Traws Pharma announced positive phase 2 results showing its investigational COVID-19 antiviral ratutrelvir as a possible alternative to Paxlovid, including for ineligible patients, while advancing tivoxavir marboxil as a once-monthly oral prophylactic for seasonal influenza.
Traws Pharma has completed the clinical analysis of its 90-patient, open-label phase 2 study evaluating ratutrelvir, an investigational oral, ritonavir-free Mpro/3CL protease inhibitor, in patients with mild-to-moderate COVID-19. The study compared ratutrelvir to Paxlovid and included a treatment arm for patients ineligible for ritonavir-boosted regimens, a population that often lacks effective therapeutics and is at elevated risk for severe disease.
Results from the active-controlled trial showed that ratutrelvir demonstrated a differentiated clinical profile compared with Paxlovid, with fewer treatment-related adverse events and no observed viral rebound. Patients ineligible for Paxlovid who received ratutrelvir experienced fewer adverse events (10%) compared with those treated with Paxlovid (23.3%), and achieved faster symptom resolution, with a hazard ratio of 1.31 (95% CI, 0.78–2.20; p=0.018).
“From a clinical perspective, the completed data analysis confirms that ratutrelvir may provide a meaningful benefit across a broader range of patients, including those who are unable to receive ritonavir-boosted therapy,” Traws Pharma Chief Medical Officer Robert R. Redfield, MD, said in a statement. “The favorable tolerability profile, together with a shortened time to symptom resolution and the absence of viral rebound events in ratutrelvir-treated patients, encourages and supports the continued clinical evaluation of ratutrelvir in both acute COVID-19 and in studies designed to better understand its potential impact on longer-term outcomes.”
Redfield added that ratutrelvir’s extended dosing duration and tolerability profile could have implications beyond acute infection. “The combination of early and sustained symptom improvement, extended dosing duration, absence of viral rebound observed to date, and favorable tolerability supports the strategic hypothesis that ratutrelvir may have utility in reducing post-acute sequelae of SARS-CoV-2 infection (long COVID),” he said.
Ratutrelvir showed fewer adverse events, no viral rebound, and faster symptom resolution compared with Paxlovid, including in patients ineligible for ritonavir-based therapy.
The drug’s profile supports further study in Long COVID prevention, potentially differentiating it from existing oral antivirals.
Tivoxavir marboxil is advancing toward once-monthly influenza prevention, though US regulatory hurdles remain for its development pathway.
In parallel, Traws Pharma provided an update on tivoxavir marboxil (TXM), a CAP-dependent endonuclease inhibitor being developed as a once-monthly oral prophylactic for seasonal influenza. Pre-clinical analysis of a tablet formulation demonstrated approximately 30% higher drug exposure compared with an earlier prototype, building on Phase 1 data that showed blood levels exceeding three times the EC50 against multiple influenza variants for up to 22 days.
“Modelling of these data suggests that the tablet formulation should provide 28-day coverage, enabling a once-a-month prophylactic treatment,” Traws Pharma Chief Science Officer C. David Pauza, PhD, said in a statement. He noted that a pharmacokinetic study of the compressed tablets has been submitted under an open IND in Australia, with preparations underway for a seasonal human influenza prophylaxis challenge study in the United Kingdom.
The company also disclosed that the FDA placed its US IND for tivoxavir marboxil on clinical hold due to concerns related to mutagenicity data, with formal guidance expected by mid-March 2026. According to Redfield, the hold does not affect ongoing or planned studies outside the US, and the company is actively working with regulators to address the issue.
“Collectively, the advancement of our antiviral portfolio provides a number of significant value inflection points and could provide treatment and prevention options for clinically important viral diseases,” Traws Pharma CEO Iain Dukes, MA, DPhil, said in a statement.
