## Drug of Choice for Immune-Phase Leptospirosis **Key Point:** Doxycycline (or tetracycline) is the first-line agent for immune-phase leptospirosis (after day 7) because leptospires are sequestered in tissues and immune complexes dominate the pathology. Oral bioavailability is adequate. ### Why Doxycycline in Immune Phase? 1. **Tissue penetration:** Leptospires are no longer in bloodstream; they reside in kidneys, eyes, and CNS. 2. **Oral efficacy:** Doxycycline achieves therapeutic levels in urine and ocular tissues. 3. **Immune modulation:** Reduces inflammatory complications (uveitis, aseptic meningitis). 4. **Convenience:** Oral dosing allows outpatient management of uncomplicated cases. **High-Yield:** The transition from penicillin G (leptospiremic phase) to doxycycline (immune phase) at day 7–8 is a classic NEET PG concept. Uveitis appearing on day 10 signals immune-phase disease. ### Dosing - **Doxycycline:** 100 mg orally twice daily for 7 days - **Alternative (if doxycycline contraindicated):** Tetracycline 500 mg orally four times daily **Clinical Pearl:** Uveitis in leptospirosis is immune-mediated (antigen–antibody complex deposition), not due to active leptospiremia. This explains why oral agents suffice. **Warning:** Continuing high-dose IV penicillin into the immune phase is unnecessary and wasteful. The switch to oral doxycycline should occur by day 7–8 in improving patients. [cite:Park 26e Ch 7]
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