Usage
Benzathine penicillin G is an antibiotic primarily used for treating infections caused by susceptible bacteria, particularly Streptococcus pyogenes (Group A Streptococcus) and Treponema pallidum (the causative agent of syphilis).
Pharmacological Classification: Beta-lactam antibiotic, long-acting penicillin.
Mechanism of Action: Benzathine penicillin G inhibits bacterial cell wall synthesis by binding to and inactivating penicillin-binding proteins (PBPs). This leads to cell lysis and bacterial death.
Alternate Names
Benzathine benzylpenicillin.
Brand Names: Bicillin L-A, Permapen.
How It Works
Pharmacodynamics: Bactericidal against susceptible bacteria, primarily gram-positive organisms and spirochetes.
Pharmacokinetics:
- Absorption: Slowly absorbed after intramuscular injection, creating a tissue depot for prolonged release.
- Metabolism: Hydrolyzed to penicillin G.
- Elimination: Primarily renal excretion.
Mode of Action: Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins, leading to cell lysis.
Receptor Binding/Enzyme Inhibition: Inhibits penicillin-binding proteins.
Elimination Pathways: Primarily renal excretion.
Dosage
Standard Dosage
Adults:
- Syphilis (early): 2.4 million units IM single dose.
- Syphilis (late): 2.4 million units IM weekly for 3 weeks.
- Streptococcal pharyngitis: 1.2 million units IM single dose.
Children:
- Syphilis: 50,000 units/kg IM (max 2.4 million units) single dose (early) or weekly for 3 weeks (late).
- Streptococcal pharyngitis: Consult pediatric guidelines for weight-based dosing.
Special Cases:
- Elderly Patients: Initiate at the lower end of the dosing range due to potential decreased renal function. Monitor renal function.
- Patients with Renal Impairment: Dose adjustments are required based on creatinine clearance.
- Patients with Hepatic Dysfunction: Dosage adjustments may be necessary in severe hepatic impairment.
- Patients with Comorbid Conditions: Individualized dosing may be necessary. Consult specialized guidelines.
Clinical Use Cases
Benzathine penicillin G is not typically used in clinical scenarios like intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations requiring rapid antibiotic action. Its slow onset of action makes it unsuitable for these situations. Short-acting penicillins or other appropriate antibiotics are preferred in these clinical settings.
Dosage Adjustments
Dose adjustments are required for patients with renal impairment based on creatinine clearance. Consult specific guidelines for detailed recommendations.
Side Effects
Common Side Effects:
- Pain, swelling, or nodule formation at the injection site.
- Nausea, vomiting, diarrhea.
- Headache, dizziness.
Rare but Serious Side Effects:
- Allergic reactions (rash, hives, itching, difficulty breathing, swelling of face/tongue/throat).
- Jarisch-Herxheimer reaction (fever, chills, headache, muscle aches after starting treatment for syphilis).
- Seizures (rare, usually with high doses or renal impairment).
Long-Term Effects: Generally, no long-term adverse effects are associated with appropriate benzathine penicillin G use.
Contraindications
- Known hypersensitivity to penicillin or any component of the formulation.
Drug Interactions
- Tetracyclines, macrolides: May antagonize bactericidal activity.
- Probenecid: May increase penicillin serum concentrations.
- Methotrexate: Penicillin may reduce methotrexate clearance.
- Oral contraceptives: Efficacy may be reduced (though this is generally not considered clinically significant).
Pregnancy and Breastfeeding
- Pregnancy Safety Category: B (generally considered safe).
- Breastfeeding: Small amounts are excreted in breast milk; generally considered compatible with breastfeeding. Monitor infant for diarrhea or thrush.
Drug Profile Summary
- Mechanism of Action: Inhibits bacterial cell wall synthesis.
- Side Effects: Injection site reactions, gastrointestinal upset, allergic reactions.
- Contraindications: Penicillin hypersensitivity.
- Drug Interactions: Tetracyclines, probenecid, methotrexate.
- Pregnancy & Breastfeeding: Generally safe.
- Dosage: Varies with indication and patient factors; see dosage section.
- Monitoring Parameters: Observe for signs of allergic reaction. Monitor treatment response.
Popular Combinations
Benzathine penicillin G is usually administered as a single agent. Co-administration with other antibiotics is generally avoided due to potential antagonism or lack of added benefit.
Precautions
- General Precautions: Carefully assess for penicillin allergy.
- Specific Populations: Monitor renal function in elderly patients and those with renal impairment.
- Pregnant Women: Generally safe, but benefits should outweigh risks.
- Breastfeeding Mothers: Monitor infant for adverse effects.
- Children & Elderly: Age-specific dosing adjustments are necessary.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Benzathine penicillin G?
A: The dosage varies depending on the indication and patient factors. Refer to the dosage section for specific recommendations.
Q2: What is the route of administration for Benzathine penicillin G?
A: Intramuscular (IM) injection only. Never administer intravenously (IV).
Q3: What are the common side effects of Benzathine penicillin G?
A: Common side effects include pain and swelling at the injection site, nausea, vomiting, and diarrhea.
Q4: Is Benzathine penicillin G safe during pregnancy?
A: It is generally considered safe during pregnancy (Pregnancy Category B).
Q5: Can Benzathine penicillin G be used in patients with a penicillin allergy?
A: No, it is contraindicated in patients with a known penicillin allergy.
Q6: What infections are treated with Benzathine penicillin G?
A: Syphilis, streptococcal pharyngitis, and other infections caused by susceptible bacteria.
Q7: How long does Benzathine penicillin G stay in the system?
A: It is slowly released from a tissue depot, providing therapeutic levels for several weeks after a single dose.
Q8: What should I do if a patient experiences an allergic reaction to Benzathine penicillin G?
A: Discontinue the medication immediately and provide appropriate medical management (antihistamines, epinephrine if necessary).
Q9: What is the difference between Benzathine penicillin G and other penicillins?
A: Benzathine penicillin G is a long-acting formulation, whereas other penicillins (e.g., penicillin V, penicillin G aqueous) have shorter durations of action.
