Amoxycillin. Computer artwork of a molecule of the antibiotic drug amoxycillin (formula C16H19N3O5S). The atoms are spherical and colour coded: carbon (blue), hydrogen (white), oxygen (red), nitrogen (light blue) and sulphur (yellow). Amoxycillin is a member of the penicillin family of drugs. Penicillin was the first antibiotic, isolated from strains of mould. All other members of the family are synthetic analogues. Amoxycillin is commonly used to treat infections such as bronchitis, gonorrhoea and ear infections, and also typhoid fever. Some people are allergic to the drug, and may develop a blotchy rash, fever and itching.