Unit 1: General Pharmacology (Pharmacokinetics)

Semester 4

BP404T

Introduction to General Pharmacology (Pharmacokinetics)

Pharmacology is the core biological science of drug action. This first unit introduces fundamental concepts, defining what a drug is, and mapping the various routes by which a drug enters the body (Enteral vs Parenteral). The bulk of the unit focuses on Pharmacokinetics—the mathematical timeline of a drug’s life within the patient. You will explore how drugs are Absorbed across gut membranes, Distributed into fat and muscle, Metabolized by liver enzymes, and Excreted by the kidneys (ADME).

Syllabus & Topics

1Introduction to Pharmacology: Definitions and Scope.
2Nature and sources of drugs. Essential drugs concept and orphan drugs.
3Routes of drug administration: Enteral, Parenteral, Topical.
4Pharmacokinetics: Membrane transport (Passive diffusion, Active transport).
5Absorption of drugs and factors modifying absorption.
6Distribution: Volume of Distribution (Vd), Plasma protein binding, Tissue binding.
7Metabolism (Biotransformation) and First-Pass effect.
8Excretion: Renal and non-renal clearance.

Learning Objectives

Compare the advantages and disadvantages of different routes of drug administration.

Understand the principles of drug transport across biological lipid membranes.

Analyze the factors influencing the Volume of Distribution and half-life.

Explain the significance of the First-Pass effect in oral drug dosing.

Frequently Asked Questions (FAQs)

Q1. What is the Difference Between Pharmacokinetics and Pharmacodynamics?

Pharmacokinetics refers to “what the body does to the drug” and includes the processes of Absorption, Distribution, Metabolism, and Excretion (ADME). Pharmacodynamics refers to “what the drug does to the body,” including its mechanism of action, receptor interactions, and resulting physiological or therapeutic effects.

Q2. Why Are Some Drugs Given Sublingually or Rectally Instead of Orally?

Orally administered drugs pass through the portal circulation to the liver before reaching systemic circulation, where they may undergo significant first-pass metabolism. Sublingual and lower rectal routes bypass the liver initially, allowing the drug to enter systemic circulation directly. This makes such routes useful for drugs like Nitroglycerin, which would otherwise be extensively metabolized in the liver.

Q3. How Does Ionization Affect Drug Absorption?

Biological membranes are lipid-rich, and only the un-ionized (lipid-soluble) form of a drug can readily cross them by passive diffusion. Weak acidic drugs such as Aspirin remain largely un-ionized in the acidic environment of the stomach and are better absorbed there. Weak basic drugs are more un-ionized in the alkaline intestine and are preferentially absorbed in that region.

Q4. What is the Volume of Distribution (Vd)?

Volume of distribution (Vd) is a theoretical volume that relates the amount of drug in the body to the concentration of drug in the plasma. A high Vd, such as with Chloroquine (approximately 13,000 L), indicates extensive distribution into tissues with low plasma concentration, whereas a low Vd suggests the drug remains largely confined to the plasma.