Difference Between Phase I and Phase II Metabolism

Thekeydifference在第一阶段和第二阶段代谢之间是the phase I metabolism converts a parent drug to polar active代谢物II期代谢将母药转化为极性非活性代谢产物.

代谢（药物代谢）是anabolic and catabolicbreakdown of drugs by living organisms. Hence, drug metabolism is an important aspect of living systems. It occurs throughenzymatic reactions. Furthermore, drug metabolism is of three phases; Phase I (modification), Phase II (conjugation) and Phase III (further modification and excretion) and all three phases actively involve to detoxify and remove xenobiotics from the cells.

内容

1.Overview and Key Difference
2.What is Phase I Metabolism
3.What is Phase II Metabolism
4.相似性阶段我和阶段II Metabolism
5.Side by Side Comparison – Phase I vs Phase II Metabolism in Tabular Form
6.概括

什么是I期代谢？

Phase I reactions convert a parent drug to polar active metabolites through unmasking or insertion of a polar functional group. Therefore, in phase I drug metabolism, reactions occur through oxidation (cytochrome p450 monooxygenase system), reduction (NADPH cytochrome P450 reductase), hydrolysis (esterases), etc.

Here, a range of enzymes reacts to introduce polar reactive groups to the substrate (drug). Hence, it is the phase called modification. The most common modification is hydroxylation. It is catalyzed by cytochrome P-450 dependent mixed function oxidase system.

此外，在I期期间的常见氧化反应涉及将C-H键转化为C-OH键。而且，这很重要，因为它将前药（药理学无活性的药物）转换为活性药物。同样，I期代谢可以将无毒分子转化为有毒分子。但是，由I期代谢代谢代谢的药物具有更长的半衰期。

What is Phase II Metabolism?

II期反应通过将亚组的结合与-sh，-oH，-nh转化为极性代谢产物₂药物的功能组。因此，II期代谢是通过甲基化（甲基转移酶），乙酰化（N-乙酰基转移酶），硫酸化（硫代转移酶）和葡萄糖醛酸糖苷（UDP-葡萄糖苷糖基转移酶）。

The conjugated metabolites have increased molecular weight and become less active than the drug substrate. Therefore, these metabolic products are renally excreted. Individuals with deficient acetylation capacities suffer prolonged or toxic responses to normal drug doses due to low levels of metabolic rates.

I期和II期代谢之间有什么相似之处？

• I阶段I和II代谢都涉及药物合成代谢和分解代谢。
• Also, both phases produce polar molecules.
• And, they occur in living systems.

I期和II期代谢有什么区别？

Phase I and phase II metabolism are two of the three phases of drug metabolism. Phase I metabolism converts a parent drug to polar active metabolites while phase II metabolism converts parent into polar inactive metabolites. Therefore, this is the key difference between phase I and phase II metabolism. Furthermore, phase I metabolism occurs via unmasking or insertion of polar functional groups while phase II metabolism occurs via conjugation of subgroups. Hence, this is another difference between phase I and phase II metabolism.

Moreover, a further difference between phase I and phase II metabolism is that the reactions involving in phase I metabolism are oxidation, reduction and hydrolysis while the reactions involving in phase II metabolism are Methylation, glucuronidation, acetylation and sulfation.

The below infographic represents more details on the difference between phase I and phase II metabolism.

摘要 - I期与II期代谢

代谢（药物代谢）是anabolic and catabolic breakdown of drugs by living organisms. The key difference between phase I and phase II metabolism is that the phase I reactions convert a parent drug to polar active metabolites through unmasking or insertion of polar functional groups whilst phase II reactions convert a parent drug to polar inactive metabolites through conjugation of subgroups to -SH, -OH and -NH₂药物的功能组。此外，由I期代谢代谢的药物的半衰期比由II期代谢代谢的药物更长。

Reference:

1.“Phase I Drug Metabolism.” H2NC6H4CO2C2H5, Drugs.Available here

Image Courtesy:

1.”Xenobiotic metabolism”By TimVickers – Own work, (Public Domain) viaCommons Wikimedia
2. toxsulfotep的“亚硫酸代谢物” - 自己的工作，(CC BY-SA 3.0)viaCommons Wikimedia