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penicillin G potassium

Generic Pfizerpen

Used for Bacterial Infection, Pneumonia, Meningitis

Penicillin G (Pfizerpen) is an antibiotic used to treat a wide variety of bacterial infections. It's typically given as an injection or infusion in the hospital or provider's office. Since it doesn't last long in the body, it usually needs to be given multiple times a day.

Reviewed by:

Kristianne Hannemann, PharmD

Allison Gourley, PharmD

Last reviewed on April 5, 2022

Basics Side effects Pharmacist tips FAQs Warnings Dosage Interactions Alternatives Latest news Images Prices Medicare

What is Penicillin G (Pfizerpen)?

What is Penicillin G (Pfizerpen) used for?

Streptococcus and some staphylococcus infections, including pneumonia and meningitis
Anthrax
Actinomyces infections
Clostridium infections (add-on treatment), including botulism and tetanus
Diphtheria (add-on treatment)
Erysipelothrix endocarditis
Vincent's disease
Listeria infections
Pasteurella infections
Haverhill fever and rat-bite fever
Certain gonococcal infections
Syphilis
Meningococcal infections, including meningitis and sepsis
Gram-negative bacteria infections (e.g., salmonella)

How Penicillin G (Pfizerpen) works

Penicillin G (Pfizerpen) an antibiotic that kills bacteria by preventing them from making their own protective covering.

Are you looking for information on penicillin (Penicillin VK), Bicillin L-A (penicillin G benzathine) long-acting injection, or Bicillin C-R (penicillin G benzathine / penicillin G procaine) intramuscular injection instead?

Drug Facts

Common BrandsPfizerpen

Drug ClassPenicillin antibiotic

Controlled Substance ClassificationNot a controlled medication

Generic StatusLower-cost generic available

AvailabilityPrescription only

What are the side effects of Penicillin G (Pfizerpen)?

The following side effects may get better over time as your body gets used to the medication. Let your healthcare provider know immediately if you continue to experience these symptoms or if they worsen over time.

Common Side Effects

Allergic reaction (rash, itching, fever, stomach pain, muscle pain, joint pain)
Inflammation at injection site
Nausea
Vomiting
Diarrhea
Stomach pain
Sore mouth
Jarisch-Herxheimer reaction if treated for syphilis (fever, chills, nausea, vomiting, fast heartbeat)

Other Side Effects

Gut inflammation (swelling)
Muscle twitching
Kidney damage

Serious Side Effects

Contact your healthcare provider immediately if you experience any of the following.

Severe allergic reaction: hives, chest tightness, trouble breathing, swelling in your lips, tongue, or face
Clostridioides difficile (C. diff) diarrhea: loose stools, watery or bloody diarrhea, stomach pain, vomiting, fever, nausea

Source: DailyMed

The following side effects have also been reported

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Stop taking this medicine and get emergency help immediately if any of the following effects occur:

Less common

Fast or irregular breathing

fever

joint pain

lightheadedness or fainting (sudden)

puffiness or swelling around the face

red, scaly skin

shortness of breath

skin rash, hives, itching

Check with your doctor immediately if any of the following side effects occur:

Rare

Abdominal or stomach cramps and pain (severe)

abdominal tenderness

convulsions (seizures)

decreased amount of urine

diarrhea (watery and severe), which may also be bloody

mental depression

nausea and vomiting

pain at place of injection

sore throat and fever

unusual bleeding or bruising

yellow eyes or skin

Rare

For penicillin G procaine only

Agitation or combativeness

anxiety

confusion

fear of impending death

feeling, hearing, or seeing things that are not real

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

Diarrhea (mild)

headache

sore mouth or tongue

vaginal itching and discharge

white patches in the mouth and/or on the tongue

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Pharmacist tips for Penicillin G (Pfizerpen)

Make sure to finish the entire course of penicillin G (Pfizerpen) as prescribed by your provider, even if you're feeling better. Stopping antibiotics too early can cause your infection to come back or be harder to treat.

Penicillin G (Pfizerpen) is typically given as an intravenous (IV) infusion, but it can also be injected into the muscle. Your provider will decide how you should get this medication.

Penicillin G (Pfizerpen) can cause you to have an allergic reaction. These reactions can happen immediately (usually within 20 minutes after the start of treatment) or later (usually within 1 to 2 weeks after the start of treatment). Tell your provider or get medical help right away if you have a rash, itchy skin, trouble breathing, or swelling in your lips, tongue, or face after taking penicillin G (Pfizerpen).

