March 27, 2005[每周一问]No.2 最常用的镇痛药物—阿片样物质
Today we begin a discussion of the most commonly used analgesics in the management of pain, opioids.
1. What is the difference between the terms opiate and opioid?
2. Define the terms agonist, partial agonist, mixed agonist/antagonist, and antagonist.
3. Which are the synthetic and semisynthetic opioids? What is the difference?
今天我们开始讨论在疼痛治疗中最常用的镇痛药物—阿片样物质
1． 常用术语鸦片剂（或阿片类药opiate）与阿片样物质（opioid）的区别？
2． 阿片受体激动剂、部分激动剂、激动/拮抗剂、拮抗剂的定义？
3． 合成与半合成阿片类药物有哪些？不同之处？
[每周一问]No.2 最常用的镇痛药物—阿片样物质
常用术语鸦片剂（opiate）与阿片样物质（opioid）的区别？
鸦片剂（opiate）指来自于鸦片（罂粟植物的汁）的所有药物。至少有一打以上不同的生物碱类鸦片，可以分类为菲剂或苄基异喹啉剂。主要的菲剂是吗啡、可待因、二甲氢吗啡；主要的苄基异喹啉剂是盐酸罂粟碱与那可丁（呼吸系统药物/镇咳药）；这些可以称为鸦片制剂，虽然盐酸罂粟碱与那可丁没有类吗啡样的镇痛特性。
阿片样物质（opioid）指的包括天然的与合成的所有药物，作用于机体的特殊受体，至少产生一些类吗啡样作用；或者作用于那些产生拮抗吗啡作用的受体。这些特殊受体称为阿片受体，包括mu（μ）, delta（δ）,和kappa（κ）三种亚型（中国还分有σ亚型，但是其是否为阿片受体尚无定论，因为没有找到其内源性配基）。阿片药物分为激动剂、部分激动剂、激动—拮抗剂和拮抗剂。
阿片激动剂、部分激动剂、激动/拮抗剂、拮抗剂的定义？
激动剂：作用于受体并刺激受体产生吗啡样作用的物质
部分激动剂：作用于受体并刺激受体产生低于吗啡作用的物质
激动拮抗剂：作用于阿片类受体一亚型产生拮抗作用，同时可作用于另一亚型产生部分激动作用的物质
拮抗剂：作用于阿片类受体，并不激动该受体，反而阻止其他阿片类药物与受体结合的物质。
合成与半合成阿片类药物有哪些？不同之处？
半合成阿片药物包括那些需要对吗啡的结构进行相对简单化学处理后获得的药物，包括可待因和海洛因。
合成的阿片药物是在体外人工合成，而不是对吗啡结构进行化学处理。
吗啡可以通过实验室合成获得，但是合成不是主要获得途径。是因为可以容易的从罂粟树提纯出吗啡，而且费用很低。 
What is the difference between the terms opiate and opioid?
The term opiate refers to all drugs derived from opium—the juice of the poppy plant. There are more than a dozen distinct alkaloids of opium, and these can be categorized as either phenanthrenes or benzylisoquinolines. The major phenanthrenes are morphine, codeine, and thebaine, and the principal benzylisoquinolines are papaverine and noscapine; all of these could be appropriately called opiates, although papaverine and noscapine do not have morphine-like analgesic properties.
The term opioid refers to all drugs, naturally existing and synthesized, that bind to a group of specific receptors in the body and produces at least some morphine-like effects, or binds to these receptors and antagonizes morphine's effects. These specific receptors are now called opioid receptors and include mu, delta, and kappa subtypes. Opioids can be classified as agonists, partial agonists, agonist-antagonists, and antagonists:
Define the terms agonist, partial agonist, mixed agonist/antagonist, and antagonist.
Agonist binds to receptor and stimulates the receptor similarly to morphine
Partial Agonist binds to receptor and stimulates the receptor to a level below that which can be achieved by morphine
Mixed agonist/antagonist has antagonist effect on certain opioid receptor subtypes while acting as a (partial) agonist on another opioid receptor subtype.
Antagonist binds to opioid receptor, but does not stimulate receptor and prevents other opioids from binding to the receptor
Which are the synthetic and semisynthetic opioids? What is the difference?
The semisynthetic opioids include the agents that require relatively simple chemical modifications of morphine. These include codeine (methylmorphine) and heroin (diacetylmorphine).
The synthetic opioids are manufactured in vitro rather than by chemical modification of morphine.
Morphine can be created in a laboratory, but is largely not synthesized. This is because it is so easily and inexpensively derived and purified from the poppy plant. 
