Imitrex
Imitrex
Generic Name
Imitrex
Mechanism
- Selective 5‑HT₁B/1D receptor agonist – activates serotonin receptors on cranial arterial smooth muscle.
- Induces cerebral vasoconstriction – counteracts the vasodilation believed to drive migraine pain.
- Inhibits CGRP release – reduces neurogenic inflammation and neurovascular sensitization.
- Reduces trigeminal nerve activity – dampens central pain transmission in the brainstem.
Pharmacokinetics
| Parameter | Typical Value (oral 50 mg) |
| Absorption | Rapid; peak plasma concentration 1–3 h after dose |
| Bioavailability | ~50 % (food lowers by ~30 %) |
| Distribution | Widely distributed; efflux by P‑gp, limited CNS penetration at therapeutic doses |
| Metabolism | Primarily CYP‑2D6‑mediated; CYP‑2A6 also contributes |
| Elimination | Renal (≈33 %) and hepatic; t₁⁄₂ ≈ 2 h |
| Special Populations |
• CYP‑2D6 ultra‑rapid metabolizers: ↓ efficacy • renal impairment: minimal dose adjustment • hepatic impairment: not recommended |
Indications
- Acute treatment of migraine with or without aura in adults and adolescents (≥15 y).
- Attenuation of migraine severity and frequency when used on demand.
- Pre‑emptive therapy for certain headache disorders (e.g., cluster headaches in the off‑label setting).
Contraindications
| Contraindicated | Reason |
| Myocardial ischemia, unstable angina | Vasoconstriction may precipitate ischemia |
| Coronary artery disease or history of CV events | Restricts coronary perfusion |
| Uncontrolled hypertension | Excessive vasoconstriction |
| Severe hepatic or renal dysfunction | Altered clearance, risk of accumulation |
| Pregnancy (especially 1st trimester) | Potential fetal vasoconstriction |
| Duplicate triptan therapy | Additive vasoconstrictive risk |
| Severe peripheral vascular disease | Risk of ischemia |
| Patients on potent CYP‑2D6 inhibitors | Elevated plasma levels, augmented adverse effects |
Warnings
• Monitor for chest pain, palpitations, or sudden hypertension.
• Avoid in patients with prior CV disease, uncontrolled hypertension, or those on nitrates.
• Patients with a history of migraine aura may experience pro‑thrombotic risk.
Dosing
| Form | Dose | Timing | Notes |
| Oral | 50 mg single dose | As soon as migraine pain begins | Can repeat 2× after 2 h if pain persists |
| On‑Demand Dose | 25 mg (for mild cases) | ± 30 min after first dose | Consider age and weight; Drug‑Drug Interactions:
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• Potentiates effects of MAO inhibitors → contraindicated.
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• Co‑administer with verapamil (CYP‑2D6 inhibitor) → ↑ risk of CV adverse events.
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• Cyclobenzaprine, tramadol, or other serotonergic agents may add serotonin‑synergy risk.
Adverse Effects
- Common (≤10 %)
- Flushing, tingling, hot‑flush sensations
- Dizziness, headache, fatigue
- Nausea, abdominal discomfort
- Palpitations, mild hypertension
- Serious (≤1 %)
- Cardiac ischemia (chest pain, arrhythmias)
- Hypertension, uncontrolled BP spikes
- Cerebrovascular events (stroke, TIA)
- Severe allergic reactions (angioedema, anaphylaxis)
- Liver enzyme elevations (rare)
> Safety Monitoring
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• Baseline and follow‑up blood pressure checks
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• ECG in patients >40 y or with CV risk factors
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• Liver function tests when high‑dose or chronic use is anticipated
Monitoring
- Vital signs: BP, HR before and 30 min after dose.
- Cardiac rhythm: 12‑lead ECG for patients ≥40 y or with concurrent cardiovascular medication.
- Drug interactions: Review concurrent serotonergic drugs.
- Adverse effect reporting: Document any chest pain or abnormal BP readings.
Clinical Pearls
| Pearl | Practical Take‑away |
| Peptide vs. Triptan | Imitrex is a synthetic serotonin analogue – easy to remember its vasoconstrictive action targets both systemic vessels and cranial arteries. |
| Early‑onset is Key | Use as soon as the migraine aura or pain begins; leverages short half‑life and rapid onset for best efficacy. |
| Avoid Duplication | A single dose patient should not redirect for second or third triptan doses without physician’s approval; risk of CV side effects increases. |
| Food Interaction | Skip breakfast or a heavy meal for 30 min after dosing; food slows absorption and reduces peak concentrations. |
| Age Adjustments | In children <12 y, use cautiously; the pharmacodynamics differ and safety data are limited. |
| CYP‑2D6 Ultra‑Rapid Metabolizers | They metabolize sumatriptan quickly → sub‑therapeutic, consider alternatives such as frovatriptan or gepants. |
| Prenatal Use | Not recommended, but if necessary, discuss risk/benefit with obstetrician; use lowest effective dose. |
| Non‑responsive Migraines | If no relief after two doses, consider a different class (gepants, ditans) and reassess migraine diagnosis. |
*Ensure patient education on signs of cardiac ischemia; a quick phone call and immediate care can reduce morbidity.*