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右甲嗎喃（Dextromethorphan），又名右美沙芬，英文簡稱DM或DXM，是一種鎮咳藥物，它的氫溴酸鹽（Dextromethorphan hydrobromide）常用於藥品中。
化學
Dextromethorphan is a salt of the methyl ether dextrorotatory isomer of levorphanol, a narcotic analgesic. It is chemically named as 3-methoxy-17-methyl-9(alpha), 13(alpha), 14(alpha)-morphinan hydrobromide monohydrate. DXM occurs as white crystals, is sparingly soluble in water, and freely soluble in alcohol. The drug is dextrorotatory in water (at 20 degrees Celsius, Sodium D-line) with a specific rotation of +27.6 degrees.
Dextromethorphan is metabolized by various liver enzymes and subsequently undergoes O-demethylation, N-demethylation, and partial conjugation with glucuronic acid and sulfate ions. Hours after dextromethorphan therapy, (in humans) the metabolites (+)-3-hydroxy-N-methylmorphinan, (+)-3-morphinan, and traces of the unchanged drug are detectable in the urine.
醫學上的用途
美國食品及藥物管理局在1958年批准右甲嗎喃可不需醫生處方而作為鎮咳藥發售。當時最廣泛使用的咳藥可待因有被濫用的可能性，也可成癮，右甲嗎喃在這些方面比可待因有所改善。右甲嗎喃不易造成物質依賴（身體缺乏某物質即產生生理反應），鎮靜副作用亦較少。
藥物效應動力學
At therapeutic doses, the drug acts centrally to elevate the threshold for coughing, without inhibiting ciliary activity. 右甲嗎喃在腸胃被迅速吸收，在口服後15至60分鐘內可發揮藥效。口服後藥力可維持大約3至8小時。Because administration of DXM can be accompanied by histamine release, its use in atopic children is very limited.
The average dosage necessary for effective antitussive therapy is between 10mg and 30mg every four to six hours.
According to the WHO committee on Drug Dependence, dextromethorphan, when used recreationally (see non-medical use of dextromethorphan), doesn't produce physical addiction but can generate slight psychological dependence in some users.
臨床藥理學
Following oral administration, dextromethorphan is rapidly absorbed from the gastrointestinal tract, where it enters the bloodstream and crosses the blood-brain barrier. The first-pass through the hepatic portal vein results in some of the drug being metabolized into an active metabolite of dextromethorphan, dextrorphan, the 3-hydroxy derivative of dextromethorphan. The therapeutic activity of dextromethorphan is believed to be caused by both the drug and this metabolite. Dextromethorphan is predominantly metabolized by the liver, by various hepatic enzymes. Through various pathways, the drug undergoes (O-demethylation (which produces dextrorphan), N-demethylation, and partial conjugation with glucuronic acid and sulfate ions. The inactive metabolite (+)-3-hydroxy-N-methylmorphinan is formed as a product of DXM metabolism by these pathways. One well known metabolic catalyst involved is a specific cytochrome P450 enzyme known as 2D6, or CYP2D6. A significant portion of the population has a functional deficiency in this enzyme (and are known as poor CYP2D6 metabolizers). As CYP2D6 is the primary metabolic pathway in the inactivation of dextromethorphan, the duration of action and effects of dextromethorphan are significantly increased in such poor metabolizers. Deaths and hospitalizations have been reported in recreational use by poor CYP2D6 metabolizers.
A large number of medications (including antidepressants) are potent inhibitors of CYP2D6 (see CYP2D6 article). There exists, therefore, the potential of drug-drug interactions between dextromethorphan and concomitant medications. There have been reports of fatal consequences arising from such interactions.
Dextromethorphan crosses the blood-brain barrier, and the following pharmacological actions have been reported:
- NMDA glutamatergic receptor antagonist
- Dopamine reuptake inhibitor
- σ1 and σ2 receptor agonist (Zhou & Musacchio, 1991)
- α3β4 nicotinic receptor antagonist *
- Serotonin reuptake inhibitor *
歷史
Dextromethorphan was first patented with , and was approved for over-the-counter purchase as an antitussive in 1958.
非醫學的用途
For a history of and information on the use of dextromethorphan as a dissociative or hallucinogen, see non-medical use of dextromethorphan. 药物
Dextromethorphan | Dextromethorphan | Dextrometorfano | Dekstrometorfaani | Dextrométhorphane | Dextromethorphan | Dextromethorphan | Dekstrometorfan | DXM
"右甲嗎喃"