Penicillin G Benzathine

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Cat Number

API0232893

CAS Number

41372-02-5

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Product Detail Description Scientific Support Customer Q&A

CAS Number

41372-02-5

EINECS

804-898-2

Storage

Store in tight containers

Synonyms

Benzathine Penicillin; Benzathine Benzylpenicillin

Molecular Formula

C48H64N6O12S2

Molecular Weight

981.2

Smiles

CC1([C@@H](N2[C@H](S1)[C@@H](C2=O)NC(=O)CC3=CC=CC=C3)C(=O)O)C.CC1([C@@H](N2[C@H](S1)[C@@H](C2=O)NC(=O)CC3=CC=CC=C3)C(=O)O)C.C1=CC=C(C=C1)CNCCNCC2=CC=CC=C2.O.O.O.O

Appearance

White crystalline powder

Melting Point

123-124℃

Boiling Point

663.3℃

General Description

Penicillin G benzathine is the benzathine salt form of natural penicillin G, formulated as a sterile aqueous suspension for deep intramuscular injection only. Due to its extremely low solubility and slow absorption, it is classified as a prescription antibiotic against intravenous administration.

Mechanism of Action

Penicillin G exerts bactericidal activity by inhibiting bacterial cell wall peptidoglycan synthesis during active multiplication, binding to penicillin-binding proteins and disrupting transpeptidation. The benzathine salt form undergoes slow hydrolysis at the injection site, releasing penicillin G into the circulation and producing prolonged but low serum concentrations.

Application

Penicillin G benzathine is indicated for treatment of group A streptococcal upper respiratory infections and for syphilis of all stages including primary, secondary, and latent disease. It serves as the gold standard for rheumatic fever prophylaxis with monthly intramuscular injections and is also used for yaws, bejel, and pinta.

Ubals M, et al. compared oral linezolid (600 mg daily for 5 days) with intramuscular benzathine penicillin G (single 2.4 million unit dose) for the treatment of early syphilis. Among 59 participants with primary, secondary, or early latent syphilis, treatment response rates at 48 weeks were 70% in the linezolid group versus 100% in the penicillin group (treatment difference –29.6%; 95% CI –50.5 to –8.8), failing to meet the noninferiority criterion. Adverse event rates were similar between groups, and no serious events were reported.

Fig. 1 Trial profile An interim futility analysis was done when 50 participants reached the 24-week follow-up. (Ubals M, et al., 2024)

References

Ubals M, et al. Oral linezolid compared with benzathine penicillin G for treatment of early syphilis in adults (Trep-AB Study) in Spain: a prospective, open-label, non-inferiority, randomised controlled trial. Lancet Infect Dis. 2024;24(4):404-416.

Does Penicillin G Benzathine require refrigerated storage to maintain stability?

Yes, it must be stored at 2-8°C. As a penicillin derivative, it is susceptible to hydrolysis at room temperature, leading to rapid loss of potency and increased impurities.

Is Penicillin G Benzathine more stable than other penicillin salts?

The benzathine salt form provides enhanced stability and prolonged release compared to potassium or sodium salts, but it still requires strict temperature control to prevent degradation.

What is the recommended humidity level for storing Penicillin G Benzathine?

It should be stored in a low-humidity environment (below 50% RH). Moisture absorption can trigger hydrolysis of the beta-lactam ring, rendering the antibiotic ineffective.

How is the particle size of Penicillin G Benzathine controlled for injectable suspensions?

We use laser diffraction to ensure tight particle size distribution, as uniformity is critical for syringeability and consistent pharmacokinetics of the long-acting suspension.