Erenumab

Pain / Migraine Prevention

Also known as: Aimovig

Anti-CGRP AntibodiesResearch phase: Extensive human data (post-marketing)Regulatory: FDA-approved (2018). First-in-class CGRP pathway treatment for migraine prevention. Aimovig (Amgen/Novartis). 70mg or 140mg SC monthly.

Mechanism

The first FDA-approved treatment that specifically targets the CGRP migraine pathway. Unlike the other anti-CGRP antibodies that block the CGRP molecule floating in blood, erenumab blocks the CGRP receptor itself — like putting a lock on the door rather than catching the key. Given as a monthly self-injection, it reduces migraine days by about 3-4 per month with minimal side effects.

Technical detail

Fully human IgG2 monoclonal antibody (150 kDa) that binds the canonical CGRP receptor (CLR/RAMP1 heterodimer) with high affinity (KD ~20 pM). Unique mechanism among anti-CGRP therapies: targets the receptor, not the ligand. Blocks both alpha-CGRP and beta-CGRP signaling at the receptor. CGRP receptor is expressed on trigeminal ganglion neurons, meningeal vasculature, and brainstem nuclei involved in migraine pathophysiology. Does not cross blood-brain barrier — peripheral mechanism of action. Phase 3 STRIVE trial (episodic migraine, n=955): 140mg dose reduced monthly migraine days by 3.7 vs. 1.8 for placebo. Phase 3 data for chronic migraine: 2.5 additional days reduction vs. placebo. Half-life ~28 days. Constipation is most common side effect (3-4%), related to CGRP's role in gut motility. No hepatotoxicity concerns (unlike small molecule CGRP antagonists).

Effects

NERVOUS SYSTEM (MIGRAINE): Erenumab (Aimovig) is a fully human monoclonal antibody that blocks the calcitonin gene-related peptide receptor (CGRP-R) — notably, it is the ONLY CGRP therapy that targets the receptor rather than the CGRP ligand, making it mechanistically unique in the class [pharmacological]. CGRP is a 37-amino-acid neuropeptide released from trigeminal sensory neurons during migraine attacks, causing potent vasodilation, neurogenic inflammation, and pain signal transmission in the trigeminovascular system [established neurobiology]. By blocking the CGRP receptor on vascular smooth muscle, trigeminal neurons, and brainstem nuclei, erenumab prevents CGRP signaling without depleting the peptide itself [pharmacological]. MIGRAINE PREVENTION: In episodic migraine (4-14 days/month), erenumab reduces monthly migraine days by 3-4 days vs. 1-2 days placebo (STRIVE: -3.2 days at 70mg, -3.7 at 140mg vs. -1.8 placebo) [RCT — Goadsby et al., 2017, NEJM]. In chronic migraine (≥15 days/month), ARISE trial showed -2.9 days vs. -1.8 placebo [RCT]. 50% responder rate (proportion achieving ≥50% reduction in migraine days): 43-50% at 70mg, 50% at 140mg (vs. ~27% placebo) [RCT]. Benefits begin within the first month — faster onset than traditional oral preventives (topiramate, valproate require 2-3 months) [clinical observation]. CARDIOVASCULAR: CGRP is a potent vasodilator and plays roles in cardiovascular homeostasis. Blocking CGRP-R theoretically could affect blood pressure regulation, wound healing, and cardiac protection during ischemia. Clinical data shows no significant blood pressure changes or increased CV events, though long-term (>5 year) CV safety data is still accumulating [RCT, post-market]. GASTROINTESTINAL: Constipation is the most notable side effect — occurs in 1-3% of patients (higher in clinical practice reports, up to 5-10%). Mechanism: CGRP promotes GI motility; blocking its receptor reduces peristalsis [clinical, pharmacological]. Rarely severe — can lead to hospitalization for constipation with complications [post-marketing reports]. MUSCULOSKELETAL: Muscle spasm and cramp reports in post-marketing surveillance — mechanism unclear, possibly related to CGRP's role in muscle blood flow [post-marketing].

