Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0600097 (Sedation)
 1,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Clonidine (Catapres, Catapresan), guanfacine (Estulic), and methyldopa (Aldomet) are the prototypes of centrally acting antihypertensive drugs. Clonidine and guanfacine are lipophilic drugs that readily penetrate into the brain, where they stimulate alpha-adrenergic receptors in the pontomedullary region. The stimulation of these central alpha-adrenergic receptors has been shown to activate an inhibiting neuron, which causes a reduction of peripheral sympathetic tone and a subsequent fall in arterial blood pressure and heart rate. Both a centrally initiated reduction of vagus reflex activity and the activation of presynaptic alpha 2-adrenergic blocking agents in the heart may contribute to the bradycardia. Studies indicate that methyldopa also penetrates into the brain, where it is converted into alpha-methylnorepinephrine. This amine may stimulate the same central alpha-adrenergic receptors as those activated by clonidine, which will result in a hypotensive effect. Possibly, alpha-methyldopamine might also play a role. Accordingly, the modes of action of clonidine and alpha-methyldopa probably are very similar at a basic level. The central adrenergic receptors probably are located postsynaptically. Their receptor demand corresponds more closely to that of the alpha 2-subtype. Central alpha 1-adrenergic receptors might possibly play a part in the modulation of vagally induced baroreflex bradycardia. A discussion on the pharmacological basis of the side effects of the centrally acting antihypertensives has been limited to those adverse reactions that are somehow related to alpha-adrenergic receptors. Sedation, a common side effect, appears to be mediated by central alpha 2-adrenergic receptors, at least in animal models.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The hypotensive activity and side effects of methyldopa, clonidine, and guanfacine. 609 46

Clonidine hydrochloride (Catapres), a potent antihypertensive agent, has been in clinical use since 1974 in the United States. Clonidine, an alpha-adrenergic receptor agonist, stimulates central alpha receptors in the depressor site of the vasomotor center of the medulla oblongata and hypothalamus, which diminishes efferent sympathetic tone to the heart, kidneys, and peripheral vasculature with a concomitant increase in vagal activity. Hemodynamic and renal effects include reduction in supine and erect blood pressure, heart rate, total peripheral resistance, plasma renin activity, and urinary aldosterone and catecholamine excretion, with little effect on resting cardiac output, response to exercise, and preservation of renal function. Clonidine alone produces a significant reduction in mean arterial pressure in all degrees of hypertension during acute and chronic administration, with little or no tendency toward tolerance or postural hypotension. Its antihypertensive potency is enhanced with the concomitant use of a diuretic or vasodilator, and it may be used in place of a beta blocker with equal efficacy in the diuretic plus vasodilator combination. Serious adverse effects are uncommon, with more than 93% of patients tolerating the drug well. Sedation and dry mouth, the most common adverse effects, are usually related to dose and duration and are minimized by gradually increasing the dose and by taking the major portion of the twice-daily schedule at bedtime. Clonidine may be safely given to patients with congestive heart failure, ischemic heart disease, obstructive lung disease, chronic renal insufficiency, and diabetes mellitus. Clonidine is one of the most versatile and effective agents presently available for the treatment of hypertension.
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PMID:Clonidine hydrochloride. 704 65