What is the appropriate dose of ampicillin (Ampicillin) for an 8kg pediatric patient with no known allergies to penicillins (Penicillins)?

Ampicillin Dosing for 8kg Pediatric Patient

For an 8kg child, administer ampicillin 100 mg/kg/day divided into four equal doses (200 mg every 6 hours) for genitourinary or gastrointestinal tract infections, or 50 mg/kg/day divided into three to four equal doses (approximately 100-135 mg per dose) for respiratory tract infections. 1

Weight-Based Dosing Framework

For Genitourinary or Gastrointestinal Tract Infections

• The FDA-approved dosing for pediatric patients weighing ≤20 kg is 100 mg/kg/day total, divided into four equally spaced doses 1
• For this 8kg patient, this translates to 800 mg/day total, or 200 mg every 6 hours 1
• Severe or chronic infections may require larger doses beyond the standard 100 mg/kg/day 1

For Respiratory Tract Infections

• The FDA-approved dosing for pediatric patients weighing ≤20 kg is 50 mg/kg/day total, divided into three to four equally spaced doses 1
• For this 8kg patient, this translates to 400 mg/day total, or approximately 100-135 mg per dose depending on whether divided into four or three daily doses 1

Indication-Specific Considerations for Serious Infections

Endocarditis (Enterococcal or Resistant Streptococcal)

• For relatively penicillin-resistant organisms including enterococci, the American Heart Association recommends 200-300 mg/kg/day IV divided every 4-6 hours 2
• For this 8kg patient, this would be 1,600-2,400 mg/day total, or 267-400 mg every 4 hours (up to a maximum of 12 g daily in adults) 2
• This higher dosing is reserved for serious infections like infective endocarditis and requires combination with gentamicin for the first 2 weeks 2

Critical Administration Guidelines

Timing and Absorption

• Ampicillin must be administered at least 30 minutes before meals or 2 hours after meals for maximal absorption, as gastric acid degradation is minimized but food significantly reduces bioavailability 1

Duration of Therapy

• Continue treatment for a minimum of 48-72 hours after the patient becomes asymptomatic or bacterial eradication is documented 1
• For streptococcal infections, treat for a minimum of 10 days to prevent rheumatic fever or glomerulonephritis 1
• Chronic urinary or gastrointestinal infections may require several weeks of treatment with frequent bacteriologic monitoring 1

Common Pitfalls to Avoid

• Never use doses smaller than those indicated above, as subtherapeutic dosing promotes resistance and treatment failure 1
• Do not exceed adult maximum doses (typically not relevant for an 8kg child, but doses for children should not exceed adult recommendations) 1
• Ensure proper spacing of doses—every 6 hours for GI/GU infections, every 6-8 hours for respiratory infections—to maintain adequate serum levels 1