Penicillins: Uses, types, brands, and safety info

Penicillin was discovered in 1928 by Alexander Fleming, a Scottish microbiologist and physician. It was named after Penicillium mold when Fleming noticed that the mold exhibited antibacterial properties. The mold grew for a couple of weeks on a culture plate with staphylococcus bacteria, and Fleming later found that the mold was stopping the growth of the bacteria. 

The discovery of penicillin would change the world of medicine as the first true modern antibiotic. Today, several different types of penicillins are produced to treat bacterial infections. Doctors may prescribe penicillins to treat pneumonia, syphilis, and meningitis, among other bacterial infections. However, they are not used to treat viral, parasitic, or fungal infections. 

Read on to learn more about the antibiotic class of penicillins, how they are used, and what side effects they can cause. 

Other penicillins include:

• Pipracil (piperacillin)

• Zosyn (piperacillin and tazobactam)

• Timentin (ticarcillin and clavulanate)

• Ticar (ticarcillin)

• Geocillin (carbenicillin)

• Permapen (penicillin G benzathine)

• Nallpen (nafcillin)

• Floxapen (flucloxacillin)

• Natacillin (hetacillin)

• Mezlin (mezlocillin)

What are penicillins?

Penicillins are part of a broader class of antibiotics known as beta-lactam antibiotics. These antibiotics contain a beta-lactam ring as part of their chemical structure, and they have strong antimicrobial activity against many different strains of bacteria. They are administered as oral tablets, capsules, liquid suspensions, and intravenous (IV) injections. 

How do penicillins work?

Penicillin works by blocking the ability of bacteria to maintain their cell wall. The bacterial cell wall is an important structure made up of a molecule called peptidoglycan that helps the cells keep their shape. Without their cell wall, bacteria cannot survive, which leads to cell bursting (lysis) and cell death. Because they directly kill bacteria, penicillins are considered bactericidal antibiotics. Penicillins are generally effective against gram-positive bacteria, although different penicillins can target other types of bacteria. 

What are penicillins used for?

Penicillins are used to treat bacterial infections of the ear, nose, and throat. They are also used to treat bacterial infections of the sinuses, skin, lower respiratory tract, stomach, intestines, kidneys, and bladder. Penicillins should only be used to treat infections caused by bacteria that are susceptible to penicillins. 

Penicillins can also treat the following:

• Meningitis

• Endocarditis

• Pneumonia

• Gonorrhea

• Syphilis

Penicillins can be effective against several types of bacteria, including:

• Listeria 

• Neisseria

• Shigella

• Salmonella

• Klebsiella

• E. coli

• H. influenzae

• Pseudomonas aeruginosa

• Bacteroides fragilis

What are the differences between penicillins?

Various types of penicillins are available, but how do they differ? To understand how they differ, we must first look at what makes a penicillin a penicillin. All penicillins have a core structure called a beta-lactam ring that helps provide antibacterial activity. However, different penicillins have slightly different chemical structures attached to the beta-lactam ring. Penicillins are also combined with certain drugs to fight bacterial resistance.

Although they were initially effective against certain bacteria, the first penicillins started to lose effectiveness as the bacteria started to become resistant. The bacteria started producing a certain enzyme, called penicillinase or beta-lactamase, that targeted and rendered the penicillins ineffective. New penicillins were developed or combined with other drugs to overcome bacterial resistance. Some penicillins were developed to be more effective against a wider range of bacteria.  

Types of penicillins

Natural penicillins

The natural penicillins comprise the penicillin G-like antibiotics, including penicillin V potassium. These penicillins were among the first antibiotics ever used to treat bacterial infections. They work by inhibiting cell wall synthesis to kill bacteria, and they are primarily effective against gram-positive bacteria and some gram-negative bacteria. The natural penicillins include penicillin G and penicillin V. 

