Penicillin Totally Explained

Everything about Penicillin totally explained

Penicillin (sometimes abbreviated PCN or pen) is a group of Beta-lactam antibiotics used in the treatment of bacterial infections caused by susceptible, usually Gram-positive, organisms. “Penicillin” is also the informal name of a specific member of the penicillin group Penam Skeleton, which has the molecular formula R-C₉H₁₁N₂O₄S, where R is a variable side chain.

Discovery and history

The discovery of penicillin is attributed to Scottish scientist Sir Alexander Fleming in 1928 and the development of penicillin for use as a medicine is attributed to the Australian Nobel Laureate Howard Walter Florey.
   However, several others had noted earlier the bacteriostatic effects of Penicillium: The first published reference appears to have been in 1875, when it was reported to the Royal Society in London by John Tyndall. Ernest Duchesne documented it in his 1897 paper; however it wasn't accepted by the Institut Pasteur because of his young age. In March 2000, doctors at the San Juan de Dios Hospital in San Jose (Costa Rica) published manuscripts belonging to the Costa Rican scientist and medical doctor Clodomiro (Clorito) Picado Twight (1887-1944). The manuscripts explained Picado's experiences between 1915 and 1927 about the inhibitory actions of the fungi of genera Penic. Clorito Picado had reported his discovery to the Paris Academy of Sciences, yet didn't patent it, even though his investigation had started years before Fleming's.
   Fleming recounted later that the date of his breakthrough was on the morning of Tuesday, September 28, 1928. At his laboratory in the basement of St. Mary's Hospital in London (now part of Imperial College), Fleming noticed a halo of inhibition of bacterial growth around a contaminant blue-green mold Staphylococcus plate culture. Fleming concluded that the mold was releasing a substance that was inhibiting bacterial growth and lysing the bacteria. He grew a pure culture of the mold and discovered that it was a Penicillium mold, now known to be Penicillium notatum. Charles Thom, an American specialist working at the U.S. Department of Agriculture, was the acknowledged expert, and Fleming referred the matter to him. Fleming coined the term "penicillin" to describe the filtrate of a broth culture of the Penicillium mold. Even in these early stages, penicillin was found to be most effective against Gram-positive bacteria, and ineffective against Gram-negative organisms and fungi. He expressed initial optimism that penicillin would be a useful disinfectant, being highly potent with minimal toxicity compared to antiseptics of the day, but, in particular, noted its laboratory value in the isolation of "Bacillus influenzae" (now Haemophilus influenzae). After further experiments, Fleming was convinced that penicillin couldn't last long enough in the human body to kill pathogenic bacteria, and stopped studying penicillin after 1931, but restarted some clinical trials in 1934 and continued to try to get someone to purify it until 1940.
   In 1930 Cecil George Paine, a pathologist at the Royal Infirmary in Sheffield, attempted to treat sycosis - eruptions in beard follicles - but was unsuccessful, probably because the drug didn't get deep enough. Moving on to ophthalmia neonatorum - a gonococcal infection in babies - he achieved the first cure on 25 November 1930. He cured four patients (one adult, three babies) of eye infections, although a fifth patient wasn't so lucky.
   In 1939, Australian scientist Howard Florey (later Baron Florey) and a team of researchers (Ernst Boris Chain, A. D. Gardner, Norman Heatley, M. Jennings, J. Orr-Ewing and G. Sanders) at the Sir William Dunn School of Pathology, University of Oxford made significant progress in showing the in vivo bactericidal action of penicillin. Their attempts to treat humans failed due to insufficient volumes of penicillin (the first patient treated was Reserve Constable Albert Alexander), but they proved it harmless and effective on mice.
   Some of the pioneering trials of penicillin took place at the Radcliffe Infirmary in Oxford. On March 14 1942, John Bumstead and Orvan Hess became the first in the world to successfully treat a patient using penicillin.
   The challenge of mass-producing the drug had been daunting. On March 14 1942 the first patient was successfully treated for streptococcal septicemia with U.S.-made penicillin. Half of the total supply produced at the time was used on that one patient. By June 1942 there was just enough U.S. penicillin available to treat ten patients. A moldy cantaloupe in a Peoria, Illinois market in 1943 was found to contain the best and highest-quality penicillin after a world-wide search. The discovery of the cantaloupe, and the results of fermentation research on corn-steep liquid at the Northern Regional Research Laboratory at Peoria, Illinois, allowed the USA to produce 2.3 million doses in time for the invasion of Normandy in the spring of 1944. 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 wasn't 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 don't 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's 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.

Respiratory tract infections where compliance with oral treatment is unlikely

Cellulitis, erysipelas 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.

Production

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 won't produce the antibiotics while it's 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.

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