benzathine

Benzathine is an organic amine that is best known in medicine as the bulky base component used to form long-acting penicillin formulations. The compound itself has little direct antimicrobial activity; its clinical value lies in its ability to create depot salts with penicillin G that release the active antibiotic slowly after intramuscular injection.

In clinical practice, benzathine is encountered most often as benzathine penicillin G, a long-acting preparation used to treat certain infections and to provide extended penicillin exposure. When administered by intramuscular injection, the benzathine moiety slows the release of penicillin G, producing sustained plasma levels over days to weeks. This property supports less frequent dosing compared with immediate-release penicillin forms.

Common indications include the treatment of syphilis (where benzathine penicillin G is preferred for certain stages) and prophylaxis against rheumatic fever and some streptococcal infections in selected patients, depending on local guidelines and allergies. The choice of benzathine-containing formulations reflects a balance between achieving adequate antimicrobial exposure and patient adherence.

Pharmacologically, benzathine serves as a depot carrier rather than as the antimicrobial agent itself. The activity against bacteria derives from penicillin G released from the salt, not from benzathine per se. Safety considerations align with those of penicillin therapies: potential hypersensitivity reactions, injection-site reactions, and, in the treatment of syphilis, possible Jarisch–Herxheimer reactions. Benzathine-containing products should be avoided in individuals with known penicillin allergies.

See also: penicillin, penicillin G, long-acting penicillins.