Introduction to General Pharmacology: Foundations, Drug Sources, and Pharmacokinetics

Overview

The first unit of the NPTL General Pharmacology course introduces fundamental concepts of drugs, their actions, routes of administration, interactions, and adverse reactions. By the end of the session students should have a solid grounding in the essential principles of pharmacology.

What Is Pharmacology?

• Derived from Greek pharmakon (drug) + logos (science).
• Studies the actions of drugs on living systems, including:
• Physical & chemical properties
• Biochemical & physiological effects
• Mechanisms of action
• Therapeutic uses
• Adverse effects

Branches of Pharmacology

1. Medical Pharmacology – use of drugs for diagnosis, prevention, suppression, and treatment of disease.
2. Clinical Pharmacology – scientific study of drug kinetics and dynamics in patients and healthy individuals to determine safe and effective dosing.
3. Experimental Pharmacology – screening and discovery of new drug candidates.
4. Systemic Pharmacology – drug effects on specific organ systems (nervous, cardiovascular, respiratory, endocrine, etc.).

Scope & Importance

• Connects chemistry, physiology, biochemistry, and clinical medicine.
• Guides rational drug use, supports drug discovery, and underpins personalized medicine and pharmacogenomics.

Definitions

• Drug: Any chemical substance used for diagnosis, prevention, or treatment of disease.
• Medicine: A formulated, approved drug prepared in safe dosage forms (tablet, capsule, injection, syrup, etc.).

Sources of Drugs

• Natural origin – plants (e.g., morphine, atropine), animals (insulin, thyroxine), minerals (lithium, iron), microbes (penicillin, streptomycin).
• Semi‑synthetic – natural scaffold modified chemically (e.g., heroin from morphine, ailine from penicillin).
• Synthetic – fully laboratory‑made compounds (e.g., sulfonamides, barbiturates, paracetamol).
• Biotechnological – recombinant DNA products (insulin, growth hormone, monoclonal antibodies).

Pharmacokinetics vs. Pharmacodynamics

• Pharmacokinetics (PK) – what the body does to the drug: Absorption → Distribution → Metabolism → Excretion (ADME).
• Pharmacodynamics (PD) – what the drug does to the body: interaction with receptors, therapeutic effects, side‑effects.

Absorption

• Entry of drug from administration site into systemic circulation.
• Routes: oral, subcutaneous, intramuscular, intravenous, etc.
• Rate and extent of absorption determine dose and dosing frequency.

Distribution

• Transport of drug from bloodstream to tissues.
• Selective distribution examples:
• Epinephrine → iris
• Tetracyclines → bone & teeth (calcium affinity)
• Heavy metals → hair & nails
• Dioxin → heart tissue
• Thyroxine → adipose tissue

Transport Mechanisms (Bio‑transportation)

1. Passive diffusion (including filtration)
2. Facilitated diffusion (carrier proteins)
3. Active transport (energy‑dependent)
4. Special transport (e.g., ion channels) Detailed mechanisms will be covered in later sessions.

Metabolism (Bio‑transformation)

• Primarily occurs in the liver via enzymes such as cytochrome P450.
• Phase I – functional group modification (oxidation, reduction, hydrolysis).
• Phase II – conjugation to increase polarity for excretion.
• Importance:
• Terminates drug action after therapeutic effect.
• Prevents accumulation and toxicity.
• Examples:
• Morphine → inactive glucuronide.
• Levodopa → active dopamine (pro‑drug).
• Heroin → morphine (active metabolite).
• Parathion → toxic paraoxon.

Excretion

• Removal of unchanged drug or metabolites from the body.
• Major routes:
• Renal – urine (e.g., furosemide, ethacrynic acid)
• Biliary – feces (e.g., tetracycline, chlorophenol)
• Pulmonary – exhaled air (e.g., inhalational anesthetics, alcohol)
• Other – sweat, saliva, breast milk (e.g., vitamin C, caffeine, morphine).
• Clinical relevance: drugs excreted in breast milk may affect newborns; dosing adjustments may be needed in renal or hepatic impairment.

Clinical Implications

• Understanding ADME is essential for:
• Determining onset, intensity, and duration of drug action.
• Designing appropriate dosing regimens.
• Anticipating drug interactions and adverse reactions.
• Making safe prescribing decisions during pregnancy or lactation.

Looking Ahead

The next session will delve deeper into pharmacokinetic and pharmacodynamic concepts, exploring drug‑interaction mechanisms, dose‑response relationships, and therapeutic monitoring.

A solid grasp of pharmacology’s basic principles—drug definitions, sources, and the ADME processes—provides the foundation for safe, effective, and rational use of medicines in clinical practice.