Rizatriptan

Rizatriptan is a fast-acting oral triptan used for acute treatment of migraine, available as tablets and orally disintegrating tablets. It has a similar efficacy to sumatriptan and the same vascular contraindications, and its dose is reduced with propranolol.

Mechanism. Serotonin 5-HT1B/1D receptor agonist that constricts cranial vessels and inhibits release of calcitonin gene-related peptide.

Pharmacokinetics. Bioavailability about 45% and half-life 2 to 3 hours. Peak is reached in 1 to 1.5 hours (about 1.6 to 2.5 hours for orally disintegrating tablets). It is metabolised by monoamine oxidase A. Propranolol raises levels by about 70%.

First-line use. Acute migraine attacks with or without aura.

• Oral rizatriptan: 10 mg at onset (5 mg if lower dose preferred). If migraine returns, repeat after at least 2 hours. Maximum 30 mg in 24 hours.

• With propranolol: 5 mg for each dose, maximum 15 mg in 24 hours.

• Children 6 to 17 years (where licensed): under 40 kg, 5 mg once; 40 kg and over, 10 mg once. Repeat doses are not studied.

Kidney, liver, weight and age.

• Kidney: no adjustment; use caution on dialysis.

• Liver: mild to moderate impairment, no adjustment; severe impairment not studied.

• Older adults: avoid over age 65 unless cardiovascular status is clear.

Contraindications. Ischaemic heart disease, previous myocardial infarction, coronary vasospasm, peripheral vascular disease, previous stroke or transient ischaemic attack, uncontrolled hypertension, hemiplegic or basilar migraine, monoamine oxidase A inhibitors within 2 weeks, and ergotamine or another triptan within 24 hours.

Serious adverse effects. Myocardial infarction, coronary vasospasm, arrhythmia, stroke, serotonin syndrome, angioedema, and medication overuse headache.

Common adverse effects. Dizziness, somnolence, fatigue, nausea, chest or throat tightness and paraesthesia.

Interactions. Propranolol (halve the dose), monoamine oxidase A inhibitors, ergot alkaloids and other triptans. Selective serotonin reuptake inhibitors and St John's wort add serotonin syndrome risk.

Common prescribing errors. Forgetting the propranolol dose reduction. Use on more than 10 days each month. Repeating doses within 2 hours.

Special groups.

• Pregnancy: fewer data than sumatriptan; avoid unless clearly needed.

• Breastfeeding: use with caution; milk transfer is low.

• Phenylketonuria: orally disintegrating tablets contain phenylalanine.

Formulations. Tablets 5 and 10 mg. Orally disintegrating tablets 5 and 10 mg, placed on the tongue and swallowed with saliva.

Monitoring.

• Baseline blood pressure and cardiovascular risk review.

• Headache diary, with acute treatment limited to under 10 days each month.

Stopping. No taper is needed.

Referral and escalation. Refer for poor response to two or more triptans, frequent attacks needing prevention, or suspected medication overuse headache.