Antidiarrheal Drugs

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Classification:

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Acute: less than 2 weeks. often caused by infectious agent thus treated with antibiotics. In the initial stage motility-decreasing drugs should not be used since they interfere with bacterial excretion. Fluid & electrolyte balance should be the treatment.

Subacute: 2-4 weeks

Chronic: > 4 weeks. treated by anti-diarrheal agents. treatment is based on underlying cause: can be motility-based, osmotic diarrhea, secretory diarrhea, inflammatory diarrhea (IBD)

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Anti-motility agents

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Opioid derivatives: morphine, codeine, papaverine

morphine: activates cascade in myenteric & submucosal plexuses causing opening of K channels & hyperpolarization of enteric neurons: it inhibits ACh release. also sphincter constriction: spastic constipation.

papaverine: PDE inhibitor: SMC relaxation. causes paralytic constipation

Opium: contains both morphine and papaverine

2 synthetic morphine analogs
- Laperamide (imodium): dont cross BBB
- Diphenoxylate: crosses BBB
they are often combined with atropine. may cause toxic megacolon.

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Agents that modify fluid and electrolyte transport

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- NSAIDs: probably due to PG inhibition
- Bismuth subsalicylate:

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Anti-spasmodic agents

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useful in irritable bowel disease
- propantheline: muscarinic R antagonist
- Dicycloverine: muscarininc R antagonist

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Adsorbents

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Methylcellulose, Kaolin, Chancoal

they absorb intestinal toxins or microorganisms from solutions. less effective than antimotility agents.