Ampicillin Dosage and Treatment Protocol for Bacterial Infections
The recommended dosage of ampicillin for bacterial infections varies by infection type, with adults typically receiving 500 mg four times daily for genitourinary or gastrointestinal infections, 250 mg four times daily for respiratory infections, and specific regimens for other conditions such as uncomplicated urinary tract infections where 18-30 g/day IV in divided doses is appropriate. 1
Adult Dosing Guidelines
Oral Administration
- For genitourinary or gastrointestinal tract infections: 500 mg four times daily in equally spaced doses; severe or chronic infections may require larger doses 1
- For respiratory tract infections: 250 mg four times daily in equally spaced doses 1
- For gonorrhea: Single oral dose of 3.5 grams administered simultaneously with 1 gram of probenecid 1
- Administer at least 30 minutes before or 2 hours after meals for maximal absorption 1
Intravenous Administration
- For uncomplicated urinary tract infections (VRE): 18-30 g/day IV in divided doses 2
- For infective endocarditis: 200-300 mg/kg/day IV divided every 4-6 hours up to 12 g daily 2
- For HACEK group infections: 200-300 mg/kg/day IV divided every 4-6 hours up to 12 g daily 2
Pediatric Dosing Guidelines
Children weighing ≤20 kg:
- For genitourinary or gastrointestinal tract infections: 100 mg/kg/day total, divided into four equal doses 1
- For respiratory tract infections: 50 mg/kg/day total, in equally divided doses three to four times daily 1
Neonates and Infants:
- Gestational age >34 weeks, postnatal age ≤7 days: 50 mg/kg/dose IV every 12 hours 2
- Gestational age >34 weeks, postnatal age >7 days: 75 mg/kg/dose IV every 12 hours 2
- Gestational age >34 weeks: 50 mg/kg/dose IV every 8 hours 2
Treatment Duration by Infection Type
- Uncomplicated urinary tract infections: 3-7 days 2
- Infective endocarditis: Generally 4-6 weeks 2
- Streptococcal infections with hemolytic strains: Minimum of 10 days to prevent rheumatic fever or glomerulonephritis 1
- Chronic urinary or gastrointestinal infections: Several weeks with frequent bacteriologic and clinical assessment 1
Special Considerations
For Specific Pathogens:
- For vancomycin-resistant enterococci (VRE) in uncomplicated UTIs: Ampicillin 18-30 g/day IV in divided doses or amoxicillin 500 mg PO/IV every 8 hours 2
- For HACEK group infections: Ampicillin 200-300 mg/kg/day IV divided every 4-6 hours (up to 12 g daily) plus aminoglycoside 2
Important Monitoring:
- For chronic infections: Frequent bacteriologic and clinical assessment during therapy and potentially for several months afterward 1
- In streptococcal infections: Monitor for at least 10 days to prevent complications 1
- For high-dose regimens: Monitor for adverse effects, though comparative studies suggest low-dose regimens (150 mg/kg/day) may be as effective as high-dose (400 mg/kg/day) in certain conditions like bacterial meningitis 3
Common Pitfalls and Caveats
- Ampicillin should not be used for HACEK microorganisms without susceptibility testing due to increasing β-lactamase production; ceftriaxone is preferred 2
- Dosages should not be lower than recommended as this may lead to treatment failure 1
- Previously, ampicillin was considered the preferred drug for bacterial meningitis, but resistance patterns have changed treatment approaches 3
- When treating endocarditis caused by enterococci, combination therapy with gentamicin is often required for the first 2 weeks 2
- For outpatient parenteral therapy, continuous infusion with therapeutic drug monitoring may be required due to ampicillin's short half-life and instability in solution 4
By following these dosing guidelines and considering the specific infection type, patient characteristics, and pathogen susceptibility, clinicians can optimize ampicillin therapy for bacterial infections.