Benzathine penicillin G is a long-acting, repository form of penicillin G, a natural penicillin antibiotic. It is a combination of one mole of penicillin G and two moles of benzathine, resulting in a very low solubility. This allows for a sustained release of penicillin G from the intramuscular injection site, providing detectable serum levels for up to 4 weeks. It is a cornerstone in public health programs in India for the prevention and treatment of specific bacterial infections, particularly group A streptococcal pharyngitis (to prevent rheumatic fever) and syphilis.
Adult: Rheumatic Fever Prophylaxis: 1,200,000 IU IM every 3-4 weeks or 2,400,000 IU IM every 4 weeks. Early Syphilis: 2,400,000 IU IM as a single dose. Strep Pharyngitis: 1,200,000 IU IM as a single dose (or 2,400,000 IU for larger adults).
Note: FOR DEEP INTRAMUSCULAR INJECTION ONLY. Use the upper outer quadrant of the gluteal region. In adults, the ventrogluteal site is preferred. Aspirate before injection to avoid intravascular administration. Administer slowly. The suspension is thick; use a 19- or 20-gauge needle. Shake the multi-dose vial vigorously before withdrawing the dose. Do not mix with other medications.
Benzathine penicillin G, after hydrolysis to penicillin G, acts as a bactericidal agent against susceptible microorganisms during active multiplication. It inhibits the third and final stage of bacterial cell wall synthesis by binding to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall. This binding inhibits the transpeptidase enzyme, preventing cross-linking of peptidoglycan chains, which is essential for cell wall strength and rigidity. The osmotic imbalance leads to cell lysis and death.
Pregnancy: US FDA Pregnancy Category B. Considered safe and is the drug of choice for treating syphilis in pregnancy to prevent congenital syphilis. Crosses the placenta. Benefits outweigh risks.
Driving: Unlikely to affect ability to drive or operate machinery. However, dizziness has been reported rarely.
| Probenecid | Markedly increases and prolongs serum penicillin levels by blocking renal tubular secretion. | Moderate |
| Methotrexate | Penicillins may reduce renal clearance of methotrexate, increasing risk of toxicity. | Major |
| Oral Contraceptives | Potential decreased efficacy of oral contraceptives; advise use of backup non-hormonal contraception. | Moderate |
| Warfarin | Possible increased anticoagulant effect; monitor INR closely. | Moderate |
| Aminoglycosides (e.g., Gentamicin) | In vitro antagonism may occur if mixed together; administer separately. | Minor |