Penicillins

Penicillins are a widely used group of prescription antibiotics that belong to a larger family called beta-lactam antibiotics. Discovered by Alexander Fleming in 1928, penicillin antibiotics were the first effective antibacterial medicines and remain essential in treating many infectious diseases today. Penicillins work by targeting the bacterial cell wall, making them effective against many gram-positive bacteria and some gram-negative bacteria. They are commonly prescribed for everyday bacterial infections, such as ear infections, strep throat, skin infections, and urinary tract infections. Because of their long history of use, strong safety record, and proven effectiveness, penicillins continue to play a key role in modern medicine.

Penicillins are a class of antibacterial drugs used to treat infections caused by susceptible types of bacteria. They are considered antimicrobials and are available in several different forms of penicillin, including oral tablets, capsules, liquids, and injectable formulations. Penicillins are not effective against viruses, such as the common cold or flu. These medications are often chosen because of their targeted mechanism of action, relatively low cost, and long track record of use in both children and adults.

The mechanism of action of penicillins involves stopping bacteria from building a strong bacterial cell wall. Bacteria need a rigid cell wall to survive. Penicillins bind to proteins involved in cell wall formation, which weakens the cell wall and causes the bacteria to burst and die. This action makes penicillins bactericidal, meaning they actively kill bacteria rather than just slowing their growth.

Penicillins are especially effective against gram-positive bacteria, such as streptococcal and pneumococcal species, but some also work against certain gram-negative bacteria. Over time, some bacteria have developed antibiotic resistance by producing enzymes called penicillinase or beta-lactamase, which break down penicillin. To overcome this, some penicillins are combined with beta-lactamase inhibitors, such as sulbactam, tazobactam, or clavulanate, which protect the antibiotic from these enzymes.

Natural penicillins

• Penicillin G (Pfizerpen)
• Penicillin V (Veetids)
• Penicillin V potassium (Pen-Vee K)

Aminopenicillins

• Amoxicillin (Amoxil)
• Ampicillin (Principen)

Penicillinase-resistant penicillins

• Dicloxacillin (Dynapen)
• Nafcillin (Nallpen)
• Oxacillin (Bactocill)

Extended-spectrum penicillins

• Piperacillin (Pipracil)
• Ticarcillin (Ticar)
• Carbenicillin (Geocillin)

Combination penicillins with beta-lactamase inhibitors

• Piperacillin with tazobactam (Zosyn)
• Ampicillin with sulbactam (Unasyn)
• Ticarcillin with clavulanate (Timentin)
• Amoxicillin and clavulanate (Augmentin)

Penicillins are used to treat a wide range of bacterial infections. Common uses include sinus infections, pneumonia, and strep throat caused by streptococcal bacteria. They are also prescribed for ear infections, skin and soft tissue infections, dental infections, and urinary tract infections.

Certain penicillin antibiotics are used to treat more serious conditions, including meningitis, bloodstream infections, and infections of the heart valves. Penicillin G remains the treatment of choice for syphilis. Combination penicillins with beta-lactamase inhibitors are often used in hospitals for severe or resistant infections. While penicillins are not effective against methicillin-resistant Staphylococcus aureus (MRSA), they are still important for many other bacterial illnesses.

Common side effects

• Nausea
• Vomiting
• Diarrhea
• Mild stomach pain
• Headache
• Skin rash
• Yeast infections

Serious side effects

• Hypersensitivity or allergic reactions, including anaphylaxis; symptoms include skin rash, swelling of the face, lips, or throat, and trouble breathing
• Symptoms of a severe skin reaction, like blistering or peeling, painful red or purple skin, and fever
• Severe diarrhea caused by a Clostridioides difficile (C. diff) infection

These are not all of the possible side effects of penicillins. You should always seek medical advice from your healthcare provider for any questions or concerns about your medical condition or treatment. Read all patient information, medication guides, or drug information sheets that come with this medication. You can also report adverse effects to the Food and Drug Administration at www.fda.gov/medwatch or 1-800-FDA-1088.

Although these medications are generally well-tolerated and safe, there are certain warnings, precautions, and drug interactions you should be aware of.

Warnings

Before starting penicillins, it is crucial to discuss any existing health conditions with your healthcare provider. You should be sure that your healthcare provider is aware of all your medical conditions, including if you:

• Have a known penicillin allergy or history of hypersensitivity reactions
• Have ever had an allergic reaction to beta-lactam antibiotics, including cephalosporins
• Have asthma, hay fever, or multiple allergies
• Have kidney disease, as dose adjustments may be needed
• Have liver problems
• Have a history of antibiotic-associated diarrhea or colitis
• Are being treated for serious or resistant bacterial infections
• Have been diagnosed with mononucleosis, which can increase the risk of a skin rash with amoxicillin or ampicillin
• Are pregnant, planning to become pregnant, or breastfeeding

Taking penicillins exactly as prescribed is essential. Skipping doses, sharing medication, or stopping treatment early may increase the risk of antibiotic resistance and may cause the infection to return or worsen.

Contraindications

Penicillins should not be used in people with a known serious penicillin allergy. Cross-reactivity may occur in some individuals who are allergic to cephalosporins, another class of beta-lactam antibiotics. Your healthcare provider will determine if penicillin antibiotics are appropriate based on your allergy history.

Drug interactions

When penicillins are taken with other prescription drugs, over-the-counter medications, vitamins, and supplements, it may change how they work or increase the frequency or severity of side effects. Make sure that you tell your healthcare professional about anything that you are taking to avoid any negative drug interactions, including:

• Methotrexate
• Blood thinners
• Allopurinol
• Probenecid
• Other antibiotics, including cephalosporins
• Vitamins, herbal products, or dietary supplements