Aminopenicillins

Like natural penicillins, aminopenicillins work by blocking bacterial cell wall synthesis. However, they can target a broader spectrum of bacteria; aminopenicillins are effective against most gram-positive bacteria, enterococci, and some gram-negative bacilli, such as H. influenzae and E. coli. Aminopenicillins are generally combined with a beta-lactamase inhibitor like clavulanate or sulbactam to make them more effective against certain bacteria. Examples of aminopenicillins include ampicillin, amoxicillin, and hetacillin. 

Broad-spectrum (antipseudomonal) penicillins

Broad-spectrum, or antipseudomonal, penicillins are a group of penicillin antibiotics that have the same antibacterial activity as aminopenicillins plus additional activity against Pseudomonas and certain strains of Enterobacter and Serratia species. Like other penicillins, antipseudomonal penicillins are typically taken with beta-lactamase inhibitors. Antipseudomonal penicillins are usually given with another antibiotic class called aminoglycosides to treat infections caused by Pseudomonas aeruginosa. Examples of antipseudomonal penicillins include piperacillin, carbenicillin, ticarcillin, and mezlocillin. 

Beta-lactamase inhibitors 

Some bacteria produce beta-lactamase, an enzyme that inactivates beta-lactam antibiotics. Beta-lactamase inhibitors are a type of medicine that fights bacterial resistance to beta-lactam antibiotics. They are generally combined with a penicillin antibiotic to prevent penicillin from breaking down, which helps increase the antibiotic’s effectiveness. Beta-lactamase inhibitors do not have any antibacterial activity when used alone. Examples include clavulanate (or clavulanic acid), sulbactam, and tazobactam.  

Penicillinase-resistant penicillins

Penicillinase-resistant penicillins are a group of penicillins that are primarily used to treat penicillinase-producing methicillin-sensitive Staphylococcus aureus. They can also be used to treat Streptococcus pneumoniae and group A streptococcal infections, as well as certain types of methicillin-sensitive staphylococcal infections. Resistant types of these bacteria produce an enzyme called penicillinase, which can inactivate penicillin antibiotics. Examples of penicillinase-resistant penicillins include oxacillin, dicloxacillin, nafcillin, flucloxacillin, and cloxacillin. 

Who can take penicillin?

Adults

Penicillins are used to treat bacterial infections in adults. The dosage varies depending on the type of penicillin and formulation used. In adults, penicillin doses are typically measured in milligrams. 

Children

Penicillin is one of the most commonly prescribed antibiotics in children. Many common childhood infections that affect the ears, nose, and throat are usually treated with a penicillin antibiotic. In children, penicillin doses are typically calculated using milligrams per kilogram of body weight. 

Is penicillin safe?

Penicillin is generally safe for treating infectious diseases when given in appropriate doses. Antibiotics require a prescription and should only be used under the supervision of a healthcare provider. Consult with a healthcare provider to determine whether penicillin is safe for you. Tell your healthcare provider about any medical conditions you have or other medications you are taking before taking an antibiotic like penicillin.

Penicillin recalls

There are no current penicillin recalls issued by the FDA as of May 2022.

Penicillin restrictions

Penicillin is not used to treat infections caused by viruses, parasites, or fungi. In order to prevent antibiotic resistance, penicillin should only be used to treat bacterial infections that are susceptible to penicillin. Penicillin should only be used with a valid prescription from a doctor. Penicillin doses may need to be adjusted or reduced in patients with severe renal problems.  

Can you take penicillin while pregnant or breastfeeding?

Penicillin is generally safe to use during pregnancy and while breastfeeding. Studies in animals have not shown that penicillins carry a risk of causing harm to the fetus. Penicillin G is an effective antibiotic for preventing the transmission of syphilis from the mother to the fetus. A healthcare provider should be consulted for appropriate antibiotic treatment during pregnancy or breastfeeding. 

Are penicillins controlled substances?

No, penicillin is not a controlled substance.

