What is the recommended dose of ampicillin (Ampicillin) for adults and children?

Ampicillin Dosage Recommendations for Adults and Children

For adults, the recommended dose of ampicillin is 500 mg four times daily for most infections, while children weighing 20 kg or less should receive 100 mg/kg/day divided into four equal doses for genitourinary or gastrointestinal infections, and 50 mg/kg/day divided into 3-4 doses for respiratory infections. 1

Adult Dosing

Standard Dosing

• Genitourinary/Gastrointestinal infections: 500 mg four times daily in equally spaced doses 1
• Respiratory tract infections: 250 mg four times daily in equally spaced doses 1
• Severe or chronic infections: May require larger doses 1

Special Situations

• Gonorrhea: Single oral dose of 3.5 grams of ampicillin administered simultaneously with 1 gram of probenecid 1
• Endocarditis prophylaxis: 2.0 g IM or IV within 30 minutes before procedure 2

Pediatric Dosing

Children weighing 20 kg or less

• Genitourinary/Gastrointestinal infections: 100 mg/kg/day total, divided into four equal doses 1
• Respiratory tract infections: 50 mg/kg/day total, divided into 3-4 equal doses 1

Neonatal dosing (based on weight and age)

• Postnatal age ≤7 days and ≤2000 g: 50 mg/kg/day divided every 12 hours 2
• Postnatal age ≤7 days and >2000 g: 75 mg/kg/day divided every 8 hours 2
• Postnatal age >7 days and <1200 g: 50 mg/kg/day divided every 12 hours 2
• Postnatal age >7 days and 1200-2000 g: 75 mg/kg/day divided every 8 hours 2
• Postnatal age >7 days and >2000 g: 100 mg/kg/day divided every 6 hours 2

Infants and children (beyond neonatal period)

• Standard dosing: 100-200 mg/kg/day divided every 6 hours 2
• Intra-abdominal infections: 200 mg/kg/day divided every 6 hours 2

Administration Guidelines

• Administer at least 30 minutes before or 2 hours after meals for maximal absorption 1
• For streptococcal infections, minimum 10 days treatment is recommended to prevent rheumatic fever or glomerulonephritis 1
• For chronic urinary or gastrointestinal infections, frequent bacteriologic and clinical assessment is necessary during therapy and potentially for several months afterward 1

Special Considerations

1. Duration of therapy:

   • Continue for minimum 48-72 hours after patient becomes asymptomatic 1
   • For streptococcal infections: minimum 10 days 1
   • For stubborn infections: may require several weeks of treatment 1

2. Dosage adjustments:

   • Larger doses may be required for severe or chronic infections in all patients 1
   • Doses for children should not exceed doses recommended for adults 1

3. Efficacy considerations:

   • Studies show that ampicillin at 100 mg/kg/day divided into 4 doses is effective for urinary tract infections in children 3
   • For combination therapy with sulbactam, 200 mg of ampicillin plus 100 mg of sulbactam per kg/day has shown 98.7% cure rate in pediatric infections 4

Common Pitfalls and Caveats

• Using inadequate doses for severe infections can lead to treatment failure
• Not completing the full course of therapy, especially for streptococcal infections, can lead to complications like rheumatic fever
• Failure to adjust dosing based on patient age and weight in pediatric populations
• Not accounting for the possibility of ampicillin-resistant organisms, particularly in urinary tract infections where resistance can develop 3
• Administering with food, which can reduce absorption 1

Always ensure that the appropriate dose is selected based on the patient's age, weight, infection site, and severity to optimize treatment outcomes while minimizing adverse effects.