What is the dosing regimen for Penicillin?

Penicillin V (Pentid) Dosing

For most common infections in adults, penicillin V should be dosed at 250-500 mg orally every 6-8 hours, with specific dosing determined by infection type and severity. 1

Standard Adult Dosing by Indication

Streptococcal Pharyngitis/Tonsillitis

• Standard regimen: 250-500 mg (400,000-800,000 units) every 6-8 hours for 10 days 1
• Alternative regimen: 500 mg twice daily for 10 days is equally effective as four-times-daily dosing 2
• Short-course option: 800 mg four times daily for 5 days has been shown non-inferior to the 10-day regimen for group A streptococcal pharyngotonsillitis 3
• Avoid once-daily dosing: Single daily dosing results in significantly higher treatment failure rates (23% vs 8%) 2

Pneumococcal Respiratory Infections

• Dosing: 250-500 mg (400,000-800,000 units) every 6 hours until afebrile for at least 2 days 1
• This includes otitis media and mild to moderately severe respiratory tract infections 1

Staphylococcal Skin/Soft Tissue Infections

• Dosing: 250-500 mg (400,000-800,000 units) every 6-8 hours 1
• Culture and sensitivity testing should be performed before initiating therapy 1

Vincent's Infection (Fusospirochetosis)

• Dosing: 250-500 mg (400,000-800,000 units) every 6-8 hours 1

Rheumatic Fever Prophylaxis

• Dosing: 125-250 mg (200,000-400,000 units) twice daily on a continuing basis 1

Bacterial Endocarditis Prophylaxis

• Pre-procedure: 2 grams 1 hour before dental or upper respiratory tract procedures 1
• Post-procedure: 1 gram 6 hours after the initial dose 1

Pediatric Dosing (Children ≥12 years)

General Infections

• Follow adult dosing recommendations for children 12 years and older 1

Children Under 60 lbs (Endocarditis Prophylaxis)

• Pre-procedure: 1 gram 1 hour before procedure 1
• Post-procedure: 500 mg 6 hours after initial dose 1

Younger Children (Specific Infections)

• Streptococcal pharyngitis: 25-50 mg/kg/day in divided doses 2-4 times daily 4
• Asplenic patients (prophylaxis): 125 mg twice daily for children under 5 years; 250 mg twice daily for ages 5-14 years 4
• Asplenic patients (treatment): 200-300 mg/kg/day in 6 divided doses (maximum 6 g) for ages 5-14 years 4

Critical Dosing Considerations

Frequency Matters for Efficacy

• Time-dependent killing: Penicillin is a time-dependent antibiotic requiring adequate time above MIC 5
• Twice-daily dosing (500 mg) is as effective as four-times-daily dosing (250 mg) for streptococcal pharyngitis 2
• Once-daily dosing should be avoided due to significantly higher failure rates 2

Duration of Therapy

• Standard duration: 10 days remains the traditional recommendation for most streptococcal infections 1
• Short-course alternative: 5 days of higher-frequency dosing (800 mg four times daily) is non-inferior for group A streptococcal pharyngotonsillitis 3
• The 5-day regimen reduces total antibiotic exposure from 30g to 16g while maintaining efficacy 3

Common Pitfalls to Avoid

• Inadequate dosing: Current perception of declining penicillin effectiveness may be due to inadequate dosing rather than true resistance 6
• Premature discontinuation: Patients must complete the full course even if symptoms resolve earlier 1
• Storage: Reconstituted oral solution must be refrigerated and discarded after 14 days 1

Special Populations

Syphilis Treatment

• Early latent syphilis: Benzathine penicillin G 2.4 million units IM single dose (not oral penicillin V) 4
• Late latent syphilis: Benzathine penicillin G 7.2 million units total (three weekly doses of 2.4 million units IM) 4
• Oral penicillin V is not appropriate for syphilis treatment 4

Asplenic Patients

• Prophylaxis: 250-500 mg twice daily for adults 4
• Treatment of suspected infection: 1.2 g every 4-6 hours IV (benzylpenicillin preferred over oral) 4

Penicillin-Allergic Patients

• For streptococcal infections, alternatives include erythromycin 250 mg four times daily or clindamycin 300-400 mg three times daily 4
• For syphilis in non-pregnant patients, doxycycline 100 mg twice daily for 2 weeks (early) or 4 weeks (late) 4