Selective 5–HT1B/1D receptor agonist useful in acute migraine is :
**Core Concept**
The question is testing knowledge of a specific class of medications used in the management of acute migraine. 5-HT1B/1D receptor agonists, also known as triptans, are a group of drugs that act by stimulating serotonin receptors to constrict blood vessels and block pain pathways in the brain.
**Why the Correct Answer is Right**
The correct answer, **Rizatriptan**, is a selective 5-HT1B/1D receptor agonist that is specifically used in the treatment of acute migraine attacks. It works by binding to the 5-HT1B and 5-HT1D receptors in the brain, causing vasoconstriction of the intracranial blood vessels and inhibiting the release of pro-inflammatory neuropeptides that contribute to pain transmission. This mechanism of action is responsible for its efficacy in relieving migraine headache.
**Why Each Wrong Option is Incorrect**
**Option A:** **Frovatriptan** - While Frovatriptan is also a triptan, it has a higher affinity for the 5-HT1B receptor and is less selective for the 5-HT1D receptor compared to Rizatriptan.
**Option B:** **Almotriptan** - Almotriptan is another triptan, but it has a different pharmacokinetic profile and is less potent than Rizatriptan.
**Option C:** **Ergotamine** - Ergotamine is an ergot alkaloid that acts as a 5-HT1B/1D receptor agonist but also has other mechanisms of action, including vasoconstriction and inhibition of prostaglandin synthesis. It is not as selective or potent as Rizatriptan.
**Clinical Pearl / High-Yield Fact**
Triptans, like Rizatriptan, are most effective when used early in the course of a migraine attack, within the first 4-6 hours of onset. They are not recommended for use in patients with a history of ischemic heart disease or uncontrolled hypertension.
**Correct Answer:** C. Rizatriptan