药物代谢是药物的化学转化
转化为可被人体排出体外的水溶性化合物
药物代谢主要在肝脏进行，
而排泄主要发生在肾脏
给药后，药物必须穿过紧密堆积的细胞，
穿过细胞膜到达其作用位点
通常药物是亲脂性或脂溶性化合物，
细胞膜由磷脂组成，
所以药物能够穿过它们
然而，为了通过肾脏排泄，
有必要将药物转化为水溶性或亲水性化合物
药物通常通过口服或肠胃外给药
肠外药物绕过消化道
家长路线包括
注射，
透皮贴剂，
乳液，
吸入剂，
和栓剂
如果注射，药物会迅速进入全身循环并立即起效
如果口服，药物必须通过胃肠道细胞
药物穿过胃肠道细胞并通过肝门静脉到达肝脏
在药物进入全身循环之前，肝脏有机会代谢一些药物，
这称为首轮效应
在肝脏中，药物进入肝细胞
光滑内质网中的一系列酶将它们代谢
药物通过内质网磷脂膜移动
肝微粒体酶（例如
p450）将药物从亲脂性化合物转化为亲水性化合物
重复使用某些药物会增加代谢酶的数量并增加药物代谢
这称为酶诱导
相反，某些药物竞争与代谢酶结合，从而降低药物代谢
这称为酶抑制
一旦代谢，这些亲水性代谢物就会让细胞准备好被肾脏排泄
药物作用的持续时间和强度很大程度上取决于代谢率
代谢率的增加将通过促进排泄来减少药物的持续时间和强度
代谢率降低会增加药物持续时间和强度
影响代谢率的一些因素是首过效应，
肝脏疾病，例如肝硬化，
新生儿、老年人肝功能下降，
肝脏血流受损会降低代谢率，
肝酶的数量和类型的变化，
不良的饮食和营养会影响正常的肝功能，
由于剂量或患者体重而导致循环药物水平较高，需要更长的时间才能代谢

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Drug metabolism is the chemical conversion of drugs
药物代谢是药物的化学转化
into water soluble compounds that can be excreted by the body
转化为可被人体排出体外的水溶性化合物
Drug metabolism mainly takes place in the liver
药物代谢主要在肝脏进行,
while excretion mainly takes place in the kidneys
而排泄主要发生在肾脏
Following drug administration drugs must pass through tightly packed cells
给药后,药物必须穿过紧密堆积的细胞,
crossing cell membranes to reach their sites of action
穿过细胞膜到达其作用位点
Usually drugs are lipophilic or fat soluble compounds
通常药物是亲脂性或脂溶性化合物,
and cell membranes are composed of phospholipids
细胞膜由磷脂组成,
so drugs are able to cross them
所以药物能够穿过它们
However for excretion by the kidneys
然而,为了通过肾脏排泄,
it's necessary to convert drugs to water soluble or hydrophilic compounds
有必要将药物转化为水溶性或亲水性化合物
Drugs are usually administered orally or parenterally
药物通常通过口服或肠胃外给药
Parenteral drugs bypass the digestive tract
肠外药物绕过消化道
Parental routes include
家长路线包括
injection
注射,
transdermal patches
透皮贴剂,
lotions
乳液,
inhalants
吸入剂,
and suppositories
和栓剂
If injected the drugs reach general circulation quickly and have an immediate effect
如果注射,药物会迅速进入全身循环并立即起效
If taken orally drugs must pass through the cells of the gastrointestinal tract
如果口服,药物必须通过胃肠道细胞
Drugs cross through cells of the GI tract and travel to the liver via the hepatic portal vein
药物穿过胃肠道细胞并通过肝门静脉到达肝脏
The liver has a chance to metabolize some of the drug before it goes into general circulation
在药物进入全身循环之前,肝脏有机会代谢一些药物,
this is called the first pass effect
这称为首轮效应
In the liver drugs enter hepatic cells
在肝脏中,药物进入肝细胞
where a series of enzymes in smooth endoplasmic reticulum metabolize them
光滑内质网中的一系列酶将它们代谢
Drugs move through the phospholipid membrane of endoplasmic reticulum
药物通过内质网磷脂膜移动
Hepatic microsomal enzymes such as p450 convert drugs from lipophilic to hydrophilic compounds
肝微粒体酶(例如
Repeated use of certain drugs increases the amount of metabolic enzymes and increases drug metabolism
重复使用某些药物会增加代谢酶的数量并增加药物代谢
This is called enzyme induction
这称为酶诱导
Conversely certain drugs compete to bind to metabolic enzymes thereby decreasing drug metabolism
相反,某些药物竞争与代谢酶结合,从而降低药物代谢
This is called enzyme inhibition
这称为酶抑制
Once metabolized these hydrophilic metabolites leave the cell ready for excretion by the kidney
一旦代谢,这些亲水性代谢物就会让细胞准备好被肾脏排泄
A drug's duration and intensity of effect are largely determined by metabolic rate
药物作用的持续时间和强度很大程度上取决于代谢率
Increased metabolic rate will decrease drug duration and intensity by facilitating excretion
代谢率的增加将通过促进排泄来减少药物的持续时间和强度
Decreased metabolic rate increases drug duration and intensity
代谢率降低会增加药物持续时间和强度
A few of the factors affecting metabolic rate are the first pass effect
影响代谢率的一些因素是首过效应,
liver disease such as cirrhosis
肝脏疾病,例如肝硬化,
neonates in the elderly have decreased liver function
新生儿、老年人肝功能下降,
compromised blood flow to the liver will lower metabolic rate
肝脏血流受损会降低代谢率,
variation in amount and type of hepatic enzymes
肝酶的数量和类型的变化,
poor diet and nutrition can affect normal liver function
不良的饮食和营养会影响正常的肝功能,
and higher circulating drug levels due to dosage or patient's weight take longer to metabolize
由于剂量或患者体重而导致循环药物水平较高,需要更长的时间才能代谢