Benzathine benzylpenicillin is a long-acting form of penicillin developed to provide sustained antibacterial action after a single intramuscular injection. Created in the 1950s following the discovery of penicillin by Alexander Fleming, it was designed to release the drug slowly in the body, making it effective for treating infections such as Syphilis and preventing Rheumatic fever. Due to its long duration, low cost, and effectiveness, it remains an essential medicine recognized by the World Health Organization.
BRAND NAMES
Benzathine benzylpenicillin is an antibiotic commonly used for treating bacterial infections like syphilis and rheumatic fever prophylaxis. Bicillin L-A – commonly used in the United States.
Extencilline – available in several European countries.
Penicillin G Benzathine – often used as a generic or descriptive brand label.
Peni-LA – used in some Asian and African markets.
Benzetacil – widely known in Latin America and some European countries.
MECHANISM OF ACTION
Benzathine benzylpenicillin kills bacteria by blocking cell wall synthesis. It binds to penicillin-binding proteins, weakens the wall, and causes bacterial lysis, with its slow-release form providing prolonged effect.
PHARMACOKINETICS
Absorption
Benzathine benzylpenicillin is poorly absorbed orally, so it is administered intramuscularly. After injection, it is slowly absorbed into the bloodstream, producing low but prolonged plasma levels that can last 2–4 weeks, making it ideal for long-acting therapy or prophylaxis.
Distribution
Benzathine benzylpenicillin has a low volume of distribution (0.1–0.2 L/kg) and binds moderately to plasma proteins (55–65%). It mainly stays in the extracellular fluid, with limited penetration into the CSF and other tissues, maintaining prolonged low-level concentrations after intramuscular injection.
Metabolism
Benzathine benzylpenicillin is minimally metabolized in the body. It is slowly converted to active penicillin G after intramuscular injection, while most of its activity comes from the parent drug circulating in plasma
Excretion
Benzathine benzylpenicillin is primarily excreted unchanged by the kidneys through glomerular filtration and tubular secretion. A small amount may be broken down before excretion, but most of the drug is eliminated renally, making kidney function important for clearance.
PHARMACODYNAMICS
Benzathine benzylpenicillin is a time-dependent, bactericidal antibiotic that kills bacteria by blocking cell wall synthesis. Its slow-release form provides prolonged plasma levels, ensuring effective activity against Streptococcus and Treponema pallidum.
ADMINISTRATION
Benzathine benzylpenicillin is given by intramuscular injection only, never orally. It is usually injected into the upper outer quadrant of the gluteal muscle, providing slow, prolonged release for long-acting therapy or prophylaxis.
DOSAGE AND STRENGTH
Benzathine benzylpenicillin is available in 1.2 MU and 2.4 MU vials for intramuscular injection. Adults typically receive 2.4 MU for syphilis or1.2–2.4 MU every 3–4 weeks for rheumatic fever prophylaxis, while children receive weight-based doses up to 2.4 MU.
FOOD INTERACTIONS
Benzathine benzylpenicillin has no significant food interactions because it is given intramuscularly, bypassing the digestive system. Food does not affect its absorption or effectiveness.
DRUG INTERACTIONS
Benzathine benzylpenicillin may interact with tetracyclines, probenecid, methotrexate, and oral contraceptives, affecting its effectiveness or clearance. Patients should inform their doctor of all medications before use.
CONTRAINDICATIONS
Benzathine benzylpenicillin is contraindicated in patients with a known hypersensitivity to penicillin or other β-lactam antibiotics.
SIDE EFFECTS
Common: pain, redness, or swelling at the injection site, mild rash, fever.
Allergic reactions: urticaria, itching, angioedema.
Severe reactions: anaphylaxis, serum sickness (rare).
TOXICITY
Benzathine benzylpenicillin has low toxicity at normal doses. Overdose may cause seizures, blood disorders, kidney issues, or severe allergic reactions, which are managed with supportive care.
