What Is Lentocilin? Uses, Dosage, and What You Need to Know in 2026

Lentocilin is a brand name for benzathine benzylpenicillin (penicillin G benzathine) — a long-acting injectable antibiotic used to treat several serious bacterial infections, including syphilis, and to prevent rheumatic fever. It is manufactured in Portugal by Laboratórios Atral S.A. and is currently being imported into the United States by Mark Cuban's Cost Plus Drug Company under FDA authorization to address a critical shortage of the U.S. equivalent, Bicillin L-A.

This comprehensive guide covers what Lentocilin is, what it treats, how it's given, dosages, and what makes it unique compared to other antibiotics.

What Is Lentocilin?

Lentocilin belongs to the

natural penicillin class of antibiotics — one of the oldest and most effective antibiotic classes in medicine. The "benzathine" component is not the antibiotic itself but a slow-release salt that keeps penicillin slowly releasing into the bloodstream for up to 2-4 weeks after a single injection. This unique long-acting property makes it ideal for treating infections like syphilis, which require sustained antibiotic exposure.

Key facts about Lentocilin:

Active ingredient: Penicillin G benzathine (benzathine benzylpenicillin tetrahydrate)

Drug class: Natural penicillin (beta-lactam antibiotic)

Manufacturer: Laboratórios Atral S.A. (Portugal)

FDA status: Not FDA-approved; temporarily imported under FDA enforcement discretion

Controlled substance: No — not a DEA scheduled substance

Dosage form: Powder for reconstitution; administered as deep intramuscular injection only

What Is Lentocilin Used to Treat?

Lentocilin is indicated for treatment and prevention of infections caused by bacteria susceptible to penicillin. Its primary uses are:

Syphilis — The Most Critical Use

Lentocilin (penicillin G benzathine) is the

only first-line recommended treatment for syphilis at all stages, and the ONLY safe treatment for syphilis during pregnancy. It is used for:

Primary syphilis (initial sore/chancre stage)

Secondary syphilis (rash and systemic symptoms)

Early latent syphilis (no symptoms but infection within 1 year)

Late latent syphilis (no symptoms, infection >1 year or unknown duration)

Tertiary syphilis (adults) — advanced disease affecting organs

Congenital syphilis (newborns infected from mother)

Other Bacterial Infections

Group A streptococcal upper respiratory infections (strep throat — though oral antibiotics are preferred to conserve supply)

Rheumatic fever prophylaxis (monthly injections to prevent recurrent strep infections and heart damage)

Yaws, bejel, and pinta (tropical skin infections caused by treponemal bacteria related to syphilis)

Diphtheria prophylaxis (elimination of the carrier state)

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Lentocilin Dosage

Dosing varies by indication. All doses are given by deep intramuscular injection:

Group A strep (adults): 1,200,000 units single dose

Early syphilis (primary/secondary/early latent): 2,400,000 units single dose (given as two separate 1,200,000-unit injections at two sites)

Late latent / tertiary syphilis: 2,400,000 units once weekly × 3 consecutive weeks

Rheumatic fever prophylaxis: 1,200,000 units every 4 weeks (monthly)

Yaws/bejel/pinta: 1,200,000 units single dose

How Is Lentocilin Different From Bicillin L-A?

Lentocilin and Bicillin L-A contain the same active ingredient and are used for the same indications. Key differences:

Form: Lentocilin = powder for reconstitution (add diluent before use); Bicillin L-A = prefilled syringe (ready to use)

Diluent: Lentocilin includes a 4 mL lidocaine 1.5% diluent; Bicillin L-A does not contain lidocaine

Soy content: Lentocilin contains soy phospholipids; Bicillin L-A does not

Volume: 4 mL per 1,200,000 unit dose (Lentocilin) vs 2 mL (Bicillin L-A)

Regulatory status: Lentocilin = not FDA-approved (imported under enforcement discretion); Bicillin L-A = FDA-approved

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Is Lentocilin Available Near Me?

Due to the ongoing shortage, Lentocilin availability varies significantly by location and week. medfinder contacts clinics and pharmacies near you to find which ones have your medication in stock. Public health STI clinics are often the most reliable source. For more, see our guide on how to find Lentocilin near you.