Penicillin G (Benzylpenicillin)
Pronunciation: (pen-ih-SILL-in jee).
- Generic name
- Penicillin G (benzylpenicillin)
- Brand names
- Benacillin, Penicillin G Sodium, BenPen, Penlong, Penicillin G Potassium, Penidure
- Drug class
- Antibiotic (Natural Penicillin)
Availability and supply rules vary by country
Trade names by country: United States · Canada
Australia: · Full directory
What Penicillin G (benzylpenicillin) is and how it works
Uses, formulations, monitoring, and supply rules can differ by patient, product, and country. Follow the exact local product information and professional advice.
Mechanism of action: how Penicillin G (benzylpenicillin) works
Penicillin G inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), which are essential for peptidoglycan cross-linking. This leads to cell lysis and death in susceptible bacteria. It is bactericidal and most effective against actively dividing Gram-positive organisms and some Gram-negative cocci. (1)
What Penicillin G (benzylpenicillin) is used for
Streptococcal infections (e.g., pharyngitis, scarlet fever)
Streptococcal infections (e.g., pharyngitis, scarlet fever)
Syphilis
Syphilis
Meningitis (bacterial)
Meningitis (bacterial)
Pneumonia (pneumococcal)
Pneumonia (pneumococcal)
Diphtheria
Diphtheria
Before taking Penicillin G (benzylpenicillin)
Do not take / not appropriate for
- Contraindicated in patients with known hypersensitivity to penicillins. (Contraindication)
Tell your clinician about
How to take Penicillin G (benzylpenicillin)
- General Instructions: Penicillin G is administered by a healthcare professional, usually as an intravenous (IV) or intramuscular (IM) injection. Follow your healthcare provider's instructions closely.. Adult Dosing: Typical adult doses range from 1 to 5 million units every 4–6 hours, depending on the severity and type of infection. Dosage may be higher for severe infections like meningitis or endocarditis.. Pediatric Dosing: Children's doses are based on weight and infection type. For example, neonates may receive 50,000 units/kg every 8–12 hours; older children may require 100,000–250,000 units/kg/day divided every 4–6 hours.. Administration: Given by injection into a vein or muscle. Do not self-administer unless instructed and trained by a healthcare professional.. When To Stop: Complete the full prescribed course, even if symptoms improve. Do not stop early unless directed by your doctor.. Storage: Store powder for solution at room temperature. Reconstituted solutions should be used promptly or stored as directed by the pharmacist or product label.
- This page does not provide a dose calculator. Dosing must follow the prescriber, pharmacist, or product label.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician.
Missed dose
If you miss a dose, contact your healthcare provider immediately for instructions. Do not double the next dose to make up for a missed one.
Overdose
Symptoms of overdose may include muscle twitching, seizures, confusion, or kidney dysfunction. Seek emergency medical attention or call your local poison control center immediately.
Side effects
Side effects and their urgency vary; report severe, persistent, or concerning symptoms to a healthcare professional.
Diarrhea
Incidence: Reported in the clinician-authored database; frequency not established
Nausea
Incidence: Reported in the clinician-authored database; frequency not established
Vomiting
Incidence: Reported in the clinician-authored database; frequency not established
Rash
Incidence: Reported in the clinician-authored database; frequency not established
Hives
Incidence: Reported in the clinician-authored database; frequency not established
Allergic reaction (anaphylaxis)
Incidence: Reported in the clinician-authored database; frequency not established
Seizures
Incidence: Reported in the clinician-authored database; frequency not established
Kidney problems
Incidence: Reported in the clinician-authored database; frequency not established
Serious warnings
Serious allergic reactions can occur, including anaphylaxis — serious
Symptoms: Serious allergic reactions can occur, including anaphylaxis. May cause Clostridioides difficile-associated diarrhea. Dose adjustment is needed in renal impairment. Monitor for signs of superinfection with prolonged use. Use caution in patients with a history of seizures.
Action: Follow the urgency stated and seek prompt or emergency care when indicated.
