A few common cephalexin side effects include diarrhea, unexplained rash, and nausea. This part of the eMedTV Web site also describes serious side effects -- like itching, peeling of skin, and blood in stools -- and what to do if they occur. Amoxicillin (Amoxil) is a prescription drug used for treating bacterial infections. It attacks the membrane around bacteria, which stops bacteria from growing. Amoxicillin is a penicillin antibiotic that fights bacteria. Amoxicillin is used to treat many different types of infection caused by bacteria, such as tonsillitis, bronchitis, pneumonia, gonorrhea, and infections of the ear, nose, throat, skin, or urinary tract. Learn about the potential side effects of amoxicillin. Includes common and rare side effects information for consumers and healthcare professionals. Amoxicillin is used to treat certain infections caused by bacteria, such as pneumonia; bronchitis (infection of the airway tubes leading to the lungs); and infections of the ears, nose, throat, urinary tract, and skin. For most infections, you'll start to feel better in a few days. The most common side effects of amoxicillin are feeling sick (nausea) and diarrhoea. Pictures of Amoxil (Amoxicillin), drug imprint information, side effects for the patient. Amoxil (amoxicillin) is a penicillin-type antibiotic used to treat infections caused by bacteria that are B-lactamase negative (B-lactamase positive bacteria are usually resistant to Amoxil); these infections usually occur in the skin, lungs, urinary tract and eye, ears, nose, and throat. Amoxicillin side effects. Amoxicillin is a penicillin antibiotic used to treat bacterial infections, including bronchitis, pneumonia, and infections of the ear, nose, throat, skin, and urinary tract.