Could The Medication For Ear Infection Have Causes Seizure?

My friends 4 yr old just recently had a seizure. Prior to the seizure he was diagnosed with double ear infection and was put on zithromyacin. After the seizure and being hospitalized we notices two red welts behind his ears. We still do not have any answers on why the seizure happend and all the test came back ok...Why would he have red marks and could the seizure be caused from the meds