Practitioner Guide

ADMINISTRATION: Subcutaneous injection, monthly. Available as 70mg and 140mg single-dose autoinjectors (SureClick) or prefilled syringes. Self-administered by patients at home. Inject in abdomen, thigh, or upper arm. Room temperature for 30 minutes before injection (reduces injection site pain). DOSING: Start at 70mg SC monthly. If inadequate response after 3 months, increase to 140mg monthly (two 70mg injections). Some patients respond well at 70mg — no need to escalate if controlled. Allow 3 monthly doses before assessing efficacy (some patients respond by month 1, but full benefit may take 3 months). UNIQUE RECEPTOR-TARGETING MECHANISM: Unlike fremanezumab and galcanezumab (which bind CGRP ligand), erenumab blocks the CGRP receptor. Clinical implications: (1) no theoretical concern about forming immune complexes with circulating CGRP, (2) may provide more complete receptor blockade since it prevents any CGRP (α and β) from binding, (3) if a patient fails ligand-targeting antibodies, erenumab may still work (and vice versa) — switching within the class is reasonable. CONSTIPATION MANAGEMENT: Proactive counseling at initiation — increase fiber (25-35g/day), adequate hydration (2-3L/day), regular exercise. If constipation develops: first-line polyethylene glycol (MiraLAX) 17g daily. Second-line: add senna or bisacodyl. If severe or persistent: consider switching to a ligand-targeting anti-CGRP (fremanezumab or galcanezumab) which may have lower constipation rates (receptor blockade may cause more GI effects than ligand sequestration). PATIENT SELECTION: Best candidates: episodic or chronic migraine patients who have failed or cannot tolerate 2+ oral preventives (topiramate, propranolol, amitriptyline, valproate). Patients with medication overuse headache. Patients who prefer monthly injection over daily pills. Patients with comorbidities that limit oral preventive options (e.g., depression limiting topiramate, asthma limiting beta-blockers). SWITCHING WITHIN CGRP CLASS: If erenumab fails after 3-month trial, switch to a ligand-targeting antibody (different mechanism — may capture a different patient population). Response to one CGRP therapy does not guarantee response to another. COMBINATION: Can combine with oral preventives (topiramate, propranolol) for refractory patients. Can use with triptans for acute treatment (triptans work on 5-HT1B/1D, different from CGRP pathway). INSURANCE/ACCESS: Prior authorization typically required — document failure of 2+ oral preventives. Manufacturer copay programs available. Cost approximately $600-700/month without insurance. STORAGE: Refrigerate (2-8°C). Can store at room temperature (up to 25°C) for up to 7 days. Protect from light.

Evidence

Research Summary

TIER 1: STRIVE (Goadsby et al., 2017 — NEJM): Phase 3 RCT in episodic migraine — erenumab 70mg and 140mg reduced monthly migraine days by 3.2 and 3.7 (vs. 1.8 placebo) over 6 months. 50% responder rate: 43% and 50% (vs. 27%). ARISE (Dodick et al., 2018): Phase 3 in episodic migraine — erenumab 70mg, -2.9 days vs. -1.8 placebo. Phase 2 chronic migraine trial (Tepper et al., 2017): significant reduction in monthly migraine days. LIBERTY (Reuter et al., 2018): erenumab in patients who failed 2-4 prior preventives — 30% achieved 50% response (vs. 14% placebo), demonstrating efficacy in treatment-resistant patients. FDA approved May 2018 — first FDA-approved CGRP therapy. Open-label extension studies: sustained efficacy over 4+ years without tolerance. TIER 2: Systematic reviews and meta-analyses of CGRP monoclonal antibodies (Deng et al., 2020; Xu et al., 2019) — all four agents effective, no clear superiority of one over another. Network meta-analyses comparing CGRP antibodies to oral preventives. Post-marketing safety analyses confirming cardiovascular safety. Expert consensus guidelines (AHS, EHF) recommending CGRP antibodies after failure of oral preventives. TIER 3: Real-world effectiveness studies from headache center registries. Case reports of severe constipation and related complications. Practitioner switching protocols within the CGRP class. Patient-reported outcomes data from specialty headache clinics. KEY FINDINGS: Erenumab opened the era of CGRP-targeted migraine prevention — the first mechanism-specific preventive therapy for migraine. Its receptor-targeting approach is unique in the class. Efficacy is consistent and durable, onset is faster than oral preventives, and the safety profile is favorable. Constipation is the main differentiating side effect vs. ligand-targeting antibodies. GAPS: Long-term cardiovascular safety (>10 years). Optimal duration of treatment (when to stop — some patients maintain remission after discontinuation). Head-to-head trials vs. other CGRP antibodies limited. Biomarkers to predict response not identified. ACTIVE TRIALS: Erenumab in medication overuse headache, post-traumatic headache, cluster headache. Comparative effectiveness studies vs. other CGRP therapies. Studies of CGRP antibody withdrawal and relapse patterns.

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