Traws Pharma shares fall 22.34% after-hours as FDA places tivoxavir marboxil on clinical hold over mutagenicity concerns.

Traws Pharma (TRAW) fell 22.34% in after-hours trading following the FDA placing its influenza drug tivoxavir marboxil on clinical hold due to mutagenicity concerns. This announcement overshadowed positive data from a Phase 2 trial of ratutrelvir, which showed fewer adverse events and faster symptom resolution compared to PAXLOVID. While the FDA’s hold does not halt international studies, it raises regulatory uncertainty for tivoxavir’s U.S. development, a key market. The stock’s sharp decline reflects investor concern over the FDA’s formal concerns and potential delays in advancing tivoxavir, despite favorable results for ratutrelvir and preclinical progress on the influenza tablet formulation. The FDA’s detailed feedback, expected by March 16, 2026, remains a critical next step.