I had severe flu like symptoms (fever, body aches, bronchial congestion). My doctor prescribed zythromycin as a precaution since my son currently had pneumonia. Within a day of starting the 5 day dosage, I started having severe skin sensitivity. No other way to describe it but a bad sunburn over my body. It hurt just to have clothes touch my skin. Not sure if it was from the Zpak (my doctor didn't think so) but it sure seemed coincidental if not. Pain lastest for days even after going off meds.