What is the appropriate antibiotic dosing regimen for a 59‑kg adult with confirmed or suspected Weil’s disease (severe leptospirosis)?

Antibiotic Dosing for Weil's Disease in a 59‑kg Patient

For a 59‑kg adult with severe leptospirosis (Weil's disease), administer ceftriaxone 2 g intravenously once daily for 7 days, or alternatively penicillin G 1.5 million units intravenously every 6 hours for 7 days. 1

Immediate Treatment Priorities

Start antibiotics immediately upon clinical suspicion—do not wait for serological confirmation, as delay increases mortality. 1 Serology is often negative in the first week, and the bacteremic phase requires urgent intervention. 1

Primary Antibiotic Regimens for Severe Disease

• Ceftriaxone 2 g IV once daily for 7 days is the preferred regimen due to superior convenience, safety profile, and proven efficacy in severe leptospirosis. 1, 2 This single daily dose offers practical advantages over penicillin's four‑times‑daily schedule while maintaining excellent outcomes. 2

• Penicillin G 1.5 million units IV every 6 hours for 7 days remains an acceptable alternative, though it requires more frequent dosing. 1

Weight‑Based Dosing Considerations

For this 59‑kg patient, both regimens use standard adult dosing rather than weight‑based calculations:

• Ceftriaxone: The fixed dose of 2 g daily applies regardless of body weight in adults with normal renal function. 1, 2
• Penicillin G: The 1.5 million units every 6 hours (6 million units total daily) is the standard adult dose. 1

Clinical Context and Severity Assessment

Weil's disease represents the severe form of leptospirosis, characterized by:

• Jaundice with hepatorenal syndrome—marked hyperbilirubinemia with modest transaminase elevations. 1
• Acute kidney injury occurring in approximately 30% of severe cases. 1
• Hemorrhagic manifestations in roughly 50% of severe cases, driven by capillary fragility rather than coagulopathy (PT/PTT typically normal despite bleeding). 1
• Thrombocytopenia frequently accompanies the hemorrhagic syndrome. 1

Supportive Care Requirements

Beyond antibiotics, severe leptospirosis demands aggressive supportive management:

• Fluid resuscitation: Administer isotonic crystalloid or colloid up to 60 mL/kg as three boluses of 20 mL/kg if shock is present, reassessing after each bolus. 1
• ICU consultation should occur early if repeated fluid boluses are needed or circulatory failure develops. 1
• Renal support: Monitor closely for acute kidney injury requiring dialysis. 1
• Respiratory monitoring: Methylprednisolone 0.5–1.0 mg/kg IV daily for 1–2 weeks may be used for pulmonary hemorrhage complications. 1

Alternative Antibiotics (If Primary Agents Unavailable)

• Doxycycline 100 mg orally twice daily for 7 days is appropriate only for mild‑to‑moderate disease, not severe Weil's disease requiring IV therapy. 1
• Amoxicillin or tetracycline may substitute for doxycycline in mild cases but are inadequate for severe disease. 1

Treatment Response and Monitoring

• Expect clinical improvement within 3 days of antibiotic initiation. 1 If no improvement occurs, reassess for complications or alternative diagnoses.
• Follow‑up 2 days after starting treatment for seriously ill patients to evaluate response and adjust management. 1
• Do not discontinue antibiotics early despite clinical improvement—complete the full 7‑day course. 1

Common Pitfalls to Avoid

• Do not wait for positive serology before starting antibiotics, as early serologic tests are frequently negative. 1 The biphasic illness pattern and characteristic clinical features (conjunctival suffusion, severe myalgias, jaundice) should trigger immediate empiric treatment. 1

• Do not rely on normal coagulation studies to rule out hemorrhagic complications—PT, PTT, and fibrinogen remain normal despite active bleeding due to capillary fragility rather than consumptive coagulopathy. 1

• Do not mistake leptospirosis for viral hepatitis in patients presenting with fever and jaundice; the combination of jaundice, renal failure, and thrombocytopenia strongly suggests Weil's disease. 1

Renal Dose Adjustments

If acute kidney injury develops during treatment:

• Ceftriaxone requires no dose adjustment unless both severe renal and hepatic impairment coexist (not specified in provided evidence, but standard practice maintains 2 g daily with isolated renal failure).
• Penicillin G may require interval extension in severe renal failure, though specific guidance is not provided in the cited guidelines.