How Drugs Are Metabolized: Phases, Enzymes, Interactions & Clinical Impact

Drug Metabolism Explained: Phases, CYP450 System & Clinical Importance (For Healthcare Professionals)

Suggested Focus Keywords:

Drug metabolism

CYP450 enzymes

Phase I and Phase II reactions

CYP3A4 inhibitors and inducers

drug interactions

Hepatic metabolism

Learn how drug metabolism works, including Phase I & II reactions, CYP450 enzymes, inhibitors, inducers, and clinical implications in patient care.

How Drugs Are Metabolized: Phases, Enzymes, Interactions & Clinical Impact

Introduction to Drug Metabolism

Definition

Why drug metabolism is essential

Role in safety and efficacy

First-pass metabolism concept

Clinical hook: Why some drugs fail in diabetic & cardiac patients.

Sites of Drug Metabolism

Liver (Primary organ)

Intestine

Kidney

Lungs

Add small diagram suggestion (liver-centric metabolism flow).

Phase I Reactions (Functionalization Reactions)

Oxidation

Reduction

Hydrolysis

Role of CYP450 enzymes

Important CYP Enzymes:

CYP3A4

CYP2D6

CYP2C9

CYP2C19

Clinical example:

Sildenafil + CYP3A4 inhibitors → toxicity risk.

Phase II Reactions (Conjugation Reactions)

Glucuronidation

Sulfation

Acetylation

Methylation

Explain:

Phase II = more water-soluble → easy excretion.

Clinical example:

Paracetamol metabolism pathway.

CYP450 Enzyme System Explained

What is Cytochrome P450?

Where it is located

Why it causes drug interactions

CYP3A4 Inhibitors vs Inducers Table

Type

Effect

Example

Inhibitor

Drug level ↑

Ketoconazole

Inducer

Drug level ↓

Rifampicin

Factors Affecting Drug Metabolism

Age

Liver disease

Genetics (Poor vs Ultra-rapid metabolizers)

Drug interactions

Food (Grapefruit juice)

Clinical note for elderly diabetic patients.

Clinical Importance in Patient Care

Avoiding toxicity

Dose adjustment

Therapeutic drug monitoring

Special populations

Drug–Drug Interaction Case Study

Example scenario:

Patient on statin + clarithromycin

What happens?

Mechanism explanation

Management approach

Summary of key concepts

Importance for pharmacists & clinicians

Rational prescribing message

About the Author

Naeem Mustafa, Pharmacist

15+ years experience in pharmaceutical marketing & patient education.

Founder of PharmaServePK – Promoting Rational Drug Use & Health Awareness.