Metabolic transformation (Phase-I) is

RRB Staff Nurse Mumbai-2015

Pharmacology

Easy

Appeared in: RRB Staff Nurse Mumbai-2015

Explanation

Phase I metabolic reactions are functionalization reactions that introduce or unmask a polar functional group on a drug molecule.
The primary types of Phase I reactions are oxidation, reduction, and hydrolysis.
The main goal of Phase I is to convert a lipophilic (fat-soluble) drug into a more polar (water-soluble) metabolite, preparing it for further metabolism or excretion.
The Cytochrome P450 (CYP450) enzyme system, primarily located in the liver, is the most important catalyst for Phase I oxidative reactions.

Option A: Acetylation and methylation are types of conjugation reactions, which are characteristic of Phase II metabolism, not Phase I.
Option C: Glucuronide formation (glucuronidation) is the most common type of Phase II conjugation reaction, where glucuronic acid is attached to the drug to make it highly water-soluble for excretion.
Option D: Binding to plasma proteins is a key step in drug distribution, which determines how a drug travels through the bloodstream. It is not a metabolic or biotransformation process.

Visual 1: Flowchart: Illustrating the two-step process of drug metabolism. Step 1 (Phase I) shows a lipophilic drug undergoing oxidation to add an -OH group. Step 2 (Phase II) shows the metabolite being conjugated with glucuronic acid, resulting in a large, water-soluble compound ready for renal excretion.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Phase I Drug Metabolism as background academic context rather than a clinical decision trigger.
The liver is the primary site of drug metabolism. Nurses must monitor liver function tests (e.g., ALT, AST) in patients on long-term medications, as impaired liver function can lead to drug toxicity due to reduced metabolism.
Certain foods and drugs can induce or inhibit CYP450 enzymes. For example, grapefruit juice inhibits CYP3A4, increasing levels of drugs like statins. Nurses should educate patients about these critical interactions.
The 'first-pass effect' occurs when a drug administered orally is extensively metabolized by the liver during its first pass through the portal circulation, reducing its bioavailability. This is why some drugs cannot be given orally.

How to Approach the Question

Identify the core concept in the question stem, which is 'Phase-I' 'Metabolic transformation'.
Recall the two major phases of drug metabolism: Phase I (functionalization) and Phase II (conjugation).
Characterize the reactions in each phase. Phase I involves oxidation, reduction, and hydrolysis. Phase II involves adding a molecule, such as glucuronide, acetate, or a methyl group.
Evaluate each option against this framework.
Option A (Acetylation/methylation) and C (Glucuronide formation) are clearly Phase II reactions.
Option D (Protein binding) is part of pharmacokinetics but relates to distribution, not metabolism.

Concept Tested & Keywords

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