The Food and Drug Administration has approved a new drug, baloxavir marboxil (Xofluza), to lessen the symptoms of influenza in patients 12 years of age and older who have been symptomatic for no more than 48 hours.

Baloxavir marboxil is a prodrug that is converted by hydrolysis to baloxavir, the active form that exerts antiinfluenza virus activity. Baloxavir inhibits an influenza virus-specific enzyme required for viral gene transcription, resulting in decreased influenza virus replication.

Baloxavir marboxil was tested in two randomized, controlled, double-blind clinical trials. In the first trial, 400 Japanese adults (ages 20 to 64 years) with flu symptoms received either baloxavir marboxil or placebo. In the second trial, 1,435 American and Japanese adults and adolescents (ages 12 to 64 years) with flu symptoms received baloxavir marboxil or placebo or the antiviral drug oseltamivir (Tamiflu). In both trials, the time to alleviation of symptoms was significantly shorter in those taking baloxavir marboxil compared with placebo. There was no difference in the time to alleviation of symptoms between baloxavir marboxil and oseltamivir in the second trial. An advantage of baloxavir marboxil is that only one dose is needed, while oseltamivir must be taken twice a day for five days.

Baloxavir marboxil is not effective against bacterial infections. Patients who are mistakenly prescribed this drug to treat a bacterial infection may become more seriously ill because antibiotic treatment was delayed. There is no clinical trial data on the safe use of baloxavir marboxil in pregnant women, nursing mothers, children under the age of 12 or who weigh less than 88 lbs. (40 kg), or adults over the age of 64.

The most common adverse effects of baloxavir marboxil are diarrhea, bronchitis, headache, nasopharyngitis, and nausea; however, in clinical trials, the incidence of these adverse effects was similar for both baloxavir marboxil and placebo.

Baloxavir marboxil is administered as one single dose. Nurses should teach patients to take the medication orally, with or without food, as soon as possible after the onset of flu symptoms, but not more than 48 hours after presentation of these symptoms. Patients should not take the drug with dairy products, calcium-fortified beverages, laxatives, antacids, or oral supplements (such as iron, zinc, selenium, calcium, or magnesium), as these will decrease the circulating dose of the drug.

For complete prescribing information, see http://www.accessdata.fda.gov/drugsatfda_docs/label/2018/210854s000lbl.pdf.