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List of penicillins: Uses, common brands, and safety information

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 discovery of penicillin would later change the world of medicine as the first true modern antibiotic. Today, there are several different types of penicillins produced to treat bacterial infections. 

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

List of penicillins
Brand name (generic name) Average cash price SingleCare price Learn more
Amoxil (amoxicillin) $23.99 per 20, 250 mg tablets Get amoxicillin coupons Amoxicillin details
Augmentin (amoxicillin/clavulanate) $72.99 per 20, 500-125 mg tablets Get amoxicillin/clavulanate coupons Amoxicillin/clavulanate details
Unasyn (ampicillin/sulbactam) $110.36 per 16, 3 (2-1) gm solution reconstituted Get ampicillin/sulbactam coupons Ampicillin/sulbactam details
Dycill (dicloxacillin) $103.99 per 40, 500 mg capsules Get dicloxacillin coupons Dicloxacillin details
Bactocill (oxacillin) $104 per 10, 1 gm solution reconstituted Get oxacillin coupons Oxacillin details
Pen VK (penicillin V potassium) $40.67 per 28, 500 mg tablets Get penicillin V potassium coupons Penicillin V potassium details
Pfizerpen (penicillin G potassium) $47 per 1, 5000000 unit solution reconstituted Get penicillin G potassium coupons Penicillin G potassium details

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 is penicillin?

Penicillin belongs to a group of antibiotics that are commonly prescribed to treat bacterial infections. 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. Penicillins have strong antimicrobial activity against many different strains of bacteria. They can be administered as oral tablets, oral capsules, liquid suspensions, and intravenous (IV) injections. 

How does penicillin 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 bursting (lysis) and cell death. Because they directly kill bacteria, penicillins are considered bactericidal antibiotics. Penicillins are generally effective against gram-positive bacteria, but different penicillins can target other types of bacteria. 

What is penicillin used for?

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

Penicillin can also treat the following:

Penicillin can be effective against several types of bacteria including:

  • Listeria 
  • Neisseria
  • Shigella
  • Salmonella
  • Klebsiella
  • E. coli
  • H. influenzae
  • Pseudomonas aeruginosa
  • Bacteroides fragilis

Types of penicillin

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. Examples 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 its 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

Penicillin can be used to treat bacterial infections in adults. 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. 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. 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. 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.

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 rash, itchiness, swelling, and trouble breathing. Anaphylactic reactions require immediate medical attention. Those 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. 

Penicillin recalls

There are no current penicillin recalls as of February 2021.

Penicillin restrictions

Penicillin is not used to treat infections caused by viruses 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)

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

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.