Traws Pharma Inc. (NASDAQ:TRAW) experienced a significant market reaction after announcing that the U.S. Food and Drug Administration has placed tivoxavir marboxil - its investigational influenza prevention candidate - on clinical hold. The company said the action followed FDA concerns centered on the mutagenicity component of the compound's data package, prompting the regulator to promise a formal communication of its concerns and recommended mitigation steps by March 16, 2026.
The company described tivoxavir marboxil as a CAP-dependent endonuclease inhibitor being developed as a once-monthly oral tablet intended to prevent influenza. While Traws noted that the clinical hold applies to activity within the United States, it emphasized that studies conducted outside the U.S. are not directly affected by the FDA's decision. Nonetheless, the hold represents a material setback for one of the company's leading pipeline programs.
Prior to the hold, Traws had filed an investigational new drug (IND) application aimed at enabling review by the Biomedical Advanced Research and Development Authority (BARDA) for potential inclusion of tivoxavir marboxil in a strategic stockpile for treatment of avian influenza. The clinical hold therefore clouds that regulatory pathway in the U.S. pending the FDA's forthcoming guidance.
Alongside the announcement about tivoxavir marboxil, Traws provided an update on ratutrelvir, its oral, ritonavir-free Mpro/3CL protease inhibitor for COVID-19. The company said completed analysis of its Phase 2 study showed ratutrelvir had a differentiated profile versus PAXLOVID, with fewer adverse events, no observed viral rebounds, and an equivalent time to sustained symptom resolution.
The company also reported progress in pre-clinical development of the tablet formulation of tivoxavir marboxil, stating that the formulation showed a 30% increase in exposure compared with a prototype formulation. Traws suggested that this higher exposure could potentially support 28-day protection against seasonal and pandemic influenza variants, a claim described in the company update but subject to the outstanding regulatory questions noted by the FDA.
Market response was immediate: the company's shares declined sharply on news of the clinical hold. The FDA's scheduled communication by March 16, 2026 will outline the agency's specific concerns and suggested next steps, leaving the near-term U.S. regulatory path for tivoxavir marboxil uncertain.
Given these developments, Traws faces a period of regulatory engagement to resolve the mutagenicity issues identified by the FDA, while continuing development work outside the United States and advancing its COVID-19 program based on the reported Phase 2 findings.