Common penicillin side effects

The most common side effects of penicillins include:

• Diarrhea

• Nausea

• Vomiting

• Stomach upset

• Abdominal pain

• Skin rash

• Itching

• Hives

• White or black patches on the tongue or in the mouth

• Injection site reactions such as redness, itching, and swelling (when the antibiotic is administered via intravenous route)

Diarrhea

Around 5% to 35% of people taking antibiotics experience antibiotic-associated diarrhea (AAD). Penicillins, along with other antibiotics like cephalosporins, commonly cause AAD. However, diarrhea associated with antibiotics is usually mild and lasts for a few days at most. In severe cases, penicillins may cause Clostridioides difficile-associated diarrhea, which may require medical attention. In addition, penicillins can cause other gastrointestinal side effects.

Other gastrointestinal side effects

Gastrointestinal side effects are common with penicillins, such as nausea, vomiting, and indigestion. These types of side effects have been reported in over 1% of people taking penicillins. Gas, bloating, and an upset stomach are other gastrointestinal side effects that may occur while using penicillins. 

Serious penicillin side effects

Serious adverse effects of penicillins may include:

• Central nervous system toxicity

• Inflammation in the kidneys

• Low white blood cell count

• Low platelet levels

• Clostridioides difficile-associated diarrhea

• Allergic reactions

Central nervous system toxicity

High doses of penicillin may lead to central nervous system toxicity, which can manifest as seizures. The risk of central nervous system toxicity may be higher in people with renal, or kidney, problems.

Inflammation in the kidneys

Interstitial nephritis, or inflammation of the kidney tubules, is a possible serious side effect of penicillins. Symptoms of interstitial nephritis include blood in the urine, rash, and fever. If kidney problems arise while taking penicillins, a healthcare provider will typically recommend stopping the penicillin. If left untreated, irreversible kidney damage or kidney failure could result from interstitial nephritis. 

Allergic reactions

In rare cases, penicillin may cause anaphylactic reactions. Penicillin should be avoided in individuals with a history of hypersensitivity reactions to penicillin. Symptoms of anaphylaxis include a rash, itchiness, swelling, and trouble breathing. Anaphylactic reactions can develop within minutes to an hour after taking a penicillin and often require immediate medical attention. People with a history of allergic reactions to penicillin should also avoid taking penicillin derivatives, cephalosporins, carbapenems, and monobactam antibiotics. 

In cases where an alternative to a penicillin-type antibiotic will not be appropriate, a patient can undergo skin testing to assess the presence of an allergic reaction to penicillin. If the skin test is positive, a desensitization process can be started to slowly administer the antibiotic until it is tolerable and effective. 

Around 10% of children have been diagnosed with a penicillin allergy, although most children who have been diagnosed do not have a true allergy to the antibiotic. For example, gastrointestinal side effects are not considered a true allergy. 

Other serious side effects of penicillins

Low white blood cell counts, or leukopenia, is a common adverse effect of nafcillin. High doses of penicillin given intravenously may cause low platelet levels, which can increase the risk of bleeding. 

Penicillin can alter the growth of normal bacteria in the colon and cause an overgrowth of a bacteria called Clostridioides difficile (formerly known as Clostridium difficile). This type of bacteria can cause pseudomembranous colitis, or inflammation of the colon, and serious diarrhea. Although mild diarrhea is common with antibiotics, a healthcare provider should be contacted if severe diarrhea develops after using penicillin. 

Penicillins like ticarcillin and carbenicillin may need to be avoided or monitored in patients with heart or kidney problems. These types of penicillins may cause increased levels of sodium in the blood. 

How much does penicillin cost?

Many penicillin antibiotics are available in generic versions. The generic version of an antibiotic is generally cheaper than the brand name while being equally effective. Penicillin antibiotics are also covered by most Medicare and insurance plans. The average retail cost of penicillin V potassium can be around $40, depending on the dosage prescribed. 

Patients may be able to save on penicillin antibiotics through various savings programs from manufacturers and pharmacies. Discount savings cards are also available to help lower the cost of penicillin antibiotics.