"Penicillin (sometimes abbreviated PCN or pen) is a group of antibiotics derived
from Penicillium fungi.[1] They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V. Penicillin antibiotics are historically significant because they are the first drugs that were effective against many previously serious diseases, such as syphilis, and infections caused by staphylococci and streptococci. Penicillins are still widely used today, though many types of bacteria are now resistant. All penicillins are β-lactam antibiotics and are used in the treatment of bacterial infections caused by susceptible, usually Gram-positive, organisms."
"The term 'penam' is used to describe the core skeleton of a member of the penicillin antibiotics. This skeleton has the molecular formula R-C9H11N2O4S, where R is a variable side chain."
"Normal penicillin has a molecular weight of 313[6] to 334[7][8] g/mol (latter for penicillin G). Penicillin types with additional molecular groups attached may have a molar mass around 500 g/mol. For example, cloxacillin has a molar mass of 476 g/mol and dicloxacillin has a molar mass of 492 g/mol."