What is the recommended dosage and treatment duration for benzyl penicillin (penicillin G) in adults and children?

Benzyl Penicillin (Penicillin G) Dosing and Treatment Duration

For Group A Streptococcal Pharyngitis, use intramuscular benzathine penicillin G as a single dose: 1.2 million units for patients ≥27 kg or 600,000 units for patients <27 kg, which provides optimal compliance and eradication rates. 1

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Intramuscular Benzathine Penicillin G (Preferred for Pharyngitis)

Single-dose intramuscular therapy ensures 100% compliance and remains the gold standard for streptococcal pharyngitis, particularly in populations where adherence to 10-day oral regimens cannot be assured. 1

Dosing by Weight:

• ≥27 kg (approximately 60 lbs): 1.2 million units IM as a single dose 1
• <27 kg: 600,000 units IM as a single dose 1

Key Advantages:

• Guarantees compliance by eliminating the need for 10-day oral therapy 1
• Prevents rheumatic fever even when started up to 9 days after symptom onset 1
• Particularly indicated for: patients unlikely to complete oral therapy, those with personal/family history of rheumatic fever, or those in crowded living conditions or low socioeconomic environments 1

Pain Reduction Strategy:

• Warm medication to room temperature before administration to reduce injection discomfort 1
• Combination formulations with procaine penicillin (Bicillin C-R) are less painful than benzathine alone, though the benzathine component must still provide adequate dosing 1

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Intravenous Aqueous Crystalline Penicillin G (For Serious Infections)

For severe invasive infections, IV penicillin G dosing ranges from 12-24 million units/day divided every 4-6 hours, with specific dosing determined by infection type and severity. 2

Adult Dosing by Indication:

Streptococcal Endocarditis/Serious Pneumonia:

• 12-20 million units/day IV in divided doses every 4-6 hours 2
• Duration: 4 weeks for endocarditis 1

Meningococcal Meningitis/Septicemia:

• 24 million units/day IV as 2 million units every 2 hours 2

Neurosyphilis:

• 12-24 million units/day IV as 2-4 million units every 4 hours for 10-14 days 2
• Many experts recommend additional benzathine penicillin G 2.4 million units IM weekly for 3 doses after IV therapy completion 2

Listeria Meningitis:

• 15-20 million units/day IV for 2 weeks 2

Listeria Endocarditis:

• 15-20 million units/day IV for 4 weeks 2

Cutaneous Anthrax (Community-Acquired):

• 8-12 million units/day IV in divided doses every 4-6 hours 1

Pediatric Dosing by Indication:

Gonococcal Infections (Arthritis, Meningitis, Endocarditis):

• <45 kg: 100,000 units/kg/day IV in 4 equally divided doses for arthritis (7-10 days); 250,000 units/kg/day every 4 hours for meningitis (10-14 days) or endocarditis (4 weeks) 2
• ≥45 kg: 10 million units/day IV in 4 equally divided doses, duration depends on infection type 2

Congenital/Neurosyphilis (After Newborn Period):

• 200,000-300,000 units/kg/day IV (administered as 50,000 units/kg every 4-6 hours) for 10-14 days 2

Cutaneous Anthrax (Community-Acquired):

• 100,000-150,000 units/kg/day IV in divided doses every 4-6 hours 1

Diphtheria (Adjunctive to Antitoxin):

• 150,000-250,000 units/kg/day IV in equal doses every 6 hours for 7-10 days 2

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Oral Penicillin V (Alternative for Pharyngitis)

Oral penicillin V requires strict 10-day adherence but is acceptable when compliance can be assured through patient counseling. 1

Dosing:

• Children: 250 mg PO twice or three times daily for 10 days 1
• Adolescents/Adults: 250 mg PO three to four times daily OR 500 mg PO twice to three times daily for 10 days 1

Critical Duration Requirement:

• Full 10-day course is mandatory to achieve maximal pharyngeal eradication and prevent rheumatic fever 1
• Patients become non-contagious after 24 hours of therapy, but must complete the full course 1

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Renal Impairment Adjustments

Penicillin G is relatively nontoxic, requiring dosage adjustments only in severe renal impairment. 2

• Creatinine clearance <10 mL/min/1.73 m²: Full loading dose, then half the loading dose every 8-10 hours 2
• Creatinine clearance >10 mL/min/1.73 m²: Full loading dose, then half the loading dose every 4-5 hours 2
• Additional modifications needed for combined hepatic and renal impairment 2

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Critical Treatment Principles

Minimum Treatment Duration:

• Acute infections: Continue therapy 48-72 hours after patient becomes asymptomatic 2
• Group A streptococcal infections: Maintain therapy for at least 10 days to reduce rheumatic fever risk 2

Penicillin Resistance:

• No penicillin-resistant Group A streptococcus has ever been documented worldwide, making penicillin the definitive choice for susceptible streptococcal infections 1

Common Pitfall to Avoid:

• Never shorten the 10-day course for streptococcal pharyngitis, even if symptoms resolve in 3-4 days, as this increases treatment failure rates and rheumatic fever risk 1
• Do not use penicillin G formulations requiring <1 million units per dose in pediatric patients 2