Penicillin
Overview
The penicillins (pen-uh-SILL-ins) are a class of antibiotic compounds derived from the molds Penicillium notatum and Penicillium chrysogenum. The class contains a number of compounds with the same basic bicyclic structure to which are attached different side chains. That basic structure consists of two amino acids, cysteine and valine, joined to each other to make a bicyclic ("two-ring") compound. The different forms of penicillin are distinguished from each other by adding a single capital letter to their names. Thus: penicillin F, penicillin G, penicillin K, penicillin N, penicillin O, penicillin S, penicillin V, and penicillin X. A number of other antibiotics, including ampicillin, amoxicillin, and methicillin, have similar chemical structures.
Key Facts
Other Names:
Not applicable; see Overview
Formula:
(CH3)2C5H3NSO(COOH)NHCOR, where R represents any one of a number of substituted groups; see Overview
Elements:
Carbon, hydrogen, oxygen, nitrogen, sulfur
Compound Type:
Bicyclic acid (organic)
State:
Solid
Molecular Weight:
Varies; see Overview g/mol
Melting Point:
Varies; see Overview
Boiling Point:
Not applicable; all forms decompose when heated above their melting points
Solubility:
Slightly soluble in water; soluble in ethyl alcohol, ether, chloroform and most organic solvents
Penicillin was discovered accidentally in 1928 by the Scottish bacteriologist Alexander Fleming (1881–1995). Fleming noticed that a green mold, which he later identified as Penicillium notatum, had started to grow on a petri dish that he had coated with bacteria. As the bacteria grew towards the mold, they began to die. At first, Fleming saw some promise in this observation. Perhaps the mold could be used to kill the bacteria that cause human disease. His experiments showed, however, that the mold's potency declined after a short period of time He was also unable to isolate the antibacterial chemical produced by the mold. He decided that further research on Penicillium was probably not worthwhile.
As a result, it was not until a decade later that Penicillium's promise was realized. In 1935, English pathologist Howard Florey (1898–1968) and his biochemist colleague Ernst Chain (1906–1970) came across Fleming's description of his experiment and decided to see if they could isolate the chemical product produced by Penicillium with anti-bacterial action. They were eventually successful, isolating and purifying a compound with anti-bacterial action, and, in 1941, began trials with human subjects to test its safety and efficacy (ability to kill bacteria). The successful conclusion of those trials not only provided one of the great breakthroughs in the human battle against infectious diseases, but also won for Florey, Chain, and Fleming the 1945 Nobel prize for Physiology or Medicine.
How It Is Made
Penicillins are classified as biosynthetic or semi-synthetic. Biosynthetic penicillin is natural penicillin. It is produced by culturing molds in large vats and collecting and purifying the penicillins they produce naturally. There are six naturally occurring penicillins. The specific form of penicillin produced in a culturing vat depends on the nutrients provided to the molds. Of the six natural penicillins, only penicillin G (benzylpenicillin) is still used to any extent.
Semi-synthetic penicillins are produced by making chemical alterations in the structure of a naturally occurring penicillin. For example, penicillin V is made by replacing the -CH2C6H5 group in natural penicillin G with a -CH2OC6H5 group.
Common Uses and Potential Hazards
Penicillins are prescription medications used to treat a variety of bacterial infections, including meningitis, syphilis, sore throats, and ear aches. They do so by inactivating an enzyme used in the formation of bacterial cell walls. With the enzyme inactivated, bacteria can not make cell walls and die off. Penicillins do not act on viruses in the same way they do on bacteria, so they are not effective against viral diseases, such as the flu or the common cold.
Interesting Facts
- The discovery of penicillin's antibacterial action came at just the right time: the onset of World War II. The new drug made possible the saving of untold numbers of lives. As just one example, about three-quarters of all soldiers who developed bone infections as a result of wounds suffered in World War I died of those infections. By contrast, no more than about 5 percent of those who developed similar infections in World War II died. The availability of penicillin to treat those wounds in World War II made the difference in those survival rates.
A number of side effects are related to the use of penicillin. These side effects include diarrhea, upset stomach, and vaginal yeast infections. In those individuals who are allergic to penicillins, side effects are far more serious and include rash, hives, swelling of tissues, breathing problems, and anaphylactic shock, a life-threatening condition that requires immediate medical treatment.
Penicillin may alter the results of some medical tests, such as those for the presence of sugar in the urine. Penicillin can also interact with a number of other medications, including blood thinners, thyroid drugs, blood pressure drugs, birth control pills, and other antibiotics, in some cases decreasing their effectiveness.
Once promoted as wonder drugs, the use of penicillins has declined slowly because of the spread of antibiotic resistance. Antibiotic resistance occurs when new strains of bacteria evolve that are resistant to existing types of penicillin. One reason that antibiotic resistance has become a problem is the extensive and often unnecessary use of penicillins. When they are prescribed for colds and the flu, for example, they have no effect on the viruses that cause those diseases, but they encourage the growth of bacteria more able to survive against penicillins.
Words to Know
Refers to a molecule in which the atoms are arranged so as to look like two rings. Natural; made from a living organism. Produced by making chemical alterations in the structure of a naturally occurring organism.For Further Information
"β-Lactam Antibiotics: Penicillins." The Merck Manual of Diagnosis and Therapy. Chapter 153. Available online at http://www.merck.com/mrkshared/mmanual/section13/chapter153/153b.jsp (accessed on October 23, 2005).
Chain, E. B. "The Chemical Structure of the Penicillins." Nobel Lecture, March 20, 1945. Available online at http://nobelprize.org/medicine/laureates/1945/chain-lecture.pdf (accessed on October 23, 2005).
Moore, Greogry A., and Ollie Nygren. "Penicillins." The Nordic Expert Group for Criteria Documentation of Health Risks from Chemicals. http://ebib.arbetslivsinstitutet.se/ah/2004/ah2004_06.pdf (accessed on October 23, 2005).
Ross-Flanigan, Nancy. "Penicillins." Gale Encyclopedia of Medicine. Edited by Jacqueline L. Longe and Deidre S. Blanchfield. 2nd ed. Detroit, MI: Gale, 2002.
"Tom Volk's Fungus of the Month for November 2003." http://botit.botany.wisc.edu/toms_fungi/nov2003.html (accessed on October 23, 2005).
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