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Sites of biotransformation

Q. Mention the sites of bio transformation.
(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
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.
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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