Principles of Drug Action

Principles of Drug Action

General Introduction

Presented by Dr. George Ainooson from the Department of Pharmacology, Kwame Nkrumah University of Science and Technology (KNUST), Kumasi, Ghana.

Learning Outcomes

At the conclusion of this module, students will be able to:

  • Demonstrate comprehensive knowledge of modern pharmacology, encompassing the molecular basis of receptors and cell signaling to the systemic effects of drugs.
  • Identify major classes of drug receptors and the sites of drug action within the body. This includes understanding pharmacological mechanisms through which different classes of drugs can alter biochemical, physiological, or pathophysiological parameters to either achieve therapeutic effects or produce unwanted side effects.
  • Demonstrate understanding of dose-response curves, which are essential in determining drug potency, efficacy, and toxicity.

Terminologies

Pharmacology
  • The term originates from the Greek word "Pharmakon," meaning drug, medicine, or poison.
  • Another Greek term, "Logos" or "logia," translates to word, discourse, or the study of a subject (science of).
Definition of Pharmacology
  • Pharmacology can be defined as the study of how chemical agents affect the functions of living systems.
  • It involves examining sources, physical and chemical properties, biochemical and physiological actions, mechanisms of action, absorption, distribution, biotransformation, excretion, therapeutic effects, and other applications of drugs.

Major Divisions of Pharmacology

  • Pharmacodynamics: This branch examines what the drug does to the body, covering therapeutic and adverse effects, along with underlying mechanisms.
  • Pharmacokinetics: This branch explores what the body does to the drug; it includes the processes of Absorption, Distribution, Metabolism, and Excretion (ADME).

Source of Drugs

Natural Sources

Plant Origin:

  • Digoxin: Derived from the foxglove (Digitalis).
  • Morphine: Extracted from the opium poppy.
  • Quinine: Sourced from the cinchona tree.
  • Atropine: Obtained from Atropa belladonna (deadly nightshade).

Animal Origin:

  • Insulin: Hormone produced by the pancreas, used in diabetes treatment.
  • Vitamin B12: Essential for proper red blood cell formation and neurological function.
  • Thyroid Hormone: Involved in regulating metabolism and growth.

Microorganisms:

  • Penicillins: Derived from Penicillium species, used as antibiotics.
  • Streptomycin: Obtained from Streptomyces griseus, used to treat tuberculosis.

Mineral Origin:

  • Lithium: Used in the treatment of bipolar disorder.
  • Potassium permanganate: Utilized in various medicinal applications.
  • Sodium bicarbonate: Used as an antacid.
  • Aluminium hydroxide: Commonly found in antacids.
  • Fluoride: Typically used in dental applications.
Synthetic Sources

Two categories are identified:

  1. Semi-synthetic Sources:
    These are substances created by chemically modifying pure compounds derived from natural sources, often through biotechnological processes. For instance, many antibiotics such as cefuroxime, ceftriaxone, cloxacillin, and oxacillin fall under this category.

  2. Synthetic Drugs:
    These drugs are developed through modifications of existing compounds, focusing on either enhancing efficacy or altering side effects through structure-activity relationships, often employing receptor models as guides. Examples include ranitidine, propranolol, and Sildenafil (commonly known as Viagra).

Modification of Natural Compounds - Opioids

Example of modifications in the opioid class includes:

  • From poppy to morphine:
    • Natural opioid alkaloid transformations are significant.
    • Raw opium is processed to produce various forms of morphine, codeine, narcotine, and papaverine.
    • The transformations from opium tincture (laudanum) to synthetic opioids like methadone and heroin illustrate the pathway from natural source to modified compounds for therapeutic use.

Assignment

Students are tasked with researching the main clinical indications for the following substances:

  • Digoxin
  • Quinine
  • Morphine
  • Methadone
  • Lithium

Drug Nomenclature

Drugs can be referred to by several different names:

  • Chemical Name: This name is based on rules of chemical nomenclature. For example, acetylsalicylic acid is the chemical name for aspirin.
  • Proprietary Name: This is a brand or trade name legally owned by its manufacturer, often chosen for its market appeal. Examples include Malarex for chloroquine and Rocephin for ceftriaxone.
  • Generic Name: Also known as a non-proprietary or common name, this is assigned by a committee and refers to the drug as a recognized compound, such as Paracetamol (para-acetaminophen).

Functions of Medicines (Use of Drugs)

Medicines serve multiple functions in the healthcare system, including:

  1. Prevention: Some medicines are used prophylactically to prevent illness. Example: Vaccines for smallpox and polio, and fluoride to prevent dental caries.
  2. Cure: Certain drugs lead to the complete eradication of diseases, exemplified by antibiotics and anthelmintics.
  3. Treatment: Drugs that alleviate symptoms, particularly for chronic conditions, such as anti-asthmatics and anti-anginals, fall into this category.
  4. Suppression: These drugs suppress the symptoms and prevent disease progression, such as anticancer and antiviral medications.
  5. Diagnosis: Some substances aid in establishing a diagnosis or understanding a patient's condition, such as radiocontrast dye used in imaging procedures.
  6. Enhancement of Health: Certain compounds, like vitamins and minerals, are used to promote overall health and well-being.

References and Further Reading

  • Rang & Dale's Pharmacology - 10th Edition (2024)
  • Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th Edition (2022)
  • Medical Pharmacology at a Glance, Michael J. Neal - 9th Edition (2020)