New flu treatment: fewer doses, faster

Dear Dr. Roach: I read that a new drug, Xofluza, has been approved to treat flu. Is there something about it (if known) that might make it more useful than Tamiflu? — D.C.

Baloxavir (Xofluza) has just been approved by the Food and Drug Administration.

There are several potential advantages to baloxavir compared with oseltamivir (Tamiflu).

The first is that a single dose is effective, as opposed to the normally twice a day for five days dosing of oseltamivir.

The second benefit is that the onset of action is faster, with a decrease in the amount of infectious virus by 99.99 percent within a day.

Baloxavir works by blocking synthesis of the flu virus inside the cell.

Since it is a different mechanism of action from oseltamivir, in theory, the two drugs could be used together, perhaps in people with critical illness. That has not yet been tested.

Baloxavir is modestly effective. People got better on the drug in just over two days, compared with over three days in people who got placebo.

There is no proof of reduction in mortality, but the studies looked at otherwise healthy people, whose risk for death from influenza is low.

One concern about baloxavir is that the influenza virus developed resistance to the drug in up to 10 percent of recipients after a single dose. That raises concern that the drug may lose effectiveness in the population if it is used widely. But that theoretical concern remains to be proven.

Vaccination remains the best way of preventing flu illness, but early treatment (as fast as possible, preferably within 24 hours) with an antiviral medication can make symptoms improve a bit faster.