Final answer:
An antiviral medication for influenza should be started as soon as possible after symptom onset to be most effective.
Step-by-step explanation:
An antiviral medication for the treatment of influenza should be started as soon as possible after the onset of symptoms. The three main antiviral drugs used to treat influenza are inhaled zanamivir, oral oseltamivir, and intravenous peramivir. These drugs work by inhibiting the virus's neuraminidase activity, which prevents the virus from spreading to other cells and shortens the duration of illness. It is important to start antiviral treatment within 48 hours of symptom onset to be most effective.