What is the recommended dose of Metamucil (psyllium) for treating diarrhea?

Metamucil Dosing for Diarrhea

Metamucil (psyllium) is not recommended as a primary treatment for acute diarrhea; loperamide is the preferred first-line agent at 4 mg initially, followed by 2 mg after each loose stool (maximum 16 mg/day). 1

Primary Treatment Approach

The evidence-based guidelines consistently prioritize loperamide over fiber supplementation for diarrhea management:

• Loperamide dosing: Start with 4 mg, then 2 mg every 2-4 hours or after each unformed stool, not exceeding 16 mg daily 1
• Oral rehydration therapy is appropriate for mild diarrhea alongside symptomatic treatment 1
• Dietary modifications including reduction of insoluble fiber intake may be useful 1

When Psyllium May Be Considered

While major clinical guidelines do not recommend psyllium for acute diarrhea treatment, the FDA-approved dosing for psyllium when used is:

• Adults and children ≥12 years: 1 packet (approximately 3.4g psyllium) in 8 oz liquid at first sign of irregularity, up to 3 times daily 2
• Children 6-11 years: ½ packet in 8 oz liquid, up to 3 times daily 2
• Start low and titrate: Begin with 1 dose per day, gradually increase to 3 doses daily as needed 2

Limited Evidence Context

Research supporting psyllium for diarrhea is limited to specific scenarios:

• Radiation-induced diarrhea: One pilot study showed psyllium significantly decreased incidence (p=0.049) and severity (p=0.030) of radiation-induced diarrhea 3
• Experimental secretory diarrhea: Psyllium improved fecal consistency and viscosity in phenolphthalein-induced diarrhea, while other fiber types did not 4
• Chronic large-bowel diarrhea: Veterinary studies suggest benefit in chronic conditions, not acute diarrhea 5, 6

Critical Clinical Caveats

Important warnings when considering fiber for diarrhea:

• Guidelines specifically recommend reduction of insoluble fiber intake during acute diarrhea 1
• Psyllium requires adequate fluid intake (at least 8 oz per dose) to prevent obstruction 2
• Never use fiber as monotherapy for moderate-to-severe diarrhea, bloody diarrhea, or diarrhea with fever 1
• If diarrhea persists beyond 24-48 hours on loperamide, escalate to second-line agents (octreotide, antibiotics) rather than adding fiber 1

Algorithmic Approach

1. Mild uncomplicated diarrhea: Loperamide 4 mg initially, then 2 mg after each loose stool (max 16 mg/day) + oral rehydration 1
2. If persists >24 hours: Increase loperamide to 2 mg every 2 hours + consider antibiotics 1
3. If persists >48 hours: Discontinue loperamide, start octreotide 100-150 mcg subcutaneously three times daily 1
4. Complicated diarrhea (fever, dehydration, bloody stools): Hospitalize, IV fluids, octreotide, antibiotics 1

Psyllium has no established role in this evidence-based algorithm for acute diarrhea management.