Cefdinir, (Omnicef Discontinued) is an antibiotic used to treat bacterial infections such as strep throat, E. coli, staph infections, streptococcus infections, middle ear infections, tonsillitis, bronchitis, and pneumonia. Drug interactions include antacids that contain aluminum, magnesium, and iron supplements. The most common side effects include diarrhea, abdominal pain, vomiting, rash, headache, and nausea.