Psychopharmacology – Lecture 1.1
Definition and Classification:
What is Pharmacology ?
Pharmacology is the scientific study of how drugs and other chemical substances interact
with living organisms, focusing on their effects, mechanisms of action, and the physiological
responses they provoke.
This field encompasses two main areas: pharmacokinetics (how the body processes the
drug) and pharmacodynamics (how the drug affects the body).
What is a Pharmacon ?
A Pharmacon refers to any substance, typically a medicine or pharmaceutical product, that is
used for therapeutic purposes.
It can be a natural or synthetic compound designed to treat, prevent, or diagnose
diseases.
The term pharmacon is often used to describe the substance before it is formally
processed and prescribed as a drug.
Definition of “Drug”:
English Definition: A drug is any pharmacologically active substance that causes a physiological
effect in the body.
This can include medications used for treatment, as well as substances with psychoactive
properties, such as narcotics or stimulants, that may be used for recreational purposes or
abuse.
Dutch Definition: A drug is a psychoactive substance, typically used for abuse, that has a
drugging effect on the body, potentially leading to dependence or addiction.
This category includes substances that act as stimulants or narcotics.
Classification methods:
Chemical Structure: Although this can be interesting, the same chemical structure might lead to
different effects in the body.
Working Mechanism: This is the ideal way to classify, but often the exact mechanism is not fully
understood.
, Behavioral Effects: This method is the easiest and is directly related to the disorder being
treated.
Two Main Classification Systems:
Overview:
Established in 1976, ATC is the most widely used system for classifying drugs.
Endorsed as the WHO gold standard for drug nomenclature.
Drugs are categorized based on their therapeutic indications and anatomical site of action.
Classification Approach:
Drugs are grouped into 14 main categories based on anatomical and therapeutic
considerations (e.g., nervous system, cardiovascular system).
Further subcategorized by therapeutic use, pharmacological properties, and chemical
characteristics.
Examples: Antipsychotics/Antidepressants.
Cons Stigmatizing for patients: Labels like "antipsychotics" or "antidepressants" can
carry negative connotations.
Inflexible for off-label uses: Drugs used for non-primary indications (e.g.,
antidepressants for pain management) may not fit neatly into categories.
Additionally, the focus on indications rather than mechanisms can overlook
important pharmacological nuances
The ATC classification of psychotropic [drugs, which affect the mind, emotions, and behavior] drugs
includes five main classes:
Antipsychotics: Used primarily to treat symptoms of psychosis, such as in schizophrenia or
bipolar disorder. They help manage symptoms like delusions, hallucinations, and agitation.
Antidepressants: These drugs are used to treat depression and may also help with anxiety,
chronic pain, and other conditions. They work by altering the levels of neurotransmitters in the
brain, such as serotonin and norepinephrine.
Anxiolytics (Anti-anxiety medication): Used to treat anxiety disorders. They help reduce
symptoms like excessive worry, panic attacks, and tension. Common classes include
benzodiazepines and certain antidepressants.
Mood Stabilizers: Primarily used in the treatment of bipolar disorder, these drugs help to
stabilize mood swings between mania and depression.
Hypnotics: Also known as sleeping pills, these are used to treat insomnia or other sleep-related
disorders. They help induce and maintain sleep.
Other Relevant Drug Classes:
Anti-Epileptics: Medications used to treat seizures and epilepsy.
, Stimulants: Drugs that increase alertness and activity levels.
Narcotic Painkillers: Opioid-based drugs used to manage severe pain.
Central Nervous System (CNS) Suppressors: Drugs that reduce overall CNS activity.
Psychedelics & Hallucinogens: Drugs that alter perception, mood, and cognitive processes.
Natural Sources → Mescaline: Derived from the peyote cactus and San Pedro cactus.
Often compared to or grouped with LSD due to similar hallucinogenic effects
Overview:
Introduced in 2018, NbN represents a pharmacology-driven approach to drug classification.
Developed by a task force of five major neuroscience organizations to address the limitations
of indication-based systems like ATC.
Focuses on mechanisms of action rather than disorders treated.
Classification Approach:
Drugs are categorized based on their primary mechanisms of action at the molecular and
receptor levels (e.g., serotonin reuptake inhibition, dopamine antagonism).
Avoids using disorder-specific terms, instead focusing on what the drug does
pharmacologically.
