Editing Penicillin (section)

=== Developments from penicillin ===
The narrow range of treatable diseases or "spectrum of activity" of the penicillins, along with the poor activity of the orally active phenoxymethylpenicillin, led to the search for derivatives of penicillin that could treat a wider range of infections. The isolation of 6-APA, the nucleus of penicillin, allowed for the preparation of semisynthetic penicillins, with various improvements over benzylpenicillin (bioavailability, spectrum, stability, tolerance).

The first major development was ampicillin in 1961. It offered a broader spectrum of activity than either of the original penicillins. Further development yielded β-lactamase-resistant penicillins, including flucloxacillin, dicloxacillin, and methicillin. These were significant for their activity against β-lactamase-producing bacterial species, but were ineffective against the [[methicillin-resistant Staphylococcus aureus|methicillin-resistant ''Staphylococcus aureus'']] (MRSA) strains that subsequently emerged.<ref>{{cite journal | vauthors = Colley EW, Mcnicol MW, Bracken PM | title = Methicillin-Resistant Staphylococci in a General Hospital | journal = Lancet | volume = 1 | issue = 7385 | pages = 595–97 | date = March 1965 | pmid = 14250094 | doi = 10.1016/S0140-6736(65)91165-7 }}</ref>

Another development of the line of true penicillins was the antipseudomonal penicillins, such as carbenicillin, ticarcillin, and piperacillin, useful for their activity against Gram-negative bacteria. However, the usefulness of the β-lactam ring was such that related antibiotics, including the mecillinams, the carbapenems, and, most important, the cephalosporins, still retain it at the center of their structures.<ref>{{cite journal | vauthors = James CW, Gurk-Turner C | title = Cross-reactivity of beta-lactam antibiotics | journal = Proceedings | volume = 14 | issue = 1 | pages = 106–07 | date = January 2001 | pmid = 16369597 | pmc = 1291320 | doi = 10.1080/08998280.2001.11927741 }}</ref>