Extencilline: A long-acting benzathine benzylpenicillin
Extencilline is an antibiotic that contains the active substance benzathine benzylpenicillin, also known as penicillin G benzathine. It belongs to the penicillin class of antibiotics, which are known for their effectiveness against a range of susceptible bacteria. Unlike some oral antibiotics, Extencilline is administered exclusively by deep intramuscular (IM) injection. Its long-acting formulation ensures that a single injection provides a sustained, therapeutic level of the antibiotic in the body over an extended period.
Why was Extencilline introduced in the US?
In the United States, Extencilline was temporarily imported starting in 2024 to help mitigate a nationwide shortage of its domestic equivalent, Bicillin L-A®. The FDA and CDC authorized its use, particularly for treating syphilis, including cases in pregnant individuals, due to the critical nature of this treatment. While Extencilline and Bicillin L-A share the same active ingredient, there are important differences in their formulation, preparation, and labeling that healthcare providers must be aware of.
How Extencilline works
As a beta-lactam antibiotic, Extencilline works by targeting and disrupting the growth and replication of bacteria. Specifically, it functions by inhibiting the biosynthesis of the bacterial cell wall, a crucial protective layer that allows bacteria to survive.
- Targeted action: Extencilline targets penicillin-binding proteins (PBPs), which are essential for forming the peptidoglycan layer of the cell wall during active bacterial multiplication.
- Cell wall lysis: By inhibiting PBPs, the antibiotic weakens the cell wall, making it osmotically unstable.
- Bacterial destruction: The weakened cell wall can no longer withstand the internal pressure of the cell, leading to cell wall lysis and the subsequent death of the bacterium.
The long-acting nature of benzathine benzylpenicillin is a key feature, as it is slowly released into the bloodstream over time, maintaining a consistent therapeutic concentration.
Medical uses of Extencilline
Extencilline is indicated for the treatment and prophylaxis of several infections caused by susceptible bacteria. Its uses include:
- Treatment of Syphilis: This is one of its primary uses, treating primary, secondary, and latent syphilis (excluding neurosyphilis) in adults and children.
- Treatment of Yaws and Pinta: Extencilline is effective against these tropical infectious skin diseases caused by Treponema species.
- Treatment of Erysipelas: This is a specific type of skin infection caused by streptococcal bacteria.
- Prophylaxis of Rheumatic Fever: It is used for the long-term prevention of acute rheumatic fever and its associated complications, such as rheumatic carditis.
- Prophylaxis of Post-streptococcal Glomerulonephritis: The antibiotic can also prevent this specific type of kidney inflammation that may follow a streptococcal infection.
Important administration and safety considerations
Administration of Extencilline is strictly limited to deep intramuscular injection. Inadvertent intravenous administration is fatal and has been associated with cardiorespiratory arrest. The powdered formulation requires aseptic reconstitution with a diluent, which can be sterile water or a lidocaine solution.
- Allergy Warning: As a penicillin, it is contraindicated in patients with a history of hypersensitivity to penicillins or cephalosporins. Extencilline also contains soy phospholipids, making it contraindicated for individuals with soy or peanut allergies.
- Injection Site: The injection must be administered into a deep muscle, such as the upper, outer quadrant of the gluteus maximus. Repeated injections may require varying the site.
- Neurovascular Risk: Injections should be done with caution to avoid hitting a nerve or artery, as this can cause permanent neurological damage or other severe complications.
Comparison of Extencilline vs. Bicillin L-A®
During periods of drug shortages, it is critical for healthcare professionals to understand the differences between the temporarily imported Extencilline and the standard U.S. product, Bicillin L-A®. The following table highlights key distinctions based on FDA communications.
| Feature | Extencilline (Imported) | Bicillin L-A® (Standard US) |
|---|---|---|
| Dosage Form | Powder for reconstitution, vial and diluent | Prefilled, disposable syringes with injectable suspension |
| Preparation | Requires aseptic reconstitution with water or lidocaine solution; used immediately after mixing | Ready-to-use injectable suspension |
| Reconstitution Volume | Higher volume per dose: 5 mL for 1.2M units, 7 mL for 2.4M units | Lower volume per dose: 2 mL for 1.2M units, 4 mL for 2.4M units |
| Storage | Powder does not require special storage; reconstituted suspension must be used immediately | Requires refrigeration (36-46°F) |
| Boxed Warning | Labeling does not have a U.S. boxed warning; providers refer to Bicillin L-A labeling | Includes boxed warning: “Fatal if given by other routes” |
| Allergen | Contains soy phospholipids; contraindicated for soy/peanut allergy | Does not contain soy phospholipids |
Conclusion
Extencilline represents a vital resource for healthcare systems experiencing shortages of Bicillin L-A®, particularly for conditions like syphilis where treatment continuity is paramount. As an imported form of benzathine benzylpenicillin, it provides the same therapeutic benefit as its American counterpart by inhibiting bacterial cell wall synthesis. However, critical differences in its formulation as a powder requiring reconstitution, larger injection volumes, and specific allergen warnings demand careful attention from prescribers and administrators. The necessity of deep intramuscular injection and the severe risks of accidental IV administration underscore the importance of strict adherence to administration protocols. Healthcare providers are advised to follow official guidance from the CDC and FDA regarding its use during active shortages to ensure patient safety and effective treatment. Find more information on drug shortages and related guidance here.