Contraindications recorded in the clinician database — serious
Symptoms: Contraindications recorded in the clinician database: Contraindicated in patients with known hypersensitivity to penicillins. Use with caution in patients with renal impairment, seizure disorders, or a history of severe allergies. Monitor for signs of superinfection, especially with prolonged therapy.
Action: Follow the urgency stated and seek prompt or emergency care when indicated.
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Recorded interactions | Penicillin G may interact with other medications such as methotrexate (increased toxicity), oral contraceptives (reduced effectiveness), and certain anticoagulants (altered bleeding risk). Probenecid can increase blood levels of Penicillin G. Always inform your healthcare provider about all medicines and supplements you are taking. | (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy
The FDA-approved Pfizerpen (penicillin G potassium) prescribing information states this drug should be used during pregnancy only if clearly needed; this is a decision for the prescribing clinician, weighing potential benefit against potential risk.
Breastfeeding
Neither the clinician-authored database content nor the FDA label reviewed for this page establishes specific breastfeeding dosing guidance for penicillin G; discuss use of this medicine with your healthcare provider while breastfeeding.
Children
Frequency: Every 6-8 hours.. Weight Based: 100,000-200,000 units/kg/day in divided doses.. Max Daily Dose: Up to 300,000 units/kg/day.. Max Single Dose: Up to 300,000 units for severe infections.. Age Restrictions: Safety not established in children under 2 years.
Renal_impairment
Renal impairment: the FDA-approved label directs the prescriber to reduce the maintenance interval according to kidney function after a full loading dose — for creatinine clearance above 10 mL/min/1.73m2, one-half the loading dose is given every 4-5 hours; for creatinine clearance below 10 mL/min/1.73m2, one-half the loading dose is given every 8-10 hours. This adjustment matters because penicillin G is largely cleared by the kidneys, and very high doses can accumulate in renal impairment and cause neurotoxicity (twitching, seizures). Hepatic impairment: the label notes that additional dosage modification should be made when hepatic disease accompanies renal impairment, but does not give a separate numeric hepatic-only adjustment.
Hepatic_impairment
Renal impairment: the FDA-approved label directs the prescriber to reduce the maintenance interval according to kidney function after a full loading dose — for creatinine clearance above 10 mL/min/1.73m2, one-half the loading dose is given every 4-5 hours; for creatinine clearance below 10 mL/min/1.73m2, one-half the loading dose is given every 8-10 hours. This adjustment matters because penicillin G is largely cleared by the kidneys, and very high doses can accumulate in renal impairment and cause neurotoxicity (twitching, seizures). Hepatic impairment: the label notes that additional dosage modification should be made when hepatic disease accompanies renal impairment, but does not give a separate numeric hepatic-only adjustment.
Monitoring
Storage
The FDA-approved Pfizerpen (penicillin G potassium) prescribing information specifies storing the dry powder below 86°F (30°C). Once reconstituted into solution, it should be stored in a refrigerator and used within 7 days.
Study the drug class: Penicillins
Professional information
Clinician-facing context only. This section does not replace current product labeling.
General
Indication: Streptococcal infections (e.g., pharyngitis, scarlet fever)
Dose summary: Penicillin G: 10-20 million units/day administered in divided doses for streptococcal infections; dosing is individualized to the type and severity of infection under the FDA label.
Renal context: The FDA-approved Pfizerpen (penicillin G potassium) label sets the maintenance interval by kidney function after a full loading dose: for creatinine clearance above 10 mL/min/1.73m2, give one-half the loading dose every 4-5 hours; for creatinine clearance below 10 mL/min/1.73m2, give one-half the loading dose every 8-10 hours. This matters because penicillin G is largely renally cleared, and very high (massive) intravenous doses in impaired renal function have been linked to neurotoxic reactions including hyperreflexia, myoclonic twitching, seizures, and coma. Additional adjustment is directed when hepatic disease accompanies renal impairment, though no separate hepatic-only numeric adjustment is specified. (1)
Frequently asked questions
What infections does Penicillin G treat?
Penicillin G is used to treat serious bacterial infections such as pneumonia, meningitis, endocarditis, syphilis, and infections of the skin, blood, and joints caused by susceptible bacteria.
How is Penicillin G administered?
Penicillin G is given by injection, either into a vein (IV) or muscle (IM), usually by a healthcare professional.
What should I do if I have a penicillin allergy?
Do not take Penicillin G if you have a known allergy to penicillins. Inform your healthcare provider about any previous allergic reactions to antibiotics.
Can Penicillin G be used during pregnancy or breastfeeding?
Penicillin G is generally considered safe during pregnancy and breastfeeding, but always consult your doctor before use.
What are the signs of a serious reaction to Penicillin G?
Serious reactions include difficulty breathing, swelling of the face or throat, severe rash, or persistent diarrhea. Seek emergency medical help if these occur.
Does Penicillin G interact with other medications?
Yes, it can interact with methotrexate, oral contraceptives, anticoagulants, and probenecid. Always inform your doctor of all medications you are taking.
What should I do if I miss a dose?
Contact your healthcare provider for instructions. Do not double the next dose to make up for a missed one.
What happens if I take too much Penicillin G?
Taking too much Penicillin G can lead to symptoms such as nausea, vomiting, diarrhea, and in severe cases, neurological effects like seizures. If you suspect an overdose, it is crucial to seek immediate medical attention or contact emergency services. Do not attempt to induce vomiting or self-treat, as prompt professional evaluation is necessary.
Can I drink alcohol while taking Penicillin G?
While there is no direct contraindication for consuming alcohol with Penicillin G, it is generally advisable to limit or avoid alcohol during antibiotic treatment. Alcohol can potentially worsen common side effects like nausea or stomach upset. Additionally, alcohol consumption may impair your body's ability to fight infection and could prolong recovery.
Is Penicillin G safe during pregnancy?
Penicillin G is generally considered safe during pregnancy; however, it is classified under a category that requires careful consideration. It is imperative to consult your doctor if you are pregnant or planning to become pregnant before taking Penicillin G. Your healthcare provider will assess the benefits versus potential risks to determine the most appropriate treatment for your specific situation.
What is the mechanism of action of Penicillin G (benzylpenicillin)?
Penicillin G inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), which are essential for peptidoglycan cross-linking. This leads to cell lysis and death in susceptible bacteria. It is bactericidal and most effective against actively dividing Gram-positive organisms and some Gram-negative cocci. (1)
What is the generic name of Penicillin G (Benzylpenicillin)?
The generic name is Penicillin G (benzylpenicillin). It is sold under brand names including Benacillin, Penicillin G Sodium, BenPen, Penlong, Penicillin G Potassium, Penidure.
What class of drug is Penicillin G (benzylpenicillin)?
Penicillin G (Benzylpenicillin) is classed as: Antibiotic (Natural Penicillin).
References
- Penicillin G — Prescribing InformationMedGuideGlobal · Global · accessed 2026-08-07 · source 1
- PENICILLIN G POTASSIUM (PENICILLIN G) INJECTION, SOLUTION [BAXTER HEALTHCARE CORPORATION] — US prescribing information (DailyMed SPL)U.S. National Library of Medicine (DailyMed) · US · accessed 2026-08-14 · source 2
- Penicillin G Benzathine and Penicillin G Procaine Injection — patient drug information (MedlinePlus)U.S. National Library of Medicine (MedlinePlus) · US · accessed 2026-08-14 · source 3
- BICILLIN L-A — FDA approval record (Drugs@FDA NDA050141)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 4
- Penicillin G — RxNorm normalized drug concept (RXCUI 7980)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 5
Brand names by country
Single-ingredient Penicillin G (benzylpenicillin) names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- Pfizerpen5000000 [iU], 20000000 [iU] · roerig
- BUFFERED PENICILLIN G POTASSIUM5000000 [iU] · hf acquisition co llc, dba healthfirst
Canada
- CRYSTAPEN