Example: Serotonin/dopamine antagonists with antipsychotic action.
Cons May be more complex and less intuitive for general clinical practice.
Newer system: Has not yet been widely adopted or fully integrated into global
health frameworks like WHO standards.
Limited evidence base: Requires more clinical data to validate its classifications.
Administration
[1] Absorption: from site of administration → blood.
This is the process where the drug moves from the site of administration into the bloodstream.
Different routes of administration affect how well and how quickly a drug is absorbed:
1. Oral - Taken by mouth and absorbed through the digestive system.
2. Rectal - Administered through the rectum.
3. Topical - Applied directly to the skin or mucous membranes:
Skin - Applied on the skin surface.
, Oral mucosa - Absorbed through the tissues in the mouth, which includes:
Sublingual - Placed under the tongue for quick absorption.
Buccal - Placed between the gums and cheek.
4. Parenteral - Injected directly into the body, bypassing the digestive system:
Intravenous (IV) - Delivered directly into the bloodstream.
Intramuscular (IM) - Injected into a muscle.
Subcutaneous - Injected under the skin.
5. Inhalation - Breathed in through the lungs.
[2] Distribution: throughout body
After absorption into the bloodstream, drugs are distributed throughout the body – The key
factors influencing distribution are:
1. In the Blood (Albumin):
Albumin = blood protein that binds drugs.
Bound drug = inactive (can't cross cell membranes).
Free drug = active (can cross membranes and work).
The extent of binding depends on drug properties and albumin availability.
2. Types of Distribution:
Extracellular (Blood Plasma): This refers to the portion of the drug that stays within the
bloodstream – The drug will circulate in the blood plasma before potentially reaching various
organs and tissues.
Intracellular (Water in Body Cells): Some drugs enter the cells themselves, where they can
have their therapeutic effect – Drugs that can easily penetrate cell membranes will distribute
intracellularly.
3. Speed of Distribution → The speed at which a drug is distributed throughout the body largely
depends on its lipid solubility:
Lipid-soluble drugs (like heroin) can easily pass through cell membranes, which are made of
lipid layers – This allows them to distribute more quickly and efficiently into various tissues,
including the brain.
Water-soluble drugs (like morphine) have more difficulty crossing lipid membranes and tend
to be distributed more slowly.
, Why? Drugs move through the body via passive diffusion, meaning they naturally move from
areas of higher concentration to areas of lower concentration until equilibrium is reached.
Higher lipid solubility leads to faster distribution because the drug can easily diffuse
through the lipid-rich cell membranes, making it quicker to reach its target site.
[3] Metabolism: conversion by body
The body converts drugs, usually in the liver, into forms that are easier to eliminate. This can
involve transforming a drug into an active or inactive metabolite. Metabolism is crucial in
determining how long a drug will last in the body and how potent its effects are.
[4] Excretion: elimination from body
Drugs and their metabolites are eliminated from the body, primarily through the kidneys (in urine)
or liver (through bile and feces) – Efficient excretion ensures that drugs do not build up to toxic
levels in the body.
These are all key processes in...
Pharmacokinetics: The study of how the body Pharmacodynamics: The study of how drugs
processes drugs (absorption, distribution, affect the body (the mechanism of action, the
metabolism, excretion). therapeutic effects, side effects).
Pharmacokinetics:
Overview:
Refers to the changes over time in serum concentration of a drug and its metabolites.
Answers the question: How does the body process the medication?
Focuses on four key processes:
Absorption: How the drug enters the bloodstream.
Distribution: How the drug reaches different tissues and organs.
Metabolism: How the drug is broken down, often by the liver.
Elimination: How the drug and its metabolites exit the body, primarily through urine or feces.
Key Informations:
The drug's serum concentration changes over time as it is absorbed, distributed, metabolized,
and eliminated – Monitoring these concentrations helps determine the appropriate dosing and
timing of medications.
The entire blood circulation takes about 1 minute, which is a key factor in how quickly the drug
can be distributed throughout the body.
The body contains about 10 billion capillaries, with a total surface area of 200 m² – They are the
smallest blood vessels in the body and allow nutrients, gases, and drugs to diffuse into tissues.
, Every cell in the body is within 10-30 microns of a capillary, which ensures efficient nutrient,
gas exchange, and drug delivery. This means that drugs can quickly reach their target cells
through this efