Zithromax (anitibiotic) dosage

I have been sick for over five weeks and was finally diagnosed with a sinus infection. The doctor said that sinus infections are often stubborn and hard to get rid of with antibiotics so he prescribed 500 mg a day for ten days. That seems like a large dosage and a long time to take it. I'm only basing that on what I've been reading. The pharmacist seemed to think it was a normal amount. Is this a reasonable amount? Is it safe to take it for for ten days? I would appreciate any advice and input on this matter. Thanks! :)