Penicillin G (Pfizerpen) interacts with certain medications including aspirin, indomethacin (Indocin), and furosemide (Lasix). If taken together, these other medications can raise the penicillin G (Pfizerpen) levels in your body and put you at higher risk for side effects. Make sure your provider and pharmacists know all of the medications you are using.

Frequently asked questions about Penicillin G (Pfizerpen)

Can penicillin G (Pfizerpen) be given orally?

Penicillin G (Pfizerpen) is not given by mouth. This form of penicillin breaks down too easily in the stomach, so it doesn't absorb in your body very well. Another form of penicillin, penicillin V potassium, absorbs better and is available as a tablet and oral solution. However, it might not work as well for more serious infections.

Is penicillin G (Pfizerpen) long acting?

Penicillin G (Pfizerpen) doesn't last long in the body. Most people who take this medication need many IV infusions or IM injections each day, or even an all-day infusion. The names look very similar, but this medication is different from the long-acting penicillin shots. Bicillin C-R (penicillin G benzathine / penicillin G procaine) a few days and Bicillin L-A (penicillin G benzathine) lasts over a week.

Is penicillin G (Pfizerpen) safe to use during pregnancy?

There isn't enough information to know if penicillin G (Pfizerpen) is safe to use during pregnancy. In animal studies, penicillin G (Pfizerpen) didn't cause harm to unborn babies. There also doesn't appear to be any harm to unborn human babies. Speak to your provider about the risks and benefits of penicillin G (Pfizerpen) for you and your unborn baby if you're pregnant.

How long will I need to take penicillin G (Pfizerpen)?

Your provider will determine how long you'll need to take penicillin G (Pfizerpen) based on your type of infection and how serious it is. In general, penicillin G (Pfizerpen) is typically used for at least 48 to 72 hours after your symptoms are gone. If you are being treated for streptococcal infection, you'll need to take the medication for at least 10 days. Make sure to follow your provider's instructions on how long you need to take this medication, and don't stop early because this puts you at risk for your infection coming back and becoming harder to treat.

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What are the risks and warnings for Penicillin G (Pfizerpen)?

Penicillin G (Pfizerpen) can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options.

Allergic reaction

Risk factors: History of allergy to penicillin or cephalosporin antibiotics | History of asthma

Penicillin G (Pfizerpen) can cause allergic reactions that can be deadly. If you've had an allergy to any penicillin or cephalosporin antibiotic in the past, tell your provider before taking penicillin G (Pfizerpen). Get medical help right away if you experience trouble breathing, chest tightness, or swelling of your lips, tongue, or face.

Clostridioides difficile (C. diff) diarrhea

Risk factors: Long-term use of antibiotics | Taking other antibiotics

Sometimes antibiotics including penicillin G (Pfizerpen) can lead to a new infection caused by too much C. difficile bacteria growing in your gut. This infection can cause serious diarrhea that can be life-threatening, and it's important you get treated with different antibiotics. If you experience fever, stomach cramps, or diarrhea, even after you stop taking penicillin G (Pfizerpen), let your provider know right away.

New infections

Risk factors: Intravenous (IV) catheter

Penicillin G (Pfizerpen) can kill good bacteria in your body and promote the growth of other bacteria or fungi. This can lead to new infections. You're at a higher risk if you have an IV catheter (a tube inserted in your vein so you can get IV medications). Tell your provider if you have a fever, muscle pain, chills, or feel unwell while taking penicillin G (Pfizerpen) so you can be checked and treated for any new infections that happen.

Penicillin G (Pfizerpen) dosage forms

Typical dosing for Penicillin G (Pfizerpen)

Penicillin G (Pfizerpen) is usually given as an intravenous (IV) or intramuscular (IM) injection in a hospital setting or at home by a healthcare provider. Your provider will make sure you get this medication at the correct dose and time.

The dose depends on the condition being treated. In children, the dose will also depend on their weight.

Interactions between Penicillin G (Pfizerpen) and other drugs

Penicillin G (Pfizerpen) may interact with certain medications or supplements. Always let your doctor and pharmacist know about any other medications or supplements (including prescribed and over-the-counter medications, vitamins, and dietary or herbal supplements) that you are currently taking. The list below does not include all possible drug interactions with Penicillin G (Pfizerpen). Please note that only the generic name of each medication is listed below.

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking any of these medicines, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using medicines in this class with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.