Pharmacology in Medical Sciences Study Notes

Introduction to Medical Sciences - Pharmacology (Dr. Benedict Brown)

Thanks to Sumrah Shaffiq for contributions to the content.

Objectives

  • Affinity, Potency, Efficacy: Understand definitions and importance in pharmacology.
  • Types of Agonists/Antagonists: Differentiate between agonists, partial agonists, inverse agonists, antagonists (both competitive and non-competitive) and their receptor interactions.
  • Dose-Response Curves: Ability to interpret curves identifying threshold, ED50, and drug ceiling.
  • Dose Calculations: Skill in performing simple calculations related to dosing.
  • Receptor Classes: Recognize drugs acting at major receptor classes with examples.
  • Drug Action at Synapse: Awareness of drug mechanisms at synapses with examples.

Pharmacodynamics and Pharmacokinetics

  • Pharmacodynamics:

    • Specific to drug or class.
    • Focus on interaction with cellular components.
    • Describes concentration-effect relationships and modification of disease progression.

  • Pharmacokinetics:

    • Non-specific processes.
    • Steps of absorption, time to onset of effect, and elimination from the body.

Properties of Drugs

Affinity
  • The strength of binding between a drug and its receptor; higher affinity means the drug binds more tightly.
Efficacy
  • Measure of the functional change induced by drug-receptor interaction; high efficacy means a significant change occurs upon binding.
Potency
  • Refers to the amount or dose of drug required to produce a biological effect; illustrated quantitatively as the drug concentration needed for effective response.

Receptors

  • Macromolecules that facilitate chemical signaling between cells.
  • Receptors change cell activity when stimulated and must recognize the specific signaling molecule.

Pharmacological Terminology

Agonists
  • Initiate a cellular response upon binding; characterized by high affinity and efficacy.
Partial Agonists
  • Also bind receptors but produce a lower maximum response compared to full agonists.
Inverse Agonists
  • Bind to receptors to produce an opposite effect than that of agonists.
Antagonists
  • Bind to receptors but do not elicit a response; they possess affinity but lack efficacy.
Types of Antagonists
  • Competitive Antagonists: Bind the same site as agonists, blocking their effect.
  • Non-competitive Antagonists: Bind an allosteric site, preventing receptor activation regardless of agonist presence.

Dose-Response Concepts

  • Ceiling: Lowest dose yielding maximal effect.
  • ED50: Dose for 50% of maximum response.
  • Threshold: Smallest dose that produces noticeable effects.

Drug Action Mechanisms

  • General Mechanisms:
    • Action on receptors, synapses, enzymes, and cell transport.
  • Receptor Families:
    • Different types include ligand-gated ion channels, G-protein coupled receptors, receptor kinases, and nuclear receptors.
1. Ligand-Gated Ion Channels
  • Transmembrane channels opened by ligand binding (e.g. neurotransmitters like glutamate, serotonin).
2. G-Protein-Coupled Receptors (GPCRs)
  • Linked to G proteins; initiate cellular response through cascade reactions following ligand binding.
3. Receptor Kinases
  • Activate intracellular signaling cascades; mainly activated by growth factors.
4. Nuclear Receptors
  • Intracellular, activation requires lipid-soluble ligands (e.g., steroid hormones).

Neurotransmitters and Synapses

  • Neurotransmitters are critical for nerve impulse transmission across synapses.
  • Presynaptic Neurons: Release neurotransmitters.
  • Postsynaptic Neurons: Receive neurotransmitters.
Common Neurotransmitters
  • Acetylcholine: Muscle action, learning, memory. Low levels linked to Alzheimer’s.
  • Noradrenaline: Mood and alertness control. Low levels lead to depression.
  • Dopamine: Movement and emotion regulation; involved in disorders like Parkinson’s and schizophrenia.
  • GABA: Major inhibitory neurotransmitter; low levels relate to anxiety.
  • Serotonin: Regulates mood and arousal; deficits linked to depression.
Drug Effects on Neurotransmission
  • SSRIs: Selective serotonin reuptake inhibitors that increase serotonin availability.
  • TCAs: Block both serotonin and noradrenaline reuptake; enhance mood.

Enzymatic Actions

  • Enzymes are proteins that catalyze specific reactions (lock & key model).

Drugs Affecting Enzymatic Activity

  • Inhibitors, such as non-selective NSAIDs (Aspirin), target specific inflammation-related enzymes.

Cell Transport Mechanisms

Calcium Channel Blockers
  • Drugs like amlodipine relax smooth muscle via calcium channel blockade, reducing heart rate.
Local Anaesthetics
  • Block sodium channels for temporary loss of sensation; potential adverse effects on the heart/CNS.

Summary

  • An understanding of pharmacodynamics, receptor interactions, neurotransmitter functions, and enzyme systems is essential in pharmacology.
  • Mastering these principles enhances the approach to safe and effective drug use in medical practices.