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Mechanism of action
Sumatriptan is molecularly similar to serotonin (5-HT), and is a 5-HT receptor (types 5-HT1D and 5-HT1B ) agonist. Sumatriptan's primary therapeutic effect is related in its inhibition of the release of Calcitonin gene-related peptide (CGRP), likely through its 5-HT1D/1B receptor-agonist action. This has been substantiated by the efficacy of more recently developed CGRP targeting drugs and antibodies developed for the preventive treatment of migraine. How agonism of the 5-HT1D/1B receptors inhibits CGRP release is not fully understood. CGRP is believed to cause sensitization of trigeminal nociceptive neurons, contributing to the pain experienced in migraine.

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 30 minutes in 77% of cases.

Pharmacokinetics
Sumatriptan is administered in several forms: tablets, subcutaneous injection, and nasal spray. Oral administration (as succinate salt) has low bioavailability, partly due to presystemic metabolism—some of it gets broken down in the stomach and bloodstream before it reaches the target arteries. A rapid-release tablet formulation with the same bioavailability but a high concentration can achieve therapeutic effects on average 10–15 minutes earlier than other oral forumulations. 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 2-{5-[(methylsulfamoyl)methyl]-indole-3-yl}acetic acid, which is then conjugated to 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.

Interactions
Concurrent use with other triptans or ergot-containing medications within 24 hours can result in additive vasoconstriction. Increased systemic exposure to sumatriptan can occur if used within 2 weeks after a monoamine oxidase inhibitor. Cases of serotonin syndrome have been reported with co-administration of triptans and serotonin reuptake inhibitors.