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Penicillin is an FDA-approved antibiotic used to treat a variety of bacterial infections. It may also be prescribed off-label for other conditions. Penicillin is both a medication and a class of antibiotics that target bacterial infections by destroying bacteria in the body in a specific way. Penicillins can be found naturally. These natural penicillins can be purified in a lab to make penicillin medications. Alternatively, scientists can alter naturally occurring penicillins to make them more effective at destroying bacteria. These semi-synthetic penicillins are made in a lab and include penicillinase-resistant penicillins, extended-spectrum penicillins, and aminopenicillins (like amoxicillin).

Common types include penicillin V, penicillin G, amoxicillin, and ampicillin. Penicillin V, or phenoxymethylpenicillin, was approved in 1958 to treat bacterial infections of the throat, ears, chest, and skin. Today, the most common penicillin is amoxicillin, which the FDA approved on January 18, 1974, to treat infections caused by gram-positive bacteria. Penicillins can be used to treat:

Respiratory Tract Infections

Penicillin is commonly used to treat respiratory infections caused by Streptococcal bacteria, including:

• Strep throat
• Sinus infections (sinusitis)
• Scarlet fever

Ear Infections

Penicillin is FDA-approved to treat bacterial ear infections, such as:

• Otitis media (middle ear infection)
• Swimmer’s ear
• Labyrinthitis

Urinary Tract Infections (UTIs)

Certain types of penicillin are used to treat urinary tract infections caused by bacteria. If you think you have a UTI, talk to your doctor about treatment options.

Sexually Transmitted Infections (STIs)

Penicillin is an effective treatment for some STIs, including:

• Syphilis (requires an intramuscular injection)
• Gonorrhea

Dental Infections

Penicillin is also approved to treat dental abscesses (tooth infections), helping to control bacterial spread and reduce pain.

Staphylococcal skin and soft tissue infections

Penicillin is also approved to treat staphylococcal skin and soft tissue infections, helping to control bacterial spread and reduce inflammation.

Staphylococcus is a type of bacteria that can cause skin infections like boils, impetigo, and cellulitis.

Penicillin is available as both a generic and a brand-name, such as Augmentin, Unasyn, or Zosyn. It is also available in tablet, liquid, and injectable forms, making it a versatile treatment option for a range of bacterial infections.

A licensed healthcare provider—such as a nurse practitioner (NP), physician assistant/associate (PA), or medical doctor (MD)—can evaluate your symptoms and prescribe penicillin online if medically necessary. 

To see if penicillin is right for your medical condition, find a provider on Klarity Health who can evaluate your symptoms and overall health. If they determine that an antibiotic is necessary, penicillin or another suitable option can be called into any online or local pharmacy.

Penicillin V is usually well-tolerated and is an effective antibiotic for treating many different types of infections.

But, side effects can still occur. Common side effects of penicillin include nausea, vomiting, diarrhea, a mild rash, abdominal pain, and a black hairy tongue. Taking penicillin V on an empty stomach can worsen gastrointestinal symptoms; taking it with food may help. Penicillin side effects may decrease as the body adjusts to the medication.

Serious side effects, like severe allergic reactions, difficulty breathing, or swelling of the throat, require immediate medical attention. Hemolytic anemia, leukopenia, thrombocytopenia, neuropathy, and nephropathy are associated with high doses of penicillin V administered through an IV.

Penicillin can interact with medications like methotrexate and oral contraceptives. It can also interact with certain diuretics, nonsteroidal anti-inflammatory drugs (NSAIDs), and sulfa medicines. Drinking acidic fruit juices, like orange or grapefruit juice, within an hour of taking penicillin G may prevent the medicine from working properly. People with penicillin allergies, a medical history of severe kidney problems, or asthma should avoid using penicillin V. There is a slight possibility of cross-reactivity with cephalosporin allergies. Penicillin is advised to be used with caution in patients who are allergic to cephalosporin medications.

If you take any form of penicillin and have any side effects, work with your provider and consider reporting negative side effects to the FDA by visiting MedWatch or calling 1-800-FDA-1088.

Penicillin V is effective in treating a variety of bacterial infections by killing bacteria and preventing their growth. However, it isn’t effective against beta-lactamase-producing bacteria.

Doctors often prescribe Augmentin (amoxicillin/clavulanate) instead, especially for infections caused by bacteria that don’t respond to regular antibiotics, like ear and sinus infections. Other common antibiotics include metronidazole, azithromycin (Z-Pak), and cefdinir, each used for different types of infections. Metronidazole treats certain bacterial and parasitic infections, including those in the bones, joints, and brain, and some types of meningitis and bacterial vaginosis. Unlike penicillin V, it’s not usually used for respiratory or urinary infections. Azithromycin, commonly known as a Z-Pak, is often given for pneumonia, certain sexually transmitted infections, skin infections, and throat or upper respiratory infections. It’s a good alternative for people allergic to penicillin. Cefdinir is a stronger antibiotic related to penicillin but works against more resistant bacteria. Doctors use it for more serious or recurring infections, like complicated urinary tract infections and pneumonia.

The side effects of these antibiotics are similar and may include nausea, diarrhea, vomiting, stomach pain, and rash. Severe allergic reactions, liver problems, breathing difficulties, and heart rhythm issues are also possible.

Each antibiotic has unique uses, benefits, and risks. The best way to find out which antibiotic medication, whether penicillin or another antibiotic, is best for you is to talk to a healthcare specialist.