SUMATRIPTAN - CLINICAL PHARMACOKINETICS

Sumatriptan is a novel serotonin(1) (5-hydroxytryptamine(1); 5-HT1)-like agonist which has been shown to be effective in the treatment of acute migraine. Single-dose pharmacokinetic studies reflect the way that sumatriptan will be used in routine practice, but relatively few studies have been published. Bioavailability is high (96%) following subcutaneous injection, but low (14%) following oral administration because of first-pass metabolism. Absorption is rapid after subcutaneous injection, with peak concentration reached in 10 minutes. After oral administration, multiple peak concentrations are observed, but a concentration that is 75% of the final peak concentration is usually reached within 45 minutes. Less than 20% of the drug is protein bound. The volume of distribution is greater than total body water at 170L. Total plasma clearance is rapid, with an elimination half-life of around 2 hours. There is one major metabolite (an indole acetic acid analogue) which is excreted in the urine as the free acid and its ester glucuronide conjugate. The pharmacokinetic profile of sumatriptan is not significantly affected by an acute migraine attack (absorption phase), old age or gender. Pharmacokinetic studies in individuals with hepatic and renal disease have not been published; however, care should be taken when sumatriptan is administered to patients with liver disease until such information is available. No significant interaction was found between sumatriptan and propranolol, flunarizine, pizotifen or alcohol (ethanol).