Natural<unk> s<unk>  G (benzylpenicillin) was first produced from a<unk> m fungus that occurs in nature. The strain of fungus used today for the manufacture of<unk>  G was created by genetic engineering to improve the yield in the manufacturing process. None of the other natural<unk> s (F, K, N, X, O, U1 or U6) are currently in clinical use. Semi-synthetic<unk> <unk>  V (phenoxymethylpenicillin) is produced by adding the precursor phenoxyacetic acid to the medium in which a genetically modified strain of the<unk> m fungus is being cultured. Antibiotics created from 6-APA There are three major groups of other semi-synthetic antibiotics related to the<unk> s. They are synthesised by adding various side-chains to the precursor 6-APA, which is isolated from<unk>  G. These are the antistaphylococcal antibiotics, broad-spectrum antibiotics, and antipseudomonal antibiotics. Antistaphylococcal antibiotics * Cloxacillin (by mouth or by injection) * Dicloxacillin (by mouth or by injection) * Flucloxacillin (by mouth or by injection) * Methicillin (injection only) * Nafcillin (injection only) * Oxacillin (by mouth or by injection) Antistaphylococcal antibiotics are so-called because they are resistant to being broken down by staphylococcal<unk> ase. They are also, therefore, referred to as being<unk> ase-resistant. Broad-spectrum antibiotics This group of antibiotics is called "broad-spectrum" because they are active against a wide range of Gram-negative bacteria such as Escherichia coli and Salmonella typhi, for which<unk>  is not suitable. However, resistance in these organisms is now common. * Ampicillin * Amoxycillin There are many ampicillin precursors in existence. These are inactive compounds that are broken down in the gut to release ampicillin. None of these pro-drugs of ampicillin are in current use: * Pivampicillin (pivaloyloxymethyl ester of ampicillin) * Bacampicillin * Metampicillin (formaldehyde ester of ampicillin) * Talampicillin * Hetacillin (ampicillin conjugated to acetone) Epicillin is an aminopenicillin that has never seen widespread clinical use. Antipseudomonal antibiotics The Gram-negative species, Pseudomonas aeruginosa, is naturally resistant to many antibiotic classes. There were many efforts in the 1960s and 1970s to develop antibiotics that are active against Pseudomonas species. There are two chemical classes within the group: carboxypenicillins and ureidopenicillins. All are given by injection: none can be given by mouth. Carboxypenicillins * Carbenicillin * Ticarcillin * Temocillin Ureidopenicillins * Mezlocillin * Piperacillin * Azlocillin β-lactamase inhibitors * Clavulanic acid * Sulbactam * Tazobactam
Penicillin
Carbenicillin
Extended-spectrum penicillin
Tetracycline
Phenoxymethylpenicillin
Benzylpenicillin
Piperacillin
Methicillin