Ampicillin Oral Dosage and Treatment Duration for Susceptible Bacterial Infections
For adults and children weighing over 20 kg, the recommended oral ampicillin dosage for most susceptible bacterial infections is 500 mg four times daily in equally spaced doses. 1
Adult Dosing Guidelines
- For genitourinary or gastrointestinal tract infections (except gonorrhea): 500 mg four times daily; 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: A single oral dose of 3.5 grams of ampicillin administered simultaneously with 1 gram of probenecid 1
Pediatric Dosing Guidelines
- For children weighing 20 kg or less with genitourinary or gastrointestinal tract infections: 100 mg/kg/day total, divided into four equal doses 1
- For children weighing 20 kg or less with respiratory tract infections: 50 mg/kg/day total, divided into three to four equal doses daily 1
- Doses for children should not exceed doses recommended for adults 1
Treatment Duration by Infection Type
- For most susceptible bacterial infections: Minimum of 48 to 72 hours after the patient becomes asymptomatic or evidence of bacterial eradication has been obtained 1
- For infections caused by hemolytic strains of streptococci: Minimum of 10 days to prevent rheumatic fever or glomerulonephritis 1
- For chronic urinary or gastrointestinal infections: Treatment may be necessary for several weeks with frequent bacteriologic and clinical assessment 1
- For animal bite infections: Ampicillin is listed as a treatment option, typically administered for 3-7 days 2
Special Administration Considerations
- Ampicillin should be administered at least one-half hour before or two hours after meals for maximal absorption, despite being resistant to degradation by gastric acid 1
- Smaller doses than those indicated in the guidelines should not be used 1
- For stubborn infections, treatment for several weeks may be necessary 1
Important Considerations for Specific Infections
- For skin and soft tissue infections: Ampicillin may be used as part of combination therapy for certain infections 2
- For streptococcal pharyngitis: While not the first-line agent, ampicillin can be considered when appropriate, with dosing similar to amoxicillin (50 mg/kg once daily, maximum 1,000 mg) for 10 days 2
- For uncomplicated urinary tract infections: Treatment duration of 3-7 days is typically sufficient 3
Pitfalls and Caveats
- Ampicillin is not recommended for empiric treatment of Salmonella gastroenteritis, as studies show no benefit and increased risk of bacteriologic and symptomatic relapse 4
- When treating chronic carriers of Group A Streptococcus, ampicillin alone may be less effective than other regimens 2
- For meningitis, intravenous rather than oral ampicillin is typically recommended 5
- Resistance patterns should be considered when selecting ampicillin for treatment, particularly for gram-negative infections 2
Remember that ampicillin dosing and duration should be adjusted based on the severity of infection, patient factors, and local resistance patterns. Regular monitoring for clinical response is essential, particularly for more severe or chronic infections.