What is the recommended amoxicillin dosage for an otherwise healthy adult with uncomplicated leptospirosis and the appropriate pediatric dose for children with normal renal and hepatic function?

Amoxicillin Dosing for Leptospirosis

Adult Dosing

For otherwise healthy adults with uncomplicated leptospirosis, amoxicillin is not a first-line agent, but when used, the dose is typically 500 mg orally every 8 hours based on extrapolation from other spirochetal infections. 1

• Amoxicillin is mentioned as a treatment option for leptospirosis, though specific dosing studies are limited. 1
• Penicillin G, doxycycline, ceftriaxone, and cefotaxime remain the preferred first-line agents with stronger evidence. 2, 3
• When amoxicillin is selected (often for outpatient mild disease), the standard regimen is 500 mg orally three times daily (every 8 hours) for 7 days, extrapolated from its use in other spirochetal infections. 1

First-Line Alternatives with Stronger Evidence

• Doxycycline 100 mg orally twice daily for 7 days is a well-established alternative for mild to moderate disease. 2, 4
• Penicillin G 1.5 million units IV every 6 hours for 7 days has long been considered the treatment of choice for severe disease. 2, 3
• Ceftriaxone 1 g IV daily for 7 days is equally effective as penicillin G for severe leptospirosis and offers once-daily dosing convenience. 3

Pediatric Dosing

For children with normal renal and hepatic function, amoxicillin dosing for leptospirosis would be 45-50 mg/kg/day divided into three doses (every 8 hours) for 7 days, with a maximum single dose of 500 mg. 5, 1

• This dosing is extrapolated from pediatric treatment of other bacterial infections and the limited mention of amoxicillin in leptospirosis literature. 5, 1
• For a child weighing 20 kg, this translates to approximately 300-330 mg three times daily. 5
• The maximum daily dose should not exceed 1500 mg/day in children. 5

Pediatric First-Line Alternatives

• Doxycycline is generally avoided in children under 8 years due to dental staining concerns, though it may be considered in severe cases where benefits outweigh risks. 2, 4
• Ceftriaxone 50-75 mg/kg/day IV once daily (maximum 2 g/day) for 7 days is an excellent alternative for hospitalized children with severe disease. 6, 3
• Penicillin G remains an option for severe pediatric leptospirosis at weight-based dosing. 2

Critical Clinical Context

Why Amoxicillin Is Not First-Line

• The evidence base for amoxicillin in leptospirosis is weak compared to penicillin, doxycycline, and ceftriaxone. 2, 7
• A Cochrane review found insufficient high-quality evidence to provide clear antibiotic guidelines for leptospirosis, though penicillin showed promise. 7
• Ceftriaxone and cefotaxime may be preferred agents due to once-daily dosing, broader spectrum, and equivalent efficacy to penicillin. 2, 3

When to Consider Amoxicillin

• Amoxicillin may be reasonable for mild, outpatient leptospirosis when oral therapy is appropriate and the patient cannot tolerate doxycycline. 1
• It should not be used for severe leptospirosis requiring hospitalization—use IV penicillin G or ceftriaxone instead. 2, 3

Treatment Duration and Monitoring

• Standard treatment duration is 7 days for all antibiotic regimens. 3
• Clinical improvement (fever resolution) typically occurs within 3 days of appropriate antibiotic therapy. 3
• If no improvement occurs within 48-72 hours, reassess the diagnosis and consider complications such as Jarisch-Herxheimer reaction or alternative diagnoses. 2

Common Pitfalls to Avoid

• Do not use amoxicillin for severe leptospirosis with jaundice, renal failure, or pulmonary hemorrhage—these patients require IV therapy with penicillin G or ceftriaxone. 2, 3
• Do not underdose: The three-times-daily dosing (every 8 hours) is essential for maintaining adequate serum levels against spirochetes. 1
• Avoid doxycycline in pregnant women and young children unless benefits clearly outweigh risks. 2, 4
• Remember that approximately 10% of leptospirosis cases progress to severe disease (Weil's disease) with significant mortality risk—maintain a low threshold for hospitalization and IV therapy. 1