Penicillin G (Benzylpenicillin) is a natural, beta-lactam antibiotic derived from Penicillium fungi. It is a narrow-spectrum, bactericidal antibiotic primarily effective against Gram-positive cocci, some Gram-negative cocci, and certain anaerobes. In the Indian context, it remains a first-line, cost-effective treatment for specific severe infections, particularly in secondary care settings, despite increasing resistance patterns. The 800,000 IU strength is a common parenteral dosage form.
Adult: Varies widely by infection. Example: Moderate infections: 2-4 million IU IV every 4-6 hours. Severe infections (meningitis, endocarditis): 18-24 million IU IV daily in divided doses every 4 hours. Procaine Penicillin G: 0.6-1.2 million IU IM once daily. Syphilis: Specific regimens as per stage (e.g., 2.4 million IU of Benzathine Penicillin G IM single dose for primary).
Note: For IV use: Reconstitute with Sterile Water for Injection or 0.9% Sodium Chloride. Administer by slow IV injection over 3-5 minutes or by intermittent infusion over 15-30 minutes. For IM use: Deep intramuscular injection into a large muscle mass (gluteus). Rotate sites. Procaine Penicillin G must NEVER be given IV. Always inquire about procaine allergy before administration.
Penicillin G is a bactericidal antibiotic that inhibits bacterial cell wall synthesis. It binds to and inactivates specific penicillin-binding proteins (PBPs) located on the inner membrane of the bacterial cell wall. This inactivation disrupts the final transpeptidation step of peptidoglycan synthesis, leading to the formation of a defective cell wall. The osmotic imbalance causes cell lysis and death, particularly in actively dividing bacteria.
Pregnancy: US FDA Category B. Considered generally safe and is the drug of choice for syphilis in pregnancy. Crosses the placenta. Use only if clearly needed.
Driving: Unlikely to affect ability. However, if high doses cause CNS effects like dizziness or seizures, driving should be avoided.
| Probenecid | Competitively inhibits renal tubular secretion of penicillin, increasing and prolonging serum levels. | Major |
| Methotrexate | Penicillins can reduce renal clearance of methotrexate, increasing risk of toxicity. | Major |
| Warfarin | May potentiate anticoagulant effect, increasing INR risk; mechanism may involve altered gut flora and protein binding. | Moderate |
| Oral Contraceptives | Theoretical reduced efficacy due to altered enterohepatic circulation; advise backup contraception. | Moderate |
| Aminoglycosides (e.g., Gentamicin) | Synergistic against certain organisms (e.g., Enterococci), but physical incompatibility occurs if mixed in same IV line. | Moderate |
Same composition (Penicillin G (800000IU)), different brands: