Penicillins: use, side effects, dosage, precautions.


Penicillin is an antibiotic used to treat certain types of bacterial infections . Common side effects include diarrhea and an upset stomach, and some people may have an allergic reaction to penicillin ; the effects can range from mild to severe.

Penicillin is available in oral form for oral administration, intravenous (IV, vein), or intramuscular (IM, large muscle) injection. And there are different types of penicillin with different mechanisms of action .


All forms of penicillin are derived, at least partially, from the fungus Penicillium chrysogenum.

Scottish scientist Alexander Fleming is credited with discovering penicillin in 1929, when he realized that a fungus was killing bacterial cultures accidentally infected with "mold sap." It wasn't until 1941 that scientists were able to successfully isolate, purify, and test the drug on their first patient, ushering in the age of antibiotics.

In the 1960s, scientists were able to develop the first semi-synthetic penicillin drugs that could treat a wider range of bacterial infections. Around the same time, they began to realize the threat of penicillin resistance as mutant bacterial strains resistant to antibiotics began to emerge and spread throughout the population.

Streptococcal pneumoniae (a type of bacterial pneumonia ) and some types of Clostridium and Listeria bacteria have also become less sensitive to these antibiotics .

Overuse of antibiotics in livestock to stimulate growth is known to increase the risk of resistant bacteria, including superbugs , emerging along the food chain. As a result of this growing global concern, the United States has banned the use of antibiotics for growth. promotion of animals in 2017 .


Penicillins belong to a broader family of drugs known as beta-lactam antibiotics. These drugs have a similar molecular structure and are made up of a four-atom ring called a beta-lactam. Each type of penicillin has additional side chains that determine its activity.

Penicillins work by binding to molecules on the walls of bacteria called peptidoglycans. When bacteria divide, penicillin prevents proteins from reassembling into the cell wall properly, causing the bacterial cell to break down and die quickly.

Natural penicillins are penicillins derived directly from the fungi P. chrysogenum . There are two natural penicillins.

Semi-synthetic penicillins are made in the laboratory to resemble the chemicals found in P. chrysogenum . There are four classes of semisynthetic penicillins, including commonly prescribed antibiotics such as amoxicillin and ampicillin.

Semi synthetic

  • Aminopenicillins (ampicillin, amoxicillin, and getacillin)

  • Antistaphylococcal penicillins (cloxacillin, dicloxacillin, nafcillin, and oxacillin)

  • Broad spectrum penicillins (carbenicillin, mezlocillin, piperacillin, ticarcillin)

  • Beta-lactamase inhibitor (clavulanic acid)

Each of these types has a slightly different molecular structure and can be used differently from the others.

Some penicillins do not have direct antibacterial activity. They are used in combination therapy to help overcome resistance to penicillin. For example, clavulanic acid blocks an enzyme secreted by antibiotic resistant bacteria (beta-lactamase) that inhibits the activity of beta-lactam antibiotics .


Penicillins are used to treat bacterial infections, but not to treat viral, fungal, or parasitic infections. The drugs are usually active against gram-positive bacteria , a group of bacteria that have peptidoglycan on the outside of the cell wall. In gram-negative bacteria, the peptidoglycan layer is below the lipid cell layer, making it difficult for the drug to access the molecule.

The list of gram-positive bacteria that can be treated with penicillins includes bacteria of the genus Clostridium, Listeria, Neisseria, Staphylococcal, and Streptococcal .

Natural penicillins (penicillin G and penicillin V) are still used today and are suitable for treating some common and unusual bacterial infections.

In contrast, semisynthetic antibiotics like amoxicillin, one of the most commonly prescribed antibiotics today, can be used to treat a wide range of respiratory infections, skin infections, and bacterial infections such as H. pylori , Lyme disease, and acute otitis . media .

Not by label

Penicillin misuse is common, although more often with medications such as amoxicillin and ampicillin than with natural penicillins. Unauthorized use includes treatment of patients with sepsis and newborns with acute respiratory distress syndrome . In no case are medications indicated for this use, but they are often considered necessary when no other treatment options are available .

Penicillin G is sometimes used unauthorized to treat prosthetic joint infections, Lyme disease, and leptospirosis . Penicillin V is sometimes used unauthorized to treat Lyme disease and otitis media , or to prevent infections in people who have had stem cell transplants .

Before drinking

Penicillin can be very effective when used correctly. Still, there are times when the drug is not effective in clearing the infection. In such cases, the antibiotic susceptibility test (also known as an antibiotic susceptibility test) can be used to determine if a person's infection is responding to penicillin.

The test begins by growing bacteria from a swab of body fluid and then directly exposing the bacteria to various types of penicillin in the laboratory. Antibiotic susceptibility testing is often used for people with community-acquired pneumonia who are at high risk of serious illness or death.

Precautions and contraindications.

Penicillins are contraindicated if you have previously been allergic to any drug in the penicillin family. It should also be used with extreme caution if you've ever had a severe hypersensitivity reaction to medications in the past, including anaphylaxis , Stevens Johnson syndrome (SJS), or toxic epidermal necrosis (TEN).

If you have had an allergic reaction to penicillin G or penicillin V in the past, you may, but need not, be allergic to semi-synthetic penicillins such as amoxicillin or ampicillin.

Other beta-lactam antibiotics should be used with caution in people allergic to penicillin because there is a risk, albeit small, of cross-reaction allergy. This includes cephalosporin antibiotics such as keflex (cephalexin), maxipim (cefepime), rocefin (ceftriaxone), and suprax (cefixime).

If you are concerned that you may be allergic to penicillin, you can have a skin allergy test to see if it responds to a small amount of the drug that is placed under the skin.

