Classification and Uses of Antiamoebic Drugs

• Luminal Amoebicides: Act on amoebae in the intestinal lumen. Examples: Paromomycin, Diloxanide furoate, Iodoquinol.
• Tissue Amoebicides: Target amoebae in tissues, especially the liver. Examples: Metronidazole, Tinidazole.
• Mixed Amoebicides: Effective in both the lumen and tissues. Examples: Metronidazole, Tinidazole.

Mechanism of Action

Directly toxic to amoebae in the intestinal lumen by disrupting membrane or enzyme function.

Therapeutic Uses

Used primarily to treat asymptomatic carriers of *E. histolytica* and prevent transmission. Often combined with tissue amoebicides for invasive amoebiasis.

Adverse Effects

• Paromomycin: GI upset, nephrotoxicity at high doses.
• Diloxanide furoate: GI symptoms like flatulence, nausea.
• Iodoquinol: Neurotoxicity (rare) and optic neuritis with prolonged use.

Contraindications

• Paromomycin: Severe renal impairment.
• Iodoquinol: Thyroid disease and prolonged use in children.

Mechanism of Action

Penetrate tissues to generate reactive metabolites that damage amoebic DNA and essential cellular proteins.

Therapeutic Uses

Used for acute amoebic dysentery, liver abscesses, and other invasive forms of amoebiasis. Effective against both intestinal and extraintestinal forms.

Adverse Effects

• Metronidazole: Metallic taste, nausea, headache, neuropathy, and disulfiram-like reaction with alcohol.
• Tinidazole: Similar to metronidazole, generally better tolerated.

Contraindications

• Metronidazole and Tinidazole: Avoid in first trimester of pregnancy and with alcohol.

Non-Antiamoebic Uses of Metronidazole

• Bacterial Infections: Anaerobic bacterial infections (e.g., *Bacteroides*, *Clostridium*).
• Clostridium difficile Infections: Treatment for mild to moderate *C. difficile* infections.
• Bacterial Vaginosis: First-line treatment for bacterial vaginosis caused by *Gardnerella vaginalis*.
• Giardiasis: Used against *Giardia lamblia* infections.
• Trichomoniasis: Treatment for *Trichomonas vaginalis* infections.
• Helicobacter pylori: Used in combination therapy for *H. pylori*-related peptic ulcers.

Mechanism of Action

Mixed amoebicides like metronidazole and tinidazole act in both the lumen and tissues by generating toxic metabolites that interact with amoebic DNA.

Therapeutic Uses

Effective for both invasive amoebiasis and symptomatic intestinal infections.

Adverse Effects

Same as tissue amoebicides, including metallic taste, GI upset, and neuropathy.

Contraindications

Should be avoided in the first trimester of pregnancy and with alcohol, similar to tissue amoebicides.