What is the best alternative treatment for a patient with chronic migraine (CM) and irritable bowel syndrome (IBS) who is experiencing constipation while on erenumab (aimovig)

Management of Constipation in a Patient with Chronic Migraine on Erenumab

The best recommendation for this patient is to change erenumab to fremanezumab 225 mg monthly to maintain migraine control while reducing constipation side effects.

Rationale for Switching to Fremanezumab

Erenumab (Aimovig) is associated with constipation as a known side effect, which is particularly problematic in this patient with pre-existing irritable bowel syndrome (IBS). The 2024 VA/DoD Clinical Practice Guideline for Headache Management strongly recommends CGRP monoclonal antibodies including fremanezumab for chronic migraine prevention with a "strong for" recommendation 1.

While erenumab has been effective for this patient (75% reduction in monthly migraine days), the severe constipation (5-7 days without bowel movements) represents an unacceptable side effect that is compromising her quality of life and potentially worsening her IBS.

Comparison of CGRP Antagonist Options

Fremanezumab (Recommended Option)

• Targets the CGRP ligand rather than the receptor (unlike erenumab)
• Has a "strong for" recommendation in the 2024 VA/DoD guidelines 1
• Does not have the same association with constipation as erenumab
• Monthly dosing maintains the same convenient administration schedule

Erenumab Dose Reduction (Not Recommended)

• Reducing to 70 mg would likely maintain some efficacy but may not eliminate constipation
• Long-term efficacy data shows numerically greater reductions in monthly migraine days with 140 mg vs 70 mg 2
• Constipation is a dose-dependent side effect that would likely persist even at lower doses

Atogepant (Not Recommended)

• Daily oral dosing is less convenient than monthly injection
• Has only a "weak for" recommendation for episodic migraine prevention in the VA/DoD guidelines 1
• May still cause gastrointestinal side effects

Rimegepant (Not Recommended)

• Every-other-day dosing is less convenient than monthly injection
• Has a "neither for nor against" recommendation for episodic migraine prevention in the VA/DoD guidelines 1
• Limited evidence for chronic migraine prevention

Management of Constipation

While switching to fremanezumab, the patient's constipation should be addressed with:

1. Dietary modifications:

   • Increase soluble fiber intake
   • Ensure adequate hydration
   • Consider a low-FODMAP diet under dietitian supervision 3

2. Pharmacological management:

   • Osmotic laxatives like polyethylene glycol
   • Consider linaclotide 290 mcg once daily if needed (strong recommendation, high-quality evidence) 1
   • Avoid bulk-forming laxatives that may worsen bloating in IBS 1

Follow-up Recommendations

• Reassess migraine control and bowel function 4-6 weeks after switching to fremanezumab
• Monitor for any new side effects
• Continue to optimize bowel regimen as needed
• If constipation persists despite medication change, consider gastroenterology referral for specialized IBS management

Conclusion

Switching to fremanezumab 225 mg monthly offers the best balance of maintaining excellent migraine control while eliminating the constipation side effect that is severely affecting this patient's quality of life. This approach is supported by the strongest and most recent clinical guidelines for migraine management 1 and addresses both the neurological and gastrointestinal aspects of the patient's condition.