Can the ZPak be used to treat flu-like symptoms?

No, Zithromax (azithromycin) will not help treat flu like symptoms.

Zithromax is an antibiotic used to treat many different types of infections caused by bacteria, such as respiratory infections, skin infections, ear infections, and sexually transmitted diseases.

Flu like symptoms are mostly viral infections therefore Zithromax won't really help.

https://www.drugs.com/mtm/zithromax-z-pak.html