Penicillin G. Computer model of a molecule of the antibiotic drug penicillin G, also known as benzylpenicillin (formula: C16H18N2O4S). The atoms are colour-coded: carbon (blue), hydrogen (white), nitrogen (light blue), oxygen (red) and sulphur (yellow). This was the first penicillin, isolated from the mould Penicillium sp. in 1940, but most of this family of drugs are synthetic. Penicillin G is best given by injection, and is used to treat throat and ear infections, pneumonia and meningococcal meningitis. Some people are allergic to the penicillin drugs, and their use prompts symptoms including a rash, itching and possibly even anaphylactic shock, which can be fatal.