 [ Symptoms ] i was diagnosed with strep throat and given penicillin for 7 days it came back and now on zpac and it is not working it came back a few days after antibiotic was done i do not think zpac is the right antibiotic what is the most effective antibiotic for a strep throat  [ Disease ] since i do not know how you were diagnosed lab culture rapid strep test or just a look and see by your medical provider penicillin remains the treatment of choice for treating true lab diagnosed group a beta hemolytic strep also known as strep throat a z pack is really not the appropriate dose for treating strep and i do not know the dose you received of the penicillin i can say that failure of antibiotics often means that you a never had strep but a viral sore throat    in which case no antibiotic would help b you were not treated appropriately either by dosage etc for a lab diagnosed case c you are a strep carrier this can be difficult to cure by oral antibiotics or d you have monomononucleosis that clinically mimicked strep throat    in this case you need to have a lab test called an ebv panel to see if you have mono either way you need to contact your medical provider    the only one that can order any additional lab tests andor treat you further