AskDefine | Define penicillin

Dictionary Definition

penicillin n : any of various antibiotics obtained from penicillium molds (or produced synthetically) and used in the treatment of various infections and diseases

User Contributed Dictionary



  1. Any of a group of broad-spectrum antibiotics obtained from Penicillium molds or synthesized; they have a beta-lactam structure; most are active against gram-positive bacteria and used in the treatment of various infections and diseases.

Extensive Definition

During World War II, penicillin made a major difference in the number of deaths and amputations caused by infected wounds among Allied forces, saving an estimated 12%-15% of lives. Availability was severely limited, however, by the difficulty of manufacturing large quantities of penicillin and by the rapid renal clearance of the drug, necessitating frequent dosing. Penicillins are actively secreted, and about 80% of a penicillin dose is cleared within three to four hours of administration. During those times, it became common procedure to collect the urine from patients being treated so that the penicillin could be isolated and reused.
This was not a satisfactory solution, however; so researchers looked for a way to slow penicillin secretion. They hoped to find a molecule that could compete with penicillin for the organic acid transporter responsible for secretion such that the transporter would preferentially secrete the competitive inhibitor. The uricosuric agent probenecid proved to be suitable. When probenecid and penicillin are concomitantly administered, probenecid competitively inhibits the secretion of penicillin, increasing penicillin's concentration and prolonging its activity. The advent of mass-production techniques and semi-synthetic penicillins solved supply issues, and this use of probenecid declined..
The chemical structure of penicillin was determined by Dorothy Crowfoot Hodgkin in the early 1940s. A team of Oxford research scientists led by Australian Howard Florey, Baron Florey and including Ernst Boris Chain and Norman Heatley discovered a method of mass-producing the drug. Chemist John Sheehan at MIT completed the first total synthesis of penicillin and some of its analogs in the early 1950s, but his methods were not efficient for mass production. Florey and Chain shared the 1945 Nobel prize in medicine with Fleming for this work, and, after WWII, Australia was the first country to make the drug available for civilian use. Penicillin has since become the most widely-used antibiotic to date, and is still used for many Gram-positive bacterial infections.

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 first major development was ampicillin, which offered a broader spectrum of activity than either of the original penicillins. Further development yielded beta-lactamase-resistant penicillins including flucloxacillin, dicloxacillin and methicillin. These were significant for their activity against beta-lactamase-producing bacteria species, but are ineffective against the methicillin-resistant Staphylococcus aureus strains that subsequently emerged.
The line of true penicillins was the antipseudomonal penicillins, such as ticarcillin and piperacillin, useful for their activity against Gram-negative bacteria. However, the usefulness of the beta-lactam ring was such that related antibiotics, including the mecillinams, the carbapenems and, most important, the cephalosporins, have this at the center of their structures. Ondred Abumbumer also made further discoveries towards penicillin

Mechanism of action

β-lactam antibiotics work by inhibiting the formation of peptidoglycan cross-links in the bacterial cell wall. The β-lactam moiety (functional group) of penicillin binds to the enzyme (DD-transpeptidase) that links the peptidoglycan molecules in bacteria, which weakens the cell wall of the bacterium (in other words, the antibiotic causes cytolysis or death due to osmotic pressure). In addition, the build-up of peptidoglycan precursors triggers the activation of bacterial cell wall hydrolases and autolysins, which further digest the bacteria's existing peptidoglycan.
Gram-positive bacteria are called protoplasts when they lose their cell wall. Gram-negative bacteria do not lose their cell wall completely and are called spheroplasts after treatment with penicillin.
Penicillin shows a synergistic effect with aminoglycosides, since the inhibition of peptidoglycan synthesis allows aminoglycosides to penetrate the bacterial cell wall more easily, allowing its disruption of bacterial protein synthesis within the cell. This results in a lowered MBC for susceptible organisms.

Variants in clinical use

The term “penicillin” is often used in the generic sense to refer to one of the narrow-spectrum penicillins, in particular, benzylpenicillin.
Benzylpenicillin, commonly known as penicillin G, is the gold standard penicillin. Penicillin G is typically given by a parenteral route of administration (not orally) because it is unstable in the hydrochloric acid of the stomach. Because the drug is given parenterally, higher tissue concentrations of penicillin G can be achieved than is possible with phenoxymethylpenicillin. These higher concentrations translate to increased antibacterial activity.
Specific indications for benzylpenicillin include: As a result, changes in product packaging have been made; specifically, the statement "Not for the Treatment of Syphilis" has been added in red text to both the Bicillin CR and Billin CR 900/300 syringe labels.
Procaine penicillin is also used as an adjunct in the treatment of anthrax.
Benzathine benzylpenicillin (rINN), also known as benzathine penicillin, is slowly absorbed into the circulation, after intramuscular injection, and hydrolysed to benzylpenicillin in vivo. It is the drug-of-choice when prolonged low concentrations of benzylpenicillin are required and appropriate, allowing prolonged antibiotic action over 2–4 weeks after a single IM dose. It is marketed by Wyeth under the trade name Bicillin L-A. Specific indications for benzathine penicillin include: nevertheless, penicillin is still the most common cause of severe allergic drug reactions.
Allergic reactions to any β-lactam antibiotic may occur in up to 10% of patients receiving that agent. Anaphylaxis will occur in approximately 0.01% of patients. However recent assessments have shown no increased risk for cross-allergy for 2nd generation or later cephalosporins. Recent papers have shown that major feature in determining immunological reactions is the similarity of the side chain of first generation cephalosporins to penicillins, rather than the β-lactam structure that they share.


The production of penicillin is an area that requires scientists and engineers to work together to achieve the most efficient way of producing large amounts of penicillin.
Penicillin is a secondary metabolite of fungus Penicillium, which means the fungus will not produce the antibiotics while it is growing, but will produce penicillin when it feels threatened. There are also other factors that inhibit penicillin production. One of these factors is the synthesis pathway of penicillin:
α-ketoglutarate + AcCoA -> homocitrate -> L-α-aminoadipic acid -> L-Lysine + β-lactam
It turns out that the by-product L-Lysine will inhibit the production of homocitrate, so the presence of exogenous lysine should be avoided in the penicillin production.
The penicillium cells are grown using a technique called fed-batch culture; this way the cells are constantly subject to stress and will produce plenty of penicillin. The carbon sources that are available are also important: Glucose will inhibit penicillin, whereas lactose does not. The pH level, nitrogen level, Lysine level, Phosphate level, and oxygen availability of the batches must be controlled automatically.
Other area of biotechnology such as directed evolution can also be applied to mutate the strains into producing a much larger number of penicillin. These directed-evolution techniques include error-prone PCR, DNA shuffling, ITCHY, and strand over-lap PCR.
Penicillin production emerged as an industry as a direct result of World War II. During the time of war, there was an abundance of jobs available on the homefront. A War Production Board was made to monitor job distribution and production . Penicillin production was a huge surplus during the time of the war especially with all the available jobs and the industry prospered. In July, 1943, the War Production Board had set up a plan to distribute mass stock of penicillin to troops fighting in Europe. At the time of this plan, 425 million units were being produced. As a direct result of the war and the War Production Board, by June 1945, over 646 billion units were being produced .


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