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効能
血管拡張薬, αアドレナリン受容体拮抗薬
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説明
Phentolamine is also a derivative of imidazoline that exhibits a direct α-adrenoblocking,
muscle-relaxant effect on smooth muscle as well as cholinomimetic, histamine, and sympathomimetic effects. The chemical variation of its structure permits a few of its properties to
be more expressed. For example, the aforementioned tolazoline, 2-benzyl-2-imidazoline, a
structural analog of phentolamine, has more of an expressed muscle-relaxant effect on
smooth muscle than an α-adrenoblocking effect.
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使用
Anti-adrenergic.
Phentolamine is used to prevent or control hypertensive episodes that occurin patients with pheochromocytoma. It also has been used incombination with papaverine to treat impotence.
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定義
ChEBI: A substituted aniline that is 3-aminophenol in which the hydrogens of the amino group are replaced by 4-methylphenyl and 4,5-dihydro-1H-imidazol-2-ylmethyl groups respectively. An alpha-adrenergic antagonist, it is used fo
the treatment of hypertension.
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適応症
Human erectile tissue has a population of membrane
receptors that are predominantly of the -adrenoceptor
subtype. Phentolamine (Vasomax) is a nonselective -
adrenoceptor blocking agent (see Chapter 11), and like
other such agents, it has been used to treat ED.
Nonselective adrenoceptor antagonists may provoke a
reflex that increases both sympathetic outflow and the
release of norepinephrine.
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一般的な説明
Phentolamine isthe more effectiveα -blocker.
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作用機序
Its mechanism of action is as an α-adrenergic antagonist of both α1- and α2-receptors, causing vasodilation and reduction in peripheral resistance. When administered by intracavernosal injection, it is thought to cause relaxation of the cavernous smooth muscles and vasodilation of the penile arteries. This results in increased arterial blood flow into the corpus cavernosa as well as swelling and elongation of the penis. Venous outflow also is reduced, possibly as a result of increased venous resistance. Phentolamine is slowly released into venous circulation with minimal, if any, systemic effects. Time to peak effect is within 10 minutes, and duration of action when used with papaverine is 1 to 6 hours.
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臨床応用
Phentolamine has been used orally and intracavernosally
in the treatment of ED. Following oral administration,
phentolamine has a plasma half-life of about 30
minutes and a duration of action of 2 to 4 hours. An intracavernosal
injection of phentolamine results in the
drug reaching maximum serum levels in about 20 to 30
minutes. It is rapidly metabolized.
Phentolamine has been used in combination with
papaverine, chlorpromazine, and vasoactive peptides in
the treatment of ED.
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副作用
Side effects of phentolamine are dose related. It
may cause orthostatic hypotension, reflex tachycardia,
cardiac arrhythmias, and rarely, myocardial infarction.
Phentolamine also may reduce sperm motility in vitro.
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安全性プロファイル
Poison by subcutaneous, intravenous, and intraperitoneal routes. Moderately toxic by ingestion. Experimental reproductive effects. When heated to decomposition it emits toxic fumes of NOx.
