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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Other
Penicillin G Benzathine is a long-acting, injectable antibiotic used to treat bacterial infections like syphilis and prevent rheumatic fever. It belongs to the natural penicillin class of medications.
Name
Penicillin G Benzathine
Raw Name
PENICILLIN G BENZATHINE
Category
Other
Drug Count
4
Variant Count
8
Last Verified
February 17, 2026
RxCUI
2671687, 2684991, 731538, 731541, 731564, 731566, 731567, 731568, 731570, 731571, 836306, 836307
UNII
RIT82F58GK, 17R794ESYN
About Penicillin G Benzathine
Penicillin G Benzathine is a long-acting, injectable antibiotic used to treat bacterial infections like syphilis and prevent rheumatic fever. It belongs to the natural penicillin class of medications.
Detailed information about Penicillin G Benzathine
References used for this content
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Penicillin G Benzathine.
Penicillin G Benzathine is a long-acting, repository form of penicillin, an antibiotic that has remained a cornerstone of infectious disease management since its introduction. It is a salt form of Penicillin G, specifically designed for deep intramuscular (IM) injection. Unlike immediate-release antibiotics, Penicillin G Benzathine is formulated to release the active drug slowly into the bloodstream over a period of weeks, providing sustained therapeutic levels that are essential for treating certain chronic or slow-growing infections. It belongs to the class of drugs known as natural penicillins (beta-lactams).
Historically, the FDA first approved Penicillin G Benzathine in the early 1950s (marketed as Bicillin L-A), and it remains the gold standard treatment for various stages of syphilis. Because it is an injectable 'depot' formulation, it is particularly valuable in public health settings where patient compliance with multiple daily oral doses of antibiotics might be a concern. It is important to note that this specific formulation is exclusively for intramuscular use; intravenous (IV) administration is strictly prohibited due to the risk of severe, life-threatening complications. Healthcare providers typically use this medication to target specific Gram-positive bacteria, most notably Streptococcus pyogenes and Treponema pallidum.
At the molecular level, Penicillin G Benzathine is a bactericidal agent, meaning it kills bacteria rather than just inhibiting their growth. It achieves this by interfering with the synthesis of the bacterial cell wall. Bacteria require a rigid cell wall to maintain their structural integrity and survive the osmotic pressure of their environment. This wall is primarily composed of a complex polymer called peptidoglycan.
Penicillin G Benzathine targets and binds to specific proteins on the inner surface of the bacterial cell membrane known as Penicillin-Binding Proteins (PBPs). These PBPs are enzymes (specifically transpeptidases) responsible for the final stages of cross-linking the peptidoglycan chains. When Penicillin G Benzathine binds to these enzymes, it inhibits their activity, preventing the formation of a stable cell wall. This leads to the development of weak spots in the wall, eventually causing the bacterial cell to burst (lysis) and die. Because human cells do not have cell walls or peptidoglycan, the drug specifically targets bacterial cells with minimal direct toxicity to human tissues, though allergic reactions remain a significant clinical concern.
According to the FDA-approved labeling and CDC treatment guidelines, Penicillin G Benzathine is indicated for:
Penicillin G Benzathine is available exclusively as an injectable suspension. It is most commonly found in pre-filled syringes for convenience and to ensure sterile administration. Common strengths include:
It is often marketed under the brand name Bicillin L-A. It is critical to distinguish this from Bicillin C-R, which contains a mixture of benzathine and procaine salts and is not appropriate for treating syphilis.
> Important: Only your healthcare provider can determine if Penicillin G Benzathine is right for your specific condition. This medication must be administered by a healthcare professional in a clinical setting.
Dosage of Penicillin G Benzathine is highly dependent on the specific infection being treated and the patient's history. According to the CDC Sexually Transmitted Infections Treatment Guidelines (2021):
Penicillin G Benzathine is approved for use in children, with dosages typically adjusted based on body weight:
In patients with severe renal (kidney) impairment (Creatinine Clearance < 10 mL/min), the rate of excretion is significantly reduced. While the slow-release nature of benzathine penicillin provides a buffer, healthcare providers may consider extending the interval between doses or reducing the total dose to prevent accumulation and neurotoxicity.
