Sumatriptan

Medical uses

Sumatriptan is effective for ending or relieving the intensity of migraine and cluster headaches. It is most effective taken early after the start of the pain. Injected sumatriptan is more effective than other formulations.

Adverse effects

Large doses of sumatriptan can cause sulfhemoglobinemia, a rare condition in which the blood changes from red to greenish-black, due to the integration of sulfur into the hemoglobin molecule. If sumatriptan is discontinued, the condition reverses within a few weeks.

Serious cardiac events, including some that have been fatal, have occurred following the use of sumatriptan injection or tablets. Events reported have included coronary artery vasospasm, transient myocardial ischemia, myocardial infarction, ventricular tachycardia, and ventricular fibrillation (V-Fib).

The most common side effects reported by at least 2% of patients in controlled trials of sumatriptan (25-, 50-, and 100-mg tablets) for migraine are atypical sensations (paresthesias and warm/cold sensations) reported by 4% in the placebo group and 5–6% in the sumatriptan groups, pain and other pressure sensations (including chest pain) reported by 4% in the placebo group and 6–8% in the sumatriptan groups, neurological events (vertigo) reported by less than 1% in the placebo group and less than 1% to 2% in the sumatriptan groups. Malaise/fatigue occurred in less than 1% of the placebo group and 2–3% of the sumatriptan groups. Sleep disturbance occurred in less than 1% in the placebo group to 2% in the sumatriptan group.

Mechanism of action

Sumatriptan is structurally similar to serotonin (5-HT), and is a 5-HT receptor (types 5-HT_1D and 5-HT_1B) agonist. The specific receptor subtypes it activates are present on the cranial arteries and veins. Acting as an agonist at these receptors, sumatriptan reduces the vascular inflammation associated with migraines.

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, which presumably accounts for sumatriptan's efficacy in treating cluster headaches. The injectable form of the drug has been shown to abort a cluster headache within 15 minutes in 96% of cases.

Pharmacokinetics

Sumatriptan is administered in several forms: tablets, subcutaneous injection, and nasal spray. Oral administration (as a 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 10 minutes), 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. Only about 3% of the active drug may be recovered unchanged.

There is no simple, direct relationship between sumatriptan concentration (pharmacokinetics) per se in the blood and its anti-migraine effect (pharmacodynamics). This paradox has, to some extent, been resolved by comparing the rates of absorption of the various sumatriptan formulations, rather than the absolute amounts of drug that they deliver.

Approval

Sumatriptan was the first clinically available triptan (in 1991). In the United States, it is available only by medical prescription (and is frequently limited, without prior authorization, to a quantity of nine in a 30-day period). However, it can be bought over the counter in the UK and Sweden. Several dosage forms for sumatriptan have been approved, including tablets, solution for injection, and nasal inhalers.

On April 15, 2008, the US FDA approved Treximet, a combination of sumatriptan and naproxen, an NSAID. This combination has shown a benefit over either medicine used separately.

In July 2009, the US FDA approved a single-use jet injector formulation of sumatriptan. The device delivers a subcutaneous injection of 6 mg sumatriptan, without the use of a needle. Autoinjectors with needles have been previously available in Europe and North America for several years.

Phase III studies with a iontophoretic transdermal patch (Zelrix/Zecuity) started in July 2008. This patch uses low voltage controlled by a pre-programmed microchip to deliver a single dose of sumatriptan through the skin within 30 minutes. Zecuity was approved by the US FDA in January 2013.

Generics

On November 6, 2008, Par Pharmaceutical announced that it would begin shipping generic versions of sumatriptan injection (sumatriptan succinate injection) 4- and 6-mg starter kits and 4- and 6-mg filled syringe cartridges to the trade immediately. In addition, Par anticipates launching the 6-mg vials early in 2009.

Mylan Laboratories Inc., Ranbaxy Laboratories, Sandoz (a subsidiary of Novartis), Dr. Reddy's Laboratories, and other companies have received FDA approval for generic versions of sumatriptan tablets in 25-, 50-, and 100-mg doses since 2009. The drug is generically available in U.S. and European markets, since Glaxo's patent protections have expired in those jurisdictions. Nasal spray sumatriptan is also generically available.