Benzathene Penicillin

# Benzathene penicillin ## Overview - **Classification**: Long-acting penicillin G, Beta-lactam antibiotic. - **Mechanism**: Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), leading to cell lysis. ## Primary Indications 1. **Syphilis** - Treatment of primary, secondary, early latent, and late latent syphilis. 2. **Streptococcal Pharyngitis** - Treatment of Group A Streptococcus (GAS) pharyngitis. 3. **Rheumatic Fever Prophylaxis** - Secondary prophylaxis of rheumatic fever. ## Adult Dosing ### Standard Dosing **Streptococcal Pharyngitis (Group A Strep)** - **Dose**: **1.2 million units** - **Frequency**: Single dose - **Route**: Intramuscular (IM) - **Duration**: Single dose **Syphilis (Primary, Secondary, Early Latent - duration ≤ 1 year)** - **Dose**: **2.4 million units** - **Frequency**: Single dose - **Route**: Intramuscular (IM) **Syphilis (Late Latent, Tertiary, or Unknown Duration)** - **Dose**: **2.4 million units** - **Frequency**: Once weekly for 3 doses - **Route**: Intramuscular (IM) - **Duration**: Total of **7.2 million units** over 3 weeks **Rheumatic Fever Prophylaxis (Secondary)** - **Dose**: **1.2 million units** - **Frequency**: Every 3 to 4 weeks - **Route**: Intramuscular (IM) - **Duration**: Varies based on risk (e.g., 5-10 years, or until age 21-40) ### Dose Adjustments - **Renal Impairment**: Not routinely required due to slow absorption and excretion. Use with caution in severe impairment as small amounts are renally cleared. - **Hepatic Impairment**: No specific adjustments required. - **Elderly Patients**: No specific dose adjustments. Use with caution given potential for reduced renal function. ## Pediatric Dosing ### Neonates (0-28 days) **Congenital Syphilis (Uncomplicated, no CNS involvement)** - **Dose**: **50,000 units/kg** - **Frequency**: Single dose - **Maximum**: **2.4 million units** - **Special Notes**: IV penicillin G is preferred for confirmed neurosyphilis or high-risk cases. ### Infants (1-12 months) **Streptococcal Pharyngitis (Group A Strep) - for children < 27 kg** - **Dose**: **600,000 units** - **Frequency**: Single dose - **Maximum**: **600,000 units** **Congenital Syphilis (late congenital, children > 1 month)** - **Dose**: **50,000 units/kg** - **Frequency**: Single dose - **Maximum**: **2.4 million units** ### Children (1-12 years) **Streptococcal Pharyngitis (Group A Strep)** - **Dose**: **600,000 units** (for children < 27 kg); **1.2 million units** (for children ≥ 27 kg) - **Frequency**: Single dose - **Maximum**: **1.2 million units** **Syphilis (Acquired - Primary/Secondary/Early Latent)** - **Dose**: **50,000 units/kg** - **Frequency**: Single dose - **Maximum**: **2.4 million units** **Rheumatic Fever Prophylaxis (Secondary)** - **Dose**: **1.2 million units** - **Frequency**: Every 3 to 4 weeks - **Maximum**: **1.2 million units** ### Adolescents (13-18 years) - **Dose**: Adult dosing applies. - **Maximum**: Adult dose. ## Safety Information ### Contraindications - **Absolute**: History of hypersensitivity (e.g., anaphylaxis, severe rash) to penicillin or other beta-lactam antibiotics. - **Relative**: History of severe allergic reaction to cephalosporins (potential cross-reactivity). ### Common Adverse Effects - **Very Common (>10%)**: Pain, tenderness, or sterile abscess at injection site. - **Common (1-10%)**: Hypersensitivity reactions (rash, urticaria, pruritus), nausea, diarrhea. - **Serious but Rare**: Anaphylaxis, Jarisch-Herxheimer reaction (fever, chills, headache, myalgia in syphilis treatment), seizures (with inadvertent IV administration), severe cutaneous reactions (SJS, TEN). ### Key Drug Interactions - **Methotrexate**: May increase methotrexate levels due to decreased renal tubular secretion; monitor for toxicity. - **Warfarin**: May enhance anticoagulant effect by altering gut flora; monitor INR. - **Tetracyclines/Chloramphenicol**: May antagonize bactericidal effect of penicillin; avoid concurrent use. ## Monitoring & Follow-up - **Before Treatment**: Assess for history of penicillin allergy. - **During Treatment**: Monitor for signs of allergic reaction for at least 30 minutes post-injection. - **Clinical Signs**: Monitor for Jarisch-Herxheimer reaction in syphilis patients (fever, chills, headache within 24 hours of first dose). This reaction is usually self-limiting. - **Follow-up**: For syphilis, serologic testing (VDRL/RPR) at 6 and 12 months after treatment, then annually if previously HIV-infected. ## Clinical Pearls - 💡 **Administration**: Administer via deep IM injection only. NOT for IV, intra-arterial, or subcutaneous administration. - 💡 **Preparation**: Shake vial vigorously before use to ensure a uniform suspension. - 💡 **Pain**: Injection is often painful. Consider local anesthetic mixed with penicillin, though not universally practiced. - 💡 **Syphilis treatment**: Penicillin G benzathene remains the drug of choice for syphilis. - 💡 **Jarisch-Herxheimer**: Counsel syphilis patients about the possibility of a transient fever/flu-like reaction after the first dose. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.