A 32-year-old man with acute bacillary dysentery caused by Shigella sonnei is hospitalized with severe dehydration and bloody stools. He has a documented allergy to fluoroquinolones. What is the preferred alternative antibiotic?

Explanation

## Alternative Treatment for Shigella in Fluoroquinolone-Allergic Patients **Key Point:** Ceftriaxone is the preferred alternative first-line agent for Shigella when fluoroquinolones are contraindicated (allergy, pregnancy, or resistance). ### Why Ceftriaxone is Preferred 1. **Excellent efficacy** — Third-generation cephalosporin with broad-spectrum coverage against Shigella. 2. **Low resistance rates** — Resistance to cephalosporins in Shigella remains <5–10% globally and in India. 3. **Good tissue penetration** — Achieves adequate concentrations in the colon and intracellular compartments. 4. **Parenteral formulation** — Suitable for severe disease with dehydration and systemic toxicity. 5. **Safety profile** — Well-tolerated in adults; no cross-reactivity with fluoroquinolone allergy. ### Dosing for Severe Shigella Infection - **Ceftriaxone:** 1–2 g IV/IM every 12 hours (or 2 g once daily) for 3–5 days. - Adjust for renal function if needed (though rarely necessary in acute infection). **High-Yield:** Ceftriaxone is the WHO-recommended alternative when fluoroquinolones cannot be used. It is the standard second-line agent in most treatment guidelines. ### Comparison of Alternatives in Fluoroquinolone-Allergic Patients | Agent | Efficacy | Resistance | Penetration | Use | |-------|----------|-----------|-------------|-----| | **Ceftriaxone** | Excellent | Low (<10%) | Good | **Preferred alternative** | | TMP-SMX | Moderate | High (>50%) | Moderate | Not recommended | | Chloramphenicol | Good | Low | Good | Rarely used; toxicity concerns | | Tetracycline | Moderate | Moderate | Moderate | Not preferred; poor intracellular penetration | | Azithromycin | Good | Low | Excellent | Emerging alternative (5 mg/kg/day × 3 days) | **Clinical Pearl:** In severe bacillary dysentery with dehydration, parenteral therapy (ceftriaxone IV) is preferred over oral agents to ensure adequate absorption and systemic control of infection. ### Why Other Options Fail - **TMP-SMX:** Resistance >50% in India; unreliable even as an alternative. - **Chloramphenicol:** Effective but associated with aplastic anemia and gray baby syndrome; reserved for life-threatening infections only. - **Tetracycline:** Moderate resistance; poor intracellular penetration compared to fluoroquinolones and cephalosporins. **Warning:** Do not assume older agents (ampicillin, TMP-SMX, tetracycline) are safe alternatives in endemic regions — resistance patterns have shifted dramatically over the past two decades.