The first new flu drug in 20 years won approval Wednesday from the Food and Drug Administration.
The new antiviral, generically known as baloxavir marboxil but sold under the brand name Xofluza, is a single dose treatment. It is for use only in those aged 12 or more, the F.D.A. said, and should be taken only in the first two days after symptoms like fever, aches and sniffles appear.
The pill will cost $150, according to a spokeswoman for Genentech, which will sell Xofluza in this country. Genentech will offer coupons that lower the price to $30 for patients with health insurance and to about $90 for the uninsured.
Flu season has already begun, and last year’s was one of the most lethal in decades; about 80,000 Americans died of flu or its consequences, the Centers for Disease Control and Prevention said earlier this month.
The new drug is no miracle cure and it is not approved for young children, who are one of the most vulnerable groups, so the C.D.C. still strongly recommends that every American over the age of six months get a flu shot as soon as possible.
Several other anti-flu drugs exist — the best-known of which is oseltamivir, sold as Tamiflu — but none cure the illness quickly.
Also, the influenza virus mutates very rapidly and has split into many strains that circulate simultaneously each winter, and several have evolved resistance to older drugs.
“Having safe and effective treatment alternatives is critical,” said Dr. Scott Gottlieb, the F.D.A. commissioner, in a statement. “This novel drug provides an important additional treatment option.”
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Xofluza works in a new way, by blocking an enzyme the virus needs to copy itself. So, at least in theory, circulating flu strains resistant to earlier drugs should not have any resistance to it.
It has been shown to work against both A and B strains, which circulate each year, and it is expected to work against dangerous bird flus known to occasionally infect humans, such as the A strains of both H5N1 and A H7N9.
However, it is virtually inevitable that resistance to Xofluza will evolve as more people use it. (To prevent that, doctors treat several diseases, including H.I.V. and tuberculosis, with cocktails of three or four different drugs, but that is not the norm for flu treatment.)
Xofluza was invented by Shionogi, a Japanese company that also created the statin Crestor.
It does not cure a bout of flu as rapidly as, for example, antibiotics clear susceptible bacterial infections. But it may alleviate some symptoms and shorten the time that patients feel sick, said Dr. Debra Birnkrant, the F.D.A.’s director of antiviral products.
Xofluza was approved after two clinical trials in 1,832 patients. In both trials, those treated with it recovered more quickly than those who got a placebo. In one trial, there was no difference between Xofluza and Tamiflu.
Tamiflu, which is sold by Roche, Genentech’s parent company, is now available cheaply as a generic drug. It requires two pills a day for five days.
Xofluza’s most common side effects were diarrhea and bronchitis, the F.D.A. said.
Further research is underway to see whether it is safe and effective in children and whether it lowers rates of hospitalization and death.
In June, the F.D.A. granted Shionogi and Genentech “priority review” status, expediting the approval process because it was considered an important drug.
