Xofluza (baloxavir marboxil) is the first new antiflu medication to be developed in 20 years. It works by inhibiting Cap-dependent endonuclease, an enzyme essential for influenza virus to multiply itself. It is very effective and only requires a single oral dose to work. It is effective against both influenza A and B viruses. It does need to be taken within the first 48 hours of the flu to be effective.
The only other drugs that are currently available to treat influenza are Tamiflu (taken orally for 5 days), Relenza (used trans nasally) and Rapivab (only available by IV for hospitalized patients). These drugs work on a different viral enzyme called neuraminidase. Because they have “been around for a while” some viral resistance is developing.