Final answer:
Zanamivir (Relenza) is the most appropriate therapeutic agent for acute influenza.
Step-by-step explanation:
The most appropriate therapeutic agent for acute influenza is zanamivir (Relenza).
Zanamivir is a neuraminidase inhibitor that specifically targets influenza viruses by blocking the activity of influenza virus neuraminidase. This prevents the release of the virus from infected cells and can decrease flu symptoms and shorten the duration of illness.
Other antivirals like azithromycin, acyclovir, and tetracycline are not effective against acute influenza.