fibromyalgia, with a critical phase 3 readout expected in the fourth quarter of 2023. The company said in its second-quarter earnings report in early August that if the treatment is successful, the study “may serve as the final, well-controlled efficacy trial required for submission of an NDA for approval by the FDA.”