Japan has given fast-tracked approval for a pioneering one-dose, anti-viral medication said to stop replication of the flu virus in the body within 24 hours of being taken. This claim makes the medication more fast-acting for a number of infection markers than any available anti-viral medication for flu.

While complete recovery time for the ill may be similar to other medications, it is said to show in trials the ability to reduce fever more quickly, the time when a person who has the flu is infectious as well as to have reduced side-effects.

Xofluza (baloxavir marboxil) is from Japanese pharmaceutical company Shionogi. Baloxavir marboxil is an endonuclease inhibitor that the company says has shown to be active against both A and B viruses.

The company is working with Swiss drug maker Roche Holding on marketing the drug globally. Shionogi will market it in Japan and Taiwan.

Roche is the maker of Tamiflu (oseltamivir), one of three anti-viral drugs approved for treatment of the flu in the United States. Tamiflu is taken in 10 doses over five days, a routine not always completed by patients, and is said best if taken within 48 hours of flu onset in terms of shortening the length of the illness.

One study showed it took a median time of four days for Tamiflu to lessen flu symptoms in patients who took it, compared to five days in those who did not take it. Research has also shown it to be most effective in patients with laboratory- confirmed cases of flu.

Tamiflu is approved for use in adults, and children two weeks of age and older. Some issues regarding its use in children were raised in Japan a number of years ago. It was first approved by the FDA in 1999. Its out-of-pocket cost for a five-day course is upwards of $100, depending on dosage, when not covered by insurance.

Tamiflu works by blocking a protein on the surface of flu viruses called neuraminidase that allows the replicated virus to spread from infected cells.

Baloxavir is said to inhibit the virus from replicating within an infected cell.

Patients between the ages of 12 and 64 were involved in a randomized, double-blind, multicenter study in which some took baloxavir, some a placebo and some oseltamivir.

The Osaka-based Shionogi had received preliminary approval of its drug in January.

The company says non-clinical studies of its drug has shown resistance to oseltamivir-resistant flu strains and avian flu strains.

Roche is reportedly planning to seek FDA approval for the drug possibly in time for next year's flu season.

Anti-viral medications are not substitutes for the flu vaccine, but are given to relieve flu symptoms, particularly in patients at high risk for other complications from influenza.