umatriptan

Sumatriptan (Imitrex, Imigran,Imigran Recovery ) is a triptan drug including a sulfonamide group which was originally developed by Glaxo for the treatment of migraine headaches.

Approval and availability

Several dosage forms for sumatriptan have been approved, including tablets, solution for injection, and nasal inhalers. Sumatriptan was the first triptan available (in 1991), and, in the United States and most developed countries, is available only by medical prescription. In the United Kingdom, sumatriptan is available over the counter, under the name of Imigran Recovery. It is sold in packs of two 50mg tablets for approximately £7.99 (about $15 US). Larger pack sizes, the nasal spray, and the liquid preparation for injection are still only available by prescription. Originally covered by UK Patent GB2162522, extended by supplementary protection certificate SPC/GB93/071, protection in the UK (as well as the rest of Europe) has now expired, as of 16 May 2006. However, cheaper generic versions are as yet only available via prescription.

Mode of action

Oftentimes, serotonin levels in the brain become extremely erratic before the onset of a migraine. In an attempt to stabilize this, sumatriptan is administered to help aid in leveling the serotonin levels in the brain. Sumatriptan is structurally similar to serotonin, and is a 5-HT (5-HT1D) agonist, which is one of the receptors that serotonin binds to. The specific receptor subtype it activates is present in the cranial and basilar arteries. Activation of these receptors causes vasoconstriction of those dilated arteries. Sumatriptan is also shown to decrease the activity of the trigeminal nerve.

Pharmacokinetics

Sumatriptan is administered in several forms; tablets, subcutaneous injection, and nasal spray. Oral administration (as succinate) suffers from poor bioavailability, partly due to presystemic metabolism — some of it gets broken down in the stomach and bloodstream before it reaches the target arteries. A new rapid-release tablet formulation has the same bioavailability, but the maximum concentration is achieved on average 10-15 minutes earlier. When injected, sumatriptan is faster acting (usually within a minute), but the effect lasts for a shorter time. Sumatriptan is metabolised primarily by monoamine oxidase A into an indole acetic acid analogue, part of which is further conjugated with glucuronic acid. These metabolites are excreted in the urine and bile.

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