Is Reglan (metoclopramide) used to treat constipation?

Metoclopramide (Reglan) for Constipation

Metoclopramide is not primarily indicated for constipation and should only be considered in specific circumstances such as gastroparesis-related constipation or when constipation is associated with delayed gastric emptying. 1

Mechanism and Effects on Gastrointestinal Motility

Metoclopramide works as a dopamine receptor antagonist with the following effects:

• Increases upper gastrointestinal tract motility
• Stimulates gastric emptying and intestinal transit
• Increases tone and amplitude of gastric contractions
• Relaxes the pyloric sphincter and duodenal bulb
• Increases peristalsis of the duodenum and jejunum 2

Importantly, metoclopramide has little to no effect on colonic motility, which is the primary area of concern in most cases of constipation. 2

Appropriate Clinical Uses

Metoclopramide may be considered in constipation only when:

1. Gastroparesis is suspected: Particularly in diabetic patients where delayed gastric emptying contributes to constipation 3
2. When constipation is accompanied by nausea and vomiting: Due to its antiemetic properties 1
3. In specific cases of small intestinal dysmotility: When other treatments have failed 1

Safety Concerns and Limitations

The European Medicines Agency's Committee recommends against long-term use of metoclopramide due to:

• Risk of extrapyramidal side effects (especially in children)
• Potentially irreversible tardive dyskinesia in elderly patients
• Lack of consistent benefit in gastroparesis 1

Additional concerns include:

• Sedation
• QT interval prolongation
• Increased prolactin levels 2, 4

Preferred First-Line Treatments for Constipation

For most cases of constipation, the following treatments are recommended instead:

1. Osmotic laxatives: Polyethylene glycol (17-34g daily), lactulose, or magnesium hydroxide 5
2. Stimulant laxatives: Bisacodyl (10-15 mg, 2-3 times daily) or senna (2-3 tablets twice daily) 5
3. For opioid-induced constipation: Methylnaltrexone (0.15 mg/kg subcutaneously every other day) or naloxegol 1, 5

Special Circumstances

In diabetic patients with constipation:

• Stool softeners combined with metoclopramide may be helpful when there is evidence of impaired gastric emptying 3
• However, this should only be considered after first-line treatments have failed

In patients with vincristine-induced ileus:

• Metoclopramide has been reported as effective after ruling out bowel obstruction 6
• This represents a very specific clinical scenario and not general constipation management

Clinical Decision Algorithm

1. Assess for the cause of constipation
2. For typical constipation:
   • Start with osmotic laxatives
   • Add stimulant laxatives if needed
   • Consider specialized agents for opioid-induced constipation
3. Only consider metoclopramide if:
   • There is confirmed gastroparesis or upper GI dysmotility
   • First-line treatments have failed
   • The patient has no contraindications (elderly, risk of movement disorders)
   • Short-term use is planned

Conclusion

While metoclopramide has prokinetic effects on the upper gastrointestinal tract, it is not a first-line or even typical treatment for constipation due to its limited effect on colonic motility and significant side effect profile. Other agents with better safety profiles and more targeted colonic effects should be used first.