In 1929, Alexander Fleming isolated penicillin from a strain of Penicillium notatum (84). By 1941, benzylpenicillin could be produced in sufficient quantity to treat several infected patients. Clinical trials with the agent, conducted by Florey and colleagues, were successful and during World War II, benzylpenicillin was used to treat patients with streptococcal, gonococcal, and treponemal infections. Shortages of the agent continued until the late 1940s when production of large amounts of drug became possible by a deep-fermentation procedure (85). Since then, many synthetic penicillins have been developed, but resistance to the agents has increased. Despite the emergence of resistance to penicillins and the development of other classes of anti-infective agents, the penicillins remain one of the most important anti-infective classes of drugs well into the nineties. In fact, penicillin G is still the drug of choice for many types of infections, including syphilis and certain types of endocarditis.
Chemical Structure (Figure 1)
The basic chemical structure of all penicillins consists of a beta-lactam ring, a thiazolidine ring, and a side chain (6-aminopenicillanic acid). The antibacterial activity of the penicillins lies within the beta-lactam ring. Any alteration in this ring structure forms penicilloic acid and the antibacterial activity of the compound is lost. The side chain varies with each penicillin compound and generally determines the spectrum of activity, as ciprofloxacin coverage gram positive stain well as the pharmacokinetic properties of the compound. There are several natural penicillins (penicillin dihydro F, X, and K), of which benzylpenicillin (penicillin G) is the most active and is the only natural penicillin used clinically (164).
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