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Chapter: Modern Medical Toxicology: Neurotoxic Poisons: Drugs Used in Psychiatry

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Sumatriptan - Anti-Migraine Drugs

Sumatriptan resembles 5-hydroxytryptamine in structure and is usually given subcutaneously in the treatment of migraine and cluster headaches.

Sumatriptan

·              Sumatriptan resembles 5-hydroxytryptamine in structure and is usually given subcutaneously in the treatment of migraine and cluster headaches. It can also be administered orally. Other members of the group include almotriptan, avitriptan fumarate, eletriptan, frovatriptan, naratriptan hydrochloride, rizatriptan, and zolmitriptan.

Mode of Action

·              Sumatriptan is a highly selective agonist at 5-HT receptors of the 5-HT1D or 5-HT1-like subtype, but is almost devoid of activity at 5-HT2 and 5-HT3 receptors. The resultant vasocon-striction can relieve the severity of migraine which is due to vasodilation in the cerebral circulation.

Adverse Effects

·              Unpleasant taste (oral use), injection site reaction, tingling, warm sensation, vertigo, fatigue, chest tightness, rarely myocardial ischaemia and infarction, and even asthma and ventricular arrhythmias.

·              Acute myocardial infarction, ventricular arrhythmias, and coronary vasospasm have occurred with therapeutic doses of subcutaneous and oral sumatriptan. Cardiac arrest has been reported. Chest tightness or pressure with therapeutic doses occurred in 5% of patients after subcutaneous sumatriptan and 3% of patients after oral sumatriptan.

·              A temporal association between subcutaneous dosing with sumatriptan for migraine and subsequent episodes of intracranial bleeding has been reported in some patients.

 

Drug Interactions

·              Sumatriptan should not be combined with 5-HT reuptake inhibitor antidepressants, MAOIs, or lithium. Caution should also be exercised with ergotamine and catecholamines.

Clinical (Toxic) Features

·              A few cases of overdose have so far been reported with mani-festations such as dysphoria, burning sensation over face, and sedation. Increased blood pressure may occur following overdoses.

·              Sumatriptan should never be given intravenously because of the potential for coronary vasospasm.

Treatment

·      Symptomatic and supportive measures. ECG and blood pressure should be monitored for at least 12 hours. For mild/moderate asymptomatic hypertension, pharmacologic intervention is generally not necessary.

·      Sedative agents such as benzodiazepines may be helpful in treating hypertension and tachycardia in agitated patients, especially if a sympathomimetic agent is involved in the poisoning. Vasodilation therapy may be required­.

·      For hypertensive emergencies (severe hypertension with evidence of end organ injury (CNS, cardiac, renal), or emergent need to lower mean arterial pressure 20 to 25% within one hour), nitroprusside is preferred. Nitroglycerin and phentolamine are possible alternatives. In the event of anginal pain, nitrites must be given.

·      Lignocaine and amiodarone are generally first line agents for stable monomorphic ventricular tachycardia, particularly in patients with underlying impaired cardiac function. Sotalol is an alternative for stable monomor-phic ventricular tachycardia. Amiodarone and sotalol should be used with caution if a substance that prolongs the QT interval and/or causes torsades de pointes is involved in the overdose. Unstable rhythms require cardioversion.

·      In the event of serotonin syndrome being precipitated, the recommended measures for its treatment must be under-taken.

 

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