Zithromax for sinus infection

Is Zithromax common treatment for sinus infection? Why is Zithromax prescribed other then sinus infections?

It is like erythromycin, antibiotic. I have sinus infection often and I usually get Zithromax, but other that sinus infection it is prescribed for adults to treat certain skin infections; upper and lower respiratory tract infections, strep throat, tonsillitis, worsening of chronic obstructive pulmonary disease, and pneumonia; sexually transmitted infections of the cervix or urinary tract; and genital ulcer disease in men.