Augmentin (amoxicillin/clavulanate) is a combination antibiotic used to treat bacterial infections including sinusitis, pneumonia, ear infections, bronchitis, urinary tract infections, and infections of the skin.Side effects of Augmentin (amoxicillin/clavulanate) can include.1  nausea,2  vomiting,3  headache,ugmentin (amoxicillin/clavulanate) is a combination antibiotic used to treat bacterial infections including sinusitis, pneumonia, ear infections, bronchitis, urinary tract infections, and infections of the skin. Side effects of Augmentin (amoxicillin/clavulanate) can include. 1  nausea, 2  vomiting, 3  headache,