Allergic to keflex. can i take a z-pack safely?

Probably: Keflex is a cephalosporin, and z-pak is a macrolide. Being allergic to one class doesn't imply allergy to the other class.

YES: They are of different chemical families, so the z pack shouldn't cross react. It may, however, upset your stomach, so be prepared. Very recent evidence has shown a relationship between zithromax and some cardiac conditions, but we know all drugs have some side affects in some patients. Good luck.