Penicillins are a group of antibiotics used to treat a large range of bacterial infections. They are derived from Penicillium fungi and can be taken orally or via injection.
Penicillin has saved millions of lives since its initial discovery. In 2010, more than 7.3 billion standard units of penicillin (pill, capsule, or ampoule) were consumed, worldwide.
The penicillins were the first antibacterial drugs used by doctors, and they attack a wide range of bacteria. Penicillin's discovery and consequent manufacture have changed the face of medicine.
Contents of this article:
Fast facts on penicillin
Here are some key points about penicillin. More detail and supporting information is in the main article.
- Penicillin was the first antibiotic to be used medically
- There are a number of penicillin strains used for different medical applications
- Alexander Fleming is credited with penicillin's discovery
- Penicillin works by interfering with bacteria cell walls
- Less than 1 percent of people are dangerously allergic to penicillin
Penicillin: A short history
The discovery of a mold growing in an uncovered Petri dish led to the use of penicillin to treat bacterial infections.
The discovery of penicillin's antibiotic powers is attributed to Alexander Fleming. The story goes that he returned to his laboratory one day in September 1928 to find a Petri dish containing Staphylococcus bacteria with its lid removed.
The dish had become contaminated by blue-green mold. He noted that there was a clear ring surrounding the mold where the bacteria had been inhibited from growing.
This discovery of the mold - Penicillium notatum - and his recognition of its special powers set the wheels in motion to create one of the most used drugs in medical history.
In March 1942, Anne Miller became the first civilian to be treated successfully with penicillin having almost died from a huge infection following a miscarriage.
Although Fleming often gets the accolade for having invented the first antibiotic, there was a lot of work to do before penicillin could become as commonly used and useful as it is today.
The bulk of the work was eventually carried out by scientists who had a much better-stocked laboratory and a deeper understanding of chemistry than Fleming. Dr. Howard Florey, Dr. Norman Heatley, and Dr. Ernst Chain carried out the first in-depth and focused studies.
Interestingly, and with impressive foresight, Fleming's Nobel Prize acceptance speech warned that the overuse of penicillin might, one day, lead to bacterial resistance.
How penicillin works
Penicillin works by indirectly bursting bacterial cell walls. It does this by acting directly on peptidoglycans, an important part of bacteria's structure.
The peptidoglycan in bacteria's cell walls increases their strength and keeps external fluids and particles from entering them.
Peptidoglycans form a mesh-like structure around the bacteria's plasma membrane.
When a bacterium multiplies, small holes open up in their cell walls as the cells divide. These holes are then backfilled with newly produced peptidoglycans, and the wall is reconstructed. That is unless penicillin is in the vicinity.
Penicillins inhibit the protein struts that link the peptidoglycans together in the wall. This inhibition prevents the bacterium from closing the hole in its wall.
Because of the difference in pressure between the inside of the bacterium and the surrounding fluid, water rushes into the hole and the bacterium bursts.
How do bacteria become resistant to penicillin?
Contrary to popular opinion, it is not the patient who develops resistance to penicillin but the bacteria itself.
Bacteria have been around for billions of years. During this time, they have suffered extreme environments and, as such, have a great deal of experience in adapting. Additionally, they regenerate very rapidly, making any genetic changes across a population relatively swift.
There are three common ways in which bacteria can develop an immunity to penicillin:
- Penicillinase - sometimes bacteria produce penicillinases (e.g. beta-lactamase), enzymes that degrade penicillin. This ability is then transmitted throughout the bacterial group via a plasmid (a small ring of DNA) in a process called conjugation - the bacterial equivalent of sexual reproduction, where new genetic information is shared between individuals.
- Altered bacterial structure - some bacteria subtly change the format of their peptidoglycan wall or the penicillin-binding proteins so that the penicillin can no longer bind to it.
- Penicillin removal - other bacteria develop systems to export penicillin. Bacteria have efflux pumps that are used to transport substances out of the cell. Some of these pumps can be repurposed to dispose of penicillin.
Penicillin side effects
Below are some of the side effects that have been noted during penicillin usage:
Common side effects
Headaches are a common side effect of penicillin use.
- Vaginal itching and discharge - due to either a yeast infection or bacterial vaginosis
- Sore mouth and tongue, sometimes with white patches
Less common side effects
- Shortness of breath or irregular breathing
- Joint pain
- Sudden lightheadedness and fainting
- Puffiness and redness of the face
- Rashes and hives
- Scaly, red skin
Rare side effects
- Anxiety, fear, or confusion
- Sense of impending death
- Anxiety and hallucinations
- Yellowing of the eyes and skin
- Sore throat
- Unusual bleeding
- Diarrhea and reduced urination
- Abdominal cramps, spasms, tenderness, or pain
- Nausea and vomiting
Potential problems with penicillin use
Although penicillins are widely used, as with any drug, there can be some issues or contraindications that occur:
- Breast-feeding - breast-feeding mothers may pass small amounts of penicillin to their babies. This can result in allergic reactions, diarrhea, fungal infections, and skin rash.
- Interactions - some drugs can interact with penicillin. It is important to check with a doctor before taking multiple medications.
- Bleeding problems - some penicillins (carbenicillin, piperacillin, and ticarcillin) can make pre-existing bleeding problems worse.
- Oral contraceptives - penicillins can impede the effectiveness of oral contraceptives, raising the chances of pregnancy.
- Cystic fibrosis - patients with cystic fibrosis are more prone to getting fever and skin rash when taking piperacillin.
- Kidney disease - patients with kidney disease have an increased risk of side effects.
- Methotrexate - methotrexate interferes with cell growth and is used to treat a number of conditions including leukemia and some autoimmune problems. Penicillin prevents the body from disposing of the drug, potentially leading to serious complications.
- Phenylketonuria - some stronger, chewable amoxicillin tablets have high levels of aspartame that the body converts to phenylalanine. This is dangerous for anyone with phenylketonuria.
- Gastrointestinal problems - patients with a history of stomach ulcers or other intestinal diseases might be more likely to develop colitis when taking penicillin.
Some people exhibit allergies to penicillin. Allergic reactions normally include hives, wheezing, and swelling, particularly of the face. Around 10 percent of people report an allergy to penicillin but the true figure is closer to 1 percent, and only 0.03 percent exhibit life-threatening allergic effects.
Alcohol and penicillin
Although alcohol does not interact with penicillin, it may alter how effective it is. For this reason, it is not advised that people drink alcohol with penicillin.
Alcohol and penicillin also share side effects in some people - dizziness and nausea, for instance - so in combination, the side effects could be worsened.
It is also worth noting that certain antibiotics do have serious reactions with alcohol, for instance, metronidazole and tinidazole.
Penicillin has saved countless lives throughout its impressive medical career. Modern clinicians, however, worry about the onward march of antibiotic resistance. Only time will tell how the antibiotics of the future will jump this worrying hurdle.
With medical advances moving as swiftly as they currently are, anything could be around the corner. In the words of Fleming: "one sometimes finds what one is not looking for."