Sumatriptan
A medication used for the treatment of migraine headaches. Efficacty is increased with earlier administration.
Clinical Data
| Trade names | Imitrex, Imigran,Treximet |
| Pregnancy category | C |
| Routes | tablet, subcutaneous injection, nasal spray, transdermal electrophoresis |
Mechanism of action
Sumatriptan is structurally similar to serotonin (5HT), and is a 5-HT receptor (types 5-HT1D and 5-HT1B) 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, it is presumed, accounts for sumatriptan's efficacy in treating cluster headaches. The injectable form of the drug has been shown to abort a cluster headache within fifteen minutes in 96% of cases.
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 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.
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.