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Sites of biotransformation


Q. Mention the sites of bio transformation.
Ans:
(i) Liver (Principal site) most drugs
(ii) Kidney Morphine, Insulin (40%)
(iii) Lungs Prostanoids
(iv) Intestine Penicillin, Catecholamines.
(v) Blood Suxamethonium
(vi) Skin
Q: What are the Phases of bio transformation?

Ans: There are two Phases of biotransformation. These are-
(i) Phase-I (non-synthetic Phase). ,
(ii) Phase-II (Synthetic Phase).
Phase-I reaction: This reaction usually converts the parent drug to a more polar metabolites by introducing or removing a functional group e.g. (-OH, -NH2, -5H, -COOH).
Drug +/- functional group more polar metabolites.
Phase-II reaction: Phase-I metabolites conjugates with endogenous substance (glucouronic acid, acetic acid, methyl group, amino acid) to yield a drug conjugate complexes which are polar and readily excretable through the kidney.
More polar metabolities + (Amino acid/glucouronic acid/acetic acid)
Drug conjugate complex
Excretion
Q: Explain presystemic metabolism of drugs with examples. How can it be avoided?

Ans:  Pre-systemic/1' pass metabolism: Metabolism of drug in the stomach, intestinal wall and liver or in the lung before being reached into the systemic circulation is called first pass metabolism.
Hepatic first pass metabolism: Metabolism of drug in the liver before being reached into the systemic circulation is called hepatic first pass metabolism.
Example:
Morphine, Isoprenaline Undergo extensive metabolism in the liver
Insulin, oxitocin Protiolysis in GIT
It can be avoided by changing the route of drug administration parenternal route is suitable to avoid this.

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