No specific dosage adjustments are typically required for patients with isolated hepatic (liver) impairment, as the drug is primarily cleared by the kidneys.
Geriatric patients often have naturally declining renal function. Healthcare providers should monitor kidney function and may adjust the dosage frequency accordingly. There is an increased risk of sodium accumulation if high doses are used in patients with heart failure.
Penicillin G Benzathine is never taken by mouth. It must be administered via deep intramuscular (IM) injection by a trained healthcare professional. The following protocols are standard:
Because this medication is administered by a healthcare professional, a missed dose usually involves a missed appointment. If you miss a scheduled injection for syphilis or rheumatic fever prophylaxis, contact your clinic immediately. For syphilis, if more than 7-9 days pass between doses in a multi-dose series, the entire series may need to be restarted to ensure efficacy.
An overdose of Penicillin G Benzathine is rare because it is administered by professionals. However, excessive levels of penicillin can lead to neuromuscular hyperexcitability or seizures. If an accidental intravenous injection occurs, it can cause 'Hoigne’s Syndrome' (pseudo-anaphylaxis) or 'Nicolau Syndrome' (tissue necrosis). Emergency measures include supportive care and monitoring of neurological and cardiac function.
> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose or skip scheduled injections without medical guidance.
The most frequently reported side effects of Penicillin G Benzathine are related to the injection itself. Because the volume of the injection is large and the suspension is thick, patients often experience:
> Warning: Stop taking Penicillin G Benzathine and call your doctor immediately if you experience any of these.
Since Penicillin G Benzathine is often used for short courses (syphilis) or infrequent intervals (rheumatic fever), long-term side effects are rare. However, repeated injections can lead to:
There have been reports of inadvertent intravenous administration of Penicillin G Benzathine which has been associated with cardiorespiratory arrest and death. Prior to administration of this drug, carefully read the labeling for 'Dosage and Administration' and 'Warnings' sections. This medication must be administered by deep intramuscular injection only.
Report any unusual symptoms to your healthcare provider.
Penicillin G Benzathine is a potent antibiotic that must be used with extreme caution. The most critical safety factor is the route of administration. It is a thick, milky suspension that is intended to stay in the muscle and release slowly. If it enters the bloodstream directly (via a vein or artery), it can cause catastrophic vascular occlusion (blockage) and organ damage.
FDA Black Box Warning (Summary): Penicillin G Benzathine is strictly for INTRAMUSCULAR USE ONLY. Inadvertent intravenous (IV) administration has resulted in cardiac arrest, permanent neurological damage, gangrene requiring amputation, and death. Healthcare providers must aspirate before injection to ensure a blood vessel has not been entered. It should not be mixed with other IV fluids or medications.
Penicillin G Benzathine generally does not interfere with the ability to drive or operate machinery. However, if a patient experiences dizziness or the fear/anxiety associated with Hoigne’s Syndrome immediately following an injection, they should wait until symptoms resolve before driving.
There is no direct chemical interaction between alcohol and Penicillin G Benzathine. However, alcohol can weaken the immune system and may exacerbate some side effects like nausea or headache. It is generally advised to avoid excessive alcohol consumption while the body is fighting a serious infection like syphilis.
In the context of syphilis, 'discontinuation' usually means failing to complete the 3-dose series for late latent cases. This is dangerous as it may lead to treatment failure and progression to tertiary syphilis (which can affect the brain and heart). If a patient develops a severe allergic reaction, the drug must be discontinued immediately, and alternative antibiotics (like doxycycline) may be considered.
> Important: Discuss all your medical conditions with your healthcare provider before starting Penicillin G Benzathine.
Since Penicillin G Benzathine is administered via injection, food does not affect its absorption. There are no specific restrictions regarding dairy, grapefruit, or high-fat meals. However, maintaining a healthy diet is recommended to support immune function during infection recovery.
