Penicillin G
Penicillin V

Natural penicillins

In spite of the availability of many new antibiotics, and the progressive development of resistance in bacterial species, penicillin G (Pen G)
remains a very effective agent, although its usefulness is limited by the necessity for parenteral administration. Penicillin was isolated from Penicillium notatum by Fleming in 1928 and introduced into clinical medicine in 1941 by Florey, Chain, and associates [1-3]. The history of penicillin is recorded in a number of monographs [4-6].

The penicillin used initially was an amorphous compound containing impurities, which were introduced during the fermentative process; its
activity and dosage were expressed in units. Early penicillin was also a mixture of several penicillin compounds, designated F, G, X, and K. Pen G (benzylpenicillin) was the most satisfactory, and this is now used in a purified and crystalline form for clinical purposes.

The penicillin nucleus, 6-aminopenicillanic acid (6-APA), consists of three components – a thiazolidine ring, the b-lactam ring, and a side chain.


1. Fleming A. "On the antibacterial action of cultures of a penicillium with special reference to their use in the isolation of B. influenzae". Br. J. Exp. Pathol. 10: 226,  (1929).

2. Chain E., Florey H.W., Gardner A.D. et al. "Penicillin as a chemotherapeutic agent". Lancet 2: 226, (1940).

3. Abraham E.P. "Fleming’s discovery". Rev. Infect. Dis. 2: 140, (1980).

4. Hare R. "The Birth of Penicillin and the Disarming of Microbes". London: George Allen and Unwin,  (1970).

5. Bickel L. "Rise up to Life. A Biography of Howard Walter Florey who gave Penicillin to the World". London: Angus and Robertson, (1972).

6. Bud R. "Penicillin: Triumph and Tragedy". Oxford: Oxford University Press,  (2007).



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