Penicillin should also be used with extreme caution in acute renal (renal) failure . Penicillin is excreted primarily through the kidneys, and decreased kidney function can lead to accumulation of the drug to toxic levels. Subsequent overdose of penicillin can cause symptoms of agitation, confusion, stupor, abnormal spasms, and, in rare cases, coma.


The recommended dose of penicillin G and penicillin V may vary depending on the disease and the age of the person to be treated.

Doses are measured in several different ways depending on the formulation. In adults, medication is usually measured in units or milligrams (mg). For children, the dose can be calculated in milligrams per kilogram of body weight per day (mg / kg / day) or in units per kilogram of body weight per day (units / kg / day).

Drug, remedy, medication Indication Recommended dose
Penicillin G anthrax A minimum of 8 million units per day in four doses.
Diphtheria Adults: 2 to 3 million units per day in divided doses for 10 to 12 days.
Children: 150,000 to 250,000 units / kg / day in four divided doses over 7-14 days.
Endocarditis Adults: 15 to 20 million units per day for 4 weeks.
Children: 150,000 to 300,000 units / kg / day, divided into four to six doses (the duration depends on the severity of the disease).
Gangrene 20 million units per day
Meningitis Adults: 14 to 20 million units per day for 2 weeks.
Children : 150,000 to 300,000 units / kg / day, divided into four to six doses (the duration depends on the severity of the disease).
Pneumonia Adults: 5 to 24 million units per day, divided into four to six doses (the duration depends on the severity of the disease).
Syphilis Adults: 12 to 24 million units per day every four hours for 10 to 14 days.
Children: 200,000 to 300,000 units / kg / day in four to six divided doses over 10 to 14 days.
Penicillin V Dental abscess 250-500 mg every 6 hours for 5-7 days
Erysipelas 500 mg every 6 hours as needed
Rheumatic fever Adults: 250 mg every 12 hours as needed.
Children: 125 to 250 mg every 12 hours as needed.
Strep throat Adults: 500 mg every 12 hours or 250 every 6 hours for 10 days.
Children: 250 to 500 mg every 8-12 hours for 10 days.
Staphylococcal skin infections 250 to 500 mg every 6-8 hours (duration depends on the severity of the disease)


If you have kidney disease, you may need a lower dose of penicillin to prevent drug toxicity. A dose reduction is generally recommended when creatinine clearance (a measure of kidney function ) is less than 10 milliliters per minute (ml / min).

On the other hand, if you are being treated with hemodialysis , you may need a higher dose because hemodialysis can speed up the removal of penicillin from your blood.

How to take and store

Penicillin G

Penicillin G is available as a premixed solution or as a reconstituted powder with sterile water for injection. The premix solution can be stored in the refrigerator or freezer, and the powdered formulation can be safely stored at room temperature.

Penicillin G injections cannot be given alone.

Penicillin V

Penicillin V is available as an oral tablet or as a cherry-flavored powder mixed with water. Both can be safely stored at room temperature. Once reconstituted, the powder must be refrigerated and discarded after 14 days.

Penicillin V should be taken on an empty stomach to ensure maximum absorption. It should be taken at least one hour before meals or at least two hours after meals.

If you miss a dose of penicillin V, take it as soon as you remember. If it is close to your next dose, skip the dose and continue as usual. Never double your dose.

Use as directed

Always take penicillin as directed and complete. Don't stop because you feel good. You must complete the entire course to destroy all bacteria. After stopping treatment, a small number of remaining bacteria may multiply.

Side effects

Most of the side effects of penicillin are mild and temporary and go away on their own without treatment. But sometimes the side effects can be serious, even life-threatening, and require emergency treatment.


The most common side effects of penicillins (affecting at least 1% of users):

Fever and angioedema (tissue edema) may also occur, but are less common.

Severe form

One of the most serious problems associated with penicillin use is the risk of a life-threatening total body allergy known as anaphylaxis . True penicillin-induced anaphylaxis affects one to five in 100,000 people .

Anaphylaxis can cause serious harm if it is not treated. This can lead to shock, coma, respiratory or heart failure, and even death.

When to call 911

Seek emergency care if you experience some or all of the symptoms of anaphylaxis after taking a dose of penicillin:

  • Difficulty breathing
  • Wheezing
  • Dizziness, lightheadedness, or fainting
  • Severe rash or hives
  • Fast or irregular heartbeat
  • Swelling of the face, tongue, or throat
  • Feeling of impending doom

In rare cases, penicillins can cause acute interstitial nephritis , an inflammatory kidney disease most commonly caused by an abnormal immune response to medications. Symptoms include nausea, rash, fever, drowsiness, decreased urine output, fluid retention, and vomiting. Most cases are mild, but some can become serious and cause acute kidney damage .

Penicillins, like all antibiotics, are associated with an increased risk of Clostridium difficile diarrhea . This is because antibiotics kill bacteria that are normally present in the intestines, allowing the C. difficile bacteria to multiply. Most cases are mild and easy to treat, but C. difficile is known to rarely cause severe fulminant colitis , toxic megacolon , and death.

Warnings and interactions

Penicillins are generally considered safe during pregnancy and while breastfeeding. There is no evidence in humans, but studies in animals have shown no risk of fetal injury.

If you are pregnant, planning to become pregnant, or breastfeeding, speak with your doctor to fully understand the benefits and risks of using penicillin.

Various drugs can also interact with penicillin, often competing for renal clearance. This can increase the concentration of penicillin in the blood and also increase the risk of side effects and drug toxicity. Other medications can speed up the removal of penicillin from the body and reduce the effectiveness of the drug.

Medications that can interact with penicillin include:

To avoid interactions, always tell your doctor about any medications you are taking, whether prescription, over-the-counter, dietary, herbal, or recreational.

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