For each major interaction, the management strategy usually involves dose adjustment of the non-antibiotic drug or increased clinical monitoring of the patient's symptoms and lab values.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking.
Penicillin G Benzathine must NEVER be used in the following circumstances:
These conditions require a careful risk-benefit analysis by the healthcare provider:
Patients should be aware that if they are allergic to Penicillin G Benzathine, they are likely also allergic to:
> Important: Your healthcare provider will evaluate your complete medical history before prescribing Penicillin G Benzathine. Always wear a medical alert bracelet if you have a confirmed penicillin allergy.
FDA Pregnancy Category B: Penicillin G Benzathine is generally considered safe for use during pregnancy. It has been used for decades to treat syphilis in pregnant women, which is a critical intervention to prevent congenital syphilis in the newborn.
Penicillin G is excreted in human breast milk in small amounts.
Penicillin G Benzathine is FDA-approved for use in infants and children for the treatment of syphilis and streptococcal infections.
In patients with a GFR (Glomerular Filtration Rate) below 30 mL/min, the excretion of Penicillin G is delayed. While the benzathine form is already slow-release, clinicians should monitor for signs of 'penicillin encephalopathy' (confusion, jerking movements) if repeated doses are given to patients with kidney failure.
No major adjustments are needed for patients with liver disease, as the liver plays a minimal role in the clearance of this drug. However, if a patient has both liver and kidney failure, the risk of toxicity increases significantly.
> Important: Special populations require individualized medical assessment and close monitoring by a specialist.
Penicillin G Benzathine exerts its bactericidal effect by inhibiting the biosynthesis of the bacterial cell wall. The target is the peptidoglycan layer, which provides structural strength to the cell. The drug binds to Penicillin-Binding Proteins (PBPs), which are transpeptidase enzymes. By acylating these enzymes, the drug prevents the cross-linking of the peptidoglycan side chains. This inhibition triggers the release of bacterial autolytic enzymes (autolysins), which further degrade the cell wall, leading to osmotic lysis and cell death.
| Parameter | Value |
|---|---|
| Bioavailability | 100% (Intramuscular) |
| Protein Binding | 60% (Mainly Albumin) |
| Half-life (Effective) | 1–4 weeks (due to depot release) |
| Tmax | 12–24 hours (initial peak) |
| Metabolism | Minimal (Hydrolysis of salt) |
| Excretion | Renal (primarily unchanged) |
Penicillin G Benzathine is classified as a Natural Penicillin within the broader category of Beta-Lactam Antibiotics. It is distinguished from 'Aminopenicillins' (like Amoxicillin) by its narrower spectrum and from 'Antistaphylococcal Penicillins' (like Nafcillin) by its susceptibility to penicillinase enzymes produced by many Staphylococcus species.
Medications containing this ingredient
Common questions about Penicillin G Benzathine
Penicillin G Benzathine is primarily used to treat syphilis at various stages, including primary, secondary, and latent syphilis. It is also a standard treatment for Group A streptococcal infections, such as strep throat, especially when a patient cannot complete a 10-day oral antibiotic course. Additionally, it is used as a long-term preventative measure (prophylaxis) for patients who have had rheumatic fever to prevent recurrent attacks that could damage the heart. In some parts of the world, it is also used to treat other treponemal diseases like yaws and pinta. Because it stays in the system for a long time, it is ideal for infections that require sustained antibiotic levels.
The most common side effects are related to the injection site, as the medication is a thick suspension that requires a large needle. Patients frequently report significant pain, redness, and swelling at the site of the injection in the buttock or thigh. Some people may also develop a small, hard lump under the skin called an induration, which can take several days to disappear. General side effects like a mild headache, nausea, or a low-grade fever can also occur shortly after administration. While these are usually manageable, any signs of a rash or difficulty breathing should be reported to a doctor immediately.
