Baloxavir marboxil (Xofluza), an antiviral flu treatment, has now been approved to prevent influenza after exposure to a sick individual. It can be prescribed in patients ages 12 years and older.

Approval of the drug for influenza prophylaxis is based on a small randomized, double-blind, placebo-controlled trial of 607 patients who had been exposed to the flu from a household member. Half the participants received a single dose of baloxavir and half received placebo. Efficacy was determined by the proportion of patients who developed a fever of 37.5[degrees]C (99.5[degrees]F) or higher and one respiratory symptom (cough, nasal discharge, or nasal congestion) between day 1 and day 10 following administration of baloxavir or placebo, and had a positive laboratory influenza test. Of those who received baloxavir, 1% developed confirmed flu compared with 13% of placebo recipients. All subjects in this trial were Asian and most were female. Five percent of the participants were 12 to 18 years old, 4% were over 65 years old, and the rest were between 18 and 65 years old. The mean age of the subjects was 40 years old.

Baloxavir is generally well tolerated. The most common adverse effect in the study population was nasopharyngitis (6% of those receiving baloxavir versus 7% of those given placebo). The most common adverse effects of baloxavir given to treat influenza are diarrhea, bronchitis, nausea, sinusitis, and headache.

Patients should avoid products containing calcium, aluminum, or magnesium while receiving baloxavir, as the drug may chelate with these and other polyvalent cations, reducing plasma concentrations of baloxavir and causing loss of antiviral efficacy. These products include calcium-fortified beverages; magnesium- or aluminum-containing laxatives and antacids; dairy products; and oral supplements containing calcium, iron, magnesium, selenium, or zinc.

Nurses and NPs should instruct patients and families to start drug therapy as soon as possible after exposure to the flu. Baloxavir can be taken with or without food. Dosing is based on weight, and the drug is given as either a single 40-mg dose (two 20-mg tablets) for those weighing less than 80 kg or a single 80-mg dose (two 40-mg tablets) for those weighing at least 80 kg. Baloxavir is also available as an oral suspension-for oral or enteral use-that must be reconstituted prior to dispensing to the patient. Patients should be taught to use the reconstituted drug within 10 hours of receiving it, as the bottle contains no preservatives.

For complete prescribing information for baloxavir, go to http://www.accessdata.fda.gov/drugsatfda_docs/label/2020/214410s000,210854s004s0.