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How do the penicillins function?

Penicillins are a group of antibacterial drugs which target a vast array of bacteria. These were the first such medicines that doctors used. Penicillin development and manufacture has changed the face of medicine, as these medicines have saved millions of lives.

Penicillium fungi are the origins of the penicillin that can be taken orally or by injection.

Penicillins are now commonly used by people all over the world to treat illnesses and diseases.

Fast facts on penicillin

  • Penicillins were the first antibiotic that doctors used.
  • There are several antibiotics in the penicillin class.
  • Experts credit Alexander Fleming with discovering penicillins.
  • Penicillin works by interfering with bacteria cell walls.
  • Less than 1 percent of people are dangerously allergic to penicillin.


Drugs in the penicillin class work through the indirect bursting of walls of bacterial cells. We do this by acting directly on peptidoglycans, which in the bacterial cells play an important structural role.

Peptidoglycans build a mesh-like structure around the bacterial cell plasma membrane which increases the strength of the cell walls and prevents the entry of external fluids and particles into the cell.

Small holes emerge in its cell walls when a bacterium multiplies, as the cells divide. Then fill these holes with newly-produced peptidoglycans to repair the walls.

Penicillins block the struts of protein that tie peptidoglycans together. This prevents the bacterium from closing holes in the walls of its cells.

As the surrounding fluid’s water content becomes greater than that inside the bacterium, water rushes into the cell through the openings, and the bacterium bursts.


The discovery of penicillins is generally attributed to Alexander Fleming. The story goes that one day, in September 1928, he returned to his laboratory to find a Petri dish no longer in place containing Staphylococcus bacteria with its lid.

The dish had become tainted with Penicillium notatum, a blue-green slime. Fleming found there was a strong ring around the mold where the bacteria could not expand.

Fleming set the wheels in motion by finding this model and understanding its use, to produce one of the most effective drugs in medical history.

Anne Miller became the first civilian to get effective penicillin therapy in March 1942. After a miscarriage she narrowly avoided death after serious infection.

Although the first antibiotic was theoretically discovered by Fleming, scientists had to do more research before penicillins could become available for general use.

The majority of the work was carried out by scientists with a superior laboratory and a deeper understanding of chemistry than Fleming. Howard Florey, Norman Heatley, and Ernst Chain carried out the first in-depth, concentrated drug trials.

In Fleming’s acceptance speech for the Nobel Prize, he cautioned that one day, the overuse of penicillins could lead to bacterial resistance.


Contrary to popular opinion, it is not the person who develops penicillin resistance but the bacteria themselves.

A billion years ago, bacteria were around. They have encountered extreme environments during this period, and are therefore highly adaptable. We often recover very rapidly, allowing for relatively rapid genetic changes across a population.

Bacteria can develop an immunity to penicillin in three common ways:

  • Penicillinase: Sometimes, bacteria may produce penicillinase, an enzyme which degrades penicillins. This ability will spread throughout the bacterial community in a process called conjugation, through a small ring of DNA. This is the bacterial counterpart of sexual reproduction, where new genetic information is shared between individual organisms.
  • Altered bacterial structure: Many bacteria in their peptidoglycan wall can subtly change the format of the penicillin-binding proteins, so penicillins can no longer bind to it.
  • Removal of penicillins: Most bacteria grow penicillin export networks. Bacteria have efflux pumps which are used to release cell substances. Some of those pumps may be repurposed to allow the cell to dispose of penicillins.

Side effects

The most commmon side effects of penicillin-taking include:

  • diarrhea
  • nausea
  • headache
  • skin rashes and hives

Less common side effects include:

  • shortness of breath or irregular breathing
  • joint pain
  • sudden lightheadedness and fainting
  • puffiness and redness of the face
  • scaly, red skin
  • vaginal itching and discharge, due to either a yeast infection or bacterial vaginosis
  • sore mouth and tongue, sometimes with white patches
  • abdominal cramps, spasms, tenderness, or pain

Rare side effects include:

  • anxiety, fear, or confusion
  • a sense of impending doom
  • hallucinations
  • yellowing of the eyes and skin
  • a sore throat
  • unusual bleeding
  • diarrhea and reduced urination
  • convulsions


While penicillin use is widespread, there may be some problems or contraindications, as with any drug:

  • Breast-feeding: Small amounts of penicillin may be transmitted to the infant by those breast-feeding. This can lead to allergic reactions, vomiting, fungal infections and skin rash sustained by the child.
  • Interactions: Some other medications can conflict with penicillins. It is critical that you meet with a doctor before taking multiple medications.
  • Bleeding problems: Some penicillins, such as carbenicillin, piperacillin, and ticarcillin can exacerbate pre-existing bleeding issues.
  • Oral contraceptives: Penicillins may interfere with birth control pills and may increase the risk of unwanted pregnancies.
  • Cystic fibrosis: By taking piperacillin, people with cystic fibrosis are more likely to suffer fever and skin rashes.
  • Kidney disease: An increased risk of side effects is present for individuals with kidney disease.
  • Methotrexate: Methotrexate interferes with cell growth and can treat various conditions including leukemia and certain autoimmune diseases. Penicillins prevent it medication from being disposed of by the body which could lead to severe complications.
  • Phenylketonuria: Many stronger chewable amoxicillin tablets contain high aspartame levels which are converted to phenylalanine by the body. This is dangerous to anyone suffering from phenylketonuria.
  • Gastrointestinal problems: When taking penicillins, patients with a history of stomach ulcers or other intestinal disorders may be more likely to develop colitis.

Penicillin allergy

A few may have penicillin allergies.

Allergic reactions to penicillin usually cause hives, wheezing, and swelling, particularly of the face.

About 10 percent of people record penicillin allergy, but the actual figure is closer to 1 percent, and only about 0.03 percent have life-threatening allergic reactions.

Alcohol and penicillin

Many antibiotics, including metronidazole and tinidazole, have severe alcohol-reactions. That’s not the case for penicillins though.


Penicillins have saved countless lives in medicine during their usage history. Today doctors are concerned about rising antibiotic resistance, however. Only time will tell how future antibiotics will conquer that barrier.

Chukwuebuka Martins

Chukwuebuka MartinsĀ is a writer, researcher, and health enthusiast who specializes in human physiology. He takes great pleasure in penning informative articles on many aspects of physical wellness, which he then thoroughly enjoys sharing to the general public.

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