A new single-dose influenza antiviral drug appears significantly better than placebo at relieving the symptoms of infection, and reduces viral load faster than does oseltamivir, new research suggests.
Baloxavir marboxil – a selective inhibitor of influenza cap-dependent endonuclease – was tested in two randomized, double-blind, controlled trials. The first was a double-blind, placebo-controlled, dose-ranging, phase 2 randomized trial of 389 Japanese adults aged 20-64 years with acute uncomplicated influenza from December 2015 through March 2016. The second was a phase 3 randomized controlled trial of 1,366 patients comparing baloxavir with placebo and oseltamivir.
The phase 2 study showed patients treated with 10 mg, 20 mg or 40 mg oral dose of baloxavir experienced a significantly shorter median time to symptom alleviation compared with placebo (54.2, 51, 49.5, and 77.7 hours, respectively), according to a paper published in the Sept. 6 edition of the.
In addition, all three doses showed significantly greater reductions in influenza virus titers on days 2 and 3, compared with placebo.
The phase 3 trial CAPSTONE-1 () was a double-blind, placebo- and oseltamivir-controlled, randomized trial that enrolled outpatients aged 12-64 years with influenza-like illness in the United States and Japan from December 2016 through March 2017. Patients aged 20-64 years received a single, weight-based oral dose of baloxavir (40 mg for patients weighing more than 80 kg, 80 mg for those weighing 80 kg or less) on day 1 only or oseltamivir at a dose of 75 mg twice daily or matching placebos on a 5-day regimen.
Patients aged 12-19 years were randomly assigned to receive either baloxavir or placebo on day 1 only, according to the researchers.
The median time to alleviation of symptoms was similar in the baloxavir (53.5 hours) and oseltamivir group (53.8 hours). However, patients taking baloxavir had significantly faster declines in infectious viral load compared with those taking oseltamivir, which was taken as a 75-mg dose twice daily for 5 days. In addition, patients who were treated with baloxavir within 24 hours of symptom onset showed significantly shorter time to alleviation of symptoms compared with placebo than did those who started treatment more than 24 hours after symptoms began.
Adverse events related to the study drug were more common among patients taking oseltamivir (8.4%) compared with those taking baloxavir (4.4%) or placebo (3.9%). In the phase 2 study, the adverse event rate was lower in the three baloxavir dosage groups compared with the placebo group. The study also showed a similar low frequency of complications requiring antibiotic treatment in both the baloxavir, oseltamivir, and placebo arms.
Some patients did show evidence of decreased susceptibility to baloxavir; for example, PA I38T/M amino acid substitutions were seen in 9.7% of the patients taking baloxavir but none of randomly selected patients in the placebo group of the phase 3 trial.
“These trials showed that single doses of the cap-dependent endonuclease inhibitor baloxavir were superior to placebo in alleviating influenza symptoms in patients with uncomplicated influenza, without clinically significant side effects,” wrote Dr. Frederick G. Hayden of the University of Virginia, Charlottesville, and his coauthors.
“The antiviral effects that were observed with baloxavir in patients with uncomplicated influenza provide encouragement with respect to its potential value in treating complicated or severe influenza infections,” they noted.
Because the treatment was inhibitory for influenza virus strains that were resistant to neuraminidase inhibitors or M2 ion-channel inhibitors, it could be a treatment option for patients infected with those viruses, the researchers added.
CAPSTONE-2, a randomized, controlled trial involving patients at high risk for influenza complications () is in progress.
The study was supported by Shionogi, which developed baloxavir. Seven authors declared fees from the pharmaceutical industry, including Shionogi. Six authors were employees of Shionogi, one also holding stock. No other conflicts of interest were declared.
SOURCE: Hayden F et al. N Engl J Med. 2018;379:913-23. .