benzathinepenicillin

Benzathine penicillin G is a long-acting form of penicillin G created by combining penicillin G with benzathine to form a depot that releases active drug slowly after intramuscular injection. It is a beta-lactam antibiotic and shares the mechanism of penicillin G, inhibiting bacterial cell wall synthesis by binding penicillin-binding proteins and producing bactericidal effects against susceptible organisms.

Its spectrum is mainly for certain gram-positive cocci, including many beta-hemolytic streptococci, with limited activity against Staphylococcus aureus and most gram-negative bacteria. It is not effective against beta-lactamase–producing organisms unless combined with additional agents. A notable use is for infections caused by Treponema pallidum (syphilis) and for long-term prophylaxis of rheumatic fever.

Clinical use centers on treating syphilis, with regimens varying by stage, and on primary or secondary prophylaxis of rheumatic fever. It may be employed for other streptococcal infections where a long-acting penicillin is advantageous; dosing depends on the infection and patient factors. It is administered intramuscularly and should not be given intravenously due to risk of serious adverse reactions.

Adverse effects include injection-site pain and hypersensitivity reactions, up to anaphylaxis in penicillin-allergic individuals. A Jarisch-Herxheimer reaction can occur after treatment of early syphilis. Interactions include increased penicillin levels with probenecid and potential antagonism with antibiotics that interfere with penicillin activity.

Pharmacokinetically, the drug forms a depot at the injection site, releasing penicillin G over days to weeks and maintaining therapeutic concentrations in susceptible organisms; renal clearance governs elimination.