There is no known direct chemical interaction between alcohol and Penicillin G Benzathine that would cause a dangerous reaction. However, healthcare providers generally recommend avoiding alcohol while being treated for a serious infection like syphilis, as alcohol can dehydrate the body and suppress the immune system. Alcohol may also worsen some of the minor side effects of the medication, such as dizziness or nausea. If you are being treated for a sexually transmitted infection, it is best to focus on rest and hydration to allow the antibiotic to work effectively. Always consult your doctor for specific advice regarding your lifestyle during treatment.
Yes, Penicillin G Benzathine is considered safe and is actually the preferred treatment for syphilis during pregnancy. It is classified as Pregnancy Category B, meaning animal studies have shown no risk and there is no evidence of harm in human pregnancies. Treating syphilis in a pregnant woman is vital because the infection can be passed to the fetus, leading to severe complications or stillbirth. If a pregnant woman is allergic to penicillin, doctors usually recommend a process called desensitization so she can safely receive the drug. It is one of the most well-studied and essential medications for maternal-fetal health.
Penicillin G Benzathine begins working shortly after the injection as the drug starts to slowly leach into the bloodstream, but its effects are designed to be gradual. For an infection like strep throat, symptoms may begin to improve within 24 to 48 hours. However, for syphilis, the 'work' of the drug involves killing the bacteria over a period of weeks, and you may not 'feel' a difference immediately. In fact, some patients feel worse initially due to the Jarisch-Herxheimer reaction. It is important to remember that even if you feel better, the drug continues to work in your body for up to 30 days after a single injection.
Since Penicillin G Benzathine is usually given as a single injection or a series of three weekly injections by a healthcare professional, you cannot 'stop' it in the traditional sense once it is injected. The medication is a depot formulation, meaning it stays in your muscle and releases slowly over several weeks. If you are scheduled for a series of three shots and decide to skip the remaining ones, the treatment may fail, and the infection could return or progress. If you experience a severe side effect, your doctor will not give you further injections and will switch you to a different class of antibiotics. Always complete the full course as directed by your clinic.
If you miss a scheduled appointment for a Penicillin G Benzathine injection, you should contact your healthcare provider or clinic immediately to reschedule. This is especially critical when treating late latent syphilis, where three weekly doses are required. CDC guidelines suggest that if the interval between doses exceeds 7 to 9 days, the entire treatment series may need to be restarted from the beginning to ensure the bacteria are fully eradicated. Missing a dose for rheumatic fever prophylaxis also puts you at risk for a recurrent attack. Timely administration is key to the success of this long-acting antibiotic.
There is no clinical evidence to suggest that Penicillin G Benzathine causes weight gain. Unlike some medications like steroids or certain antidepressants, antibiotics do not typically interfere with metabolism or appetite in a way that leads to fat accumulation. If you notice sudden weight gain or swelling (edema) after an injection, you should contact your doctor, as this could be a sign of a rare allergic reaction or a kidney issue rather than typical weight gain. Most patients do not experience any changes in their weight during a standard course of this antibiotic.
Penicillin G Benzathine can interact with several other medications, so it is vital to disclose your full medication list to your doctor. It can interfere with the clearance of methotrexate (a drug for cancer and rheumatoid arthritis), potentially leading to toxicity. It may also reduce the effectiveness of live vaccines like the oral typhoid vaccine. Some studies suggest a minor interaction with birth control pills, though this is debated. Probenecid, a gout medication, can cause penicillin levels to stay higher for longer. Your doctor will review these interactions to ensure your treatment plan is safe and effective.
Penicillin G Benzathine is available as a brand-name product, most notably Bicillin L-A, and while the term 'generic' is often used, the manufacturing of this specific complex suspension is difficult. In many regions, there are very few manufacturers of the benzathine salt formulation, which has led to global shortages in recent years. It is an older drug, so it is not protected by modern patents, but the specialized nature of its 'depot' delivery system means you will usually receive the Bicillin L-A brand. Always ensure the clinic is using the 'L-A' (Long-Acting) version and not 'C-R' (Combination) if you are being treated for syphilis.