Dysentery medication

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Here is a comprehensive overview of dysentery medications, covering the two main types — bacillary dysentery (Shigella) and amebic dysentery — based on authoritative medical textbooks.

Dysentery: Overview of Treatment

1. Bacillary Dysentery (Shigellosis)

Caused by Shigella species, including S. dysenteriae type 1 (the most severe).

General principles:

Mild, uncomplicated cases in high-income settings may be self-limiting and require no antibiotic treatment
Oral rehydration (with zinc sulfate 20 mg) is the cornerstone of supportive care
Antimotility agents (e.g., loperamide) are contraindicated — they prolong symptoms and bacterial shedding
Antibiotics are routinely recommended for dysentery (bloody diarrhea with fever), severe illness, immunocompromised patients, and during outbreaks

Antibiotic regimens (WHO-recommended):

Drug	Children	Adults	Notes
Ciprofloxacin (first-line)	15 mg/kg twice daily × 3 days PO	500 mg once daily × 3 days PO	Fluoroquinolone of choice
Ceftriaxone (severe/IV)	50–100 mg/kg once daily × 2–5 days IV/IM	1 g every 24 h × 3 days IV/IM	For vomiting, unconsciousness, or severe illness
Azithromycin (if cipro-resistant)	6–20 mg/kg once daily × 1–5 days PO	500 mg twice daily × 1 day (or 1–1.5 g)	Risk of resistance emergence
Pivmecillinam (second-line)	20 mg/kg 4×/day × 5 days PO	100 mg 4×/day × 5 days	Limited by frequent dosing and cost
TMP-SMX (where susceptible)	—	160/800 mg twice daily × 5 days	Resistance increasingly common
Cefixime (oral alternative)	—	400 mg once daily × 3 days	For cipro-resistant strains

Duration notes:

Non-dysenteriae Shigella in immunocompetent adults: 3 days
S. dysenteriae type 1: 5 days
Immunocompromised patients: 7–10 days

— Goldman-Cecil Medicine, Harrison's Principles of Internal Medicine 22E

2. Amebic Dysentery (Entamoeba histolytica)

Treatment of choice: Metronidazole + a luminal amebicide

Tissue/Invasive Amebicides (treat colitis and systemic disease)

Drug	Role	Notes
Metronidazole	First-line; kills trophozoites	500–750 mg three times daily × 7–10 days; does NOT kill cysts
Tinidazole	Alternative to metronidazole	Simpler dosing, better tolerability; same mechanism
Tetracyclines	Alternative for moderate colitis only	Not effective against extraintestinal disease
Erythromycin	Alternative for moderate colitis only	Not effective against extraintestinal disease

Mechanism of metronidazole/tinidazole: The nitro group is chemically reduced in anaerobic organisms, generating reactive products responsible for antiprotozoal activity. Both drugs are well absorbed orally, with low protein binding; metronidazole half-life ~7.5 h, tinidazole ~12–14 h.

Luminal Amebicides (must always be added to eradicate cysts in the gut)

Drug	Efficacy
Diloxanide furoate	~80–90% eradication of carriage
Iodoquinol	~80–90% eradication of carriage
Paromomycin	~80–90% eradication of carriage

Important: Even after successful treatment of invasive disease with metronidazole, a luminal amebicide must be added — metronidazole and tinidazole do not reliably eliminate luminal cysts.

— Goldman-Cecil Medicine, Katzung's Basic and Clinical Pharmacology 16th Ed.

3. Other Causes of Dysentery-Like Illness

Organism	Treatment
Trichuris trichiura (whipworm)	Mebendazole, albendazole, or ivermectin
Balantioides coli	Tetracycline or metronidazole
EIEC (E. coli invasive)	Supportive; antibiotics generally not recommended (risk of HUS)

Key Clinical Pearls

Resistance is rising for Shigella — always use local susceptibility data when available
Do not use antimotility agents in dysentery
Zinc supplementation (20 mg/day × 10–14 days) reduces duration of shigellosis in children in resource-limited settings
For amebic liver abscess (complication of amebic dysentery): metronidazole × 10 days cures >95% of uncomplicated cases; if metronidazole fails, add chloroquine and consider abscess aspiration

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