Omnicef (cefdinir) is in a group of drugs called cephalosporin (SEF a low spor in) antibiotics. It works by fighting bacteria in your body. Omnicef is used to treat many different types of infections caused by bacteria. Consumer information about the medication CEFDINIR - ORAL (Omnicef), includes side effects, drug interactions, recommended dosages, and storage information. Read more about the prescription drug CEFDINIR - ORAL. Note: This document contains side effect information about cefdinir. Some of the dosage forms listed on this page may not apply to the brand name Omnicef. Pictures of Omnicef (Cefdinir), drug imprint information, side effects for the patient. Find patient medical information for Omnicef Oral on WebMD including its uses, side effects and safety, interactions, pictures, warnings and user ratings. SIDE EFFECTS Adverse Events Clinical Trials - OMNICEF Capsules (Adult and Adolescent Patients) In clinical trials, 5093 adult and adolescent patients (3841 US and 1252 non-US) were treated with the recommended dose of cefdinir capsules (600 mg/day). Common doxycycline side effects include diarrhea, skin reaction to sunlight, or unexplained rash. While these side effects may require no medical attention, if you experience more serious problems, such as watery diarrhea or fever, stop taking the antibiotic and notify your healthcare provider immediately. Cefdinir (Omnicef) is used for treating wide range of bacterial infections, including certain types of pneumonia, sinusitis, and certain skin infections. Omnicef, the brand name for cefdinir, is a medication in a class of drugs known as cephalosporin antibiotics. Omnicef is used to treat bacterial infections such as pneumonia, bronchitis, sinusitis, tonsillitis, as well as ear and skin infections, says PDR Health. Cefdinir is an antibiotic in the cephalosporin drug class prescribed to treat infections, for example, middle ear, tonsillitis, strep throat, bronchitis, and sinusitis. Common side effects are nausea, abdominal pain, loose stools, and vaginitis. Dosage and pregnancy and breastfeeding safety information are included.