All of the following are true regarding sumatriptan except: September 2009
Ans. A: 99% oral bioavailability Sumatriptan is structurally similar to serotonin, and is a selective 5-HT 1B/1D receptor agonist. The specific receptor subtypes it activates are present on the cranial aeries and veins. Acting as an agonist at these receptors, Sumatriptan reduces the vascular inflammation associated with migraine. It causes constriction of dilated cranial extracerebral blood vessels, especially the aerio-venous shunts in the carotid aery. Dilatation of these shunt vessels during migraine attack is believed to dive blood flow away from the brain parenchyma. Sumatriptan is administered in several forms; tablets, subcutaneous injection, and nasal spray. Oral administration (as succinate) suffers from poor bioavailability, paly due to presystemic metabolism -- some of it gets broken down in the stomach and bloodstream before it reaches the target aeries. Sumatriptan is metabolised primarily by monoamine oxidase A into an indole acetic acid analogue, pa of which is fuher conjugated with glucuronic acid. These metabolites are excreted in the urine and bile. Large doses of sumatriptan (200 mg/ day) 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. Serious cardiac events include coronary aery vasospasm, transient myocardial ischemia, myocardial infarction, ventricular tachycardia, and ventricular fibrillation.
99% oral bioavailability
Contraindicated in coronary aery disease
Constricts cranial vessels
Selective 5-HT 1B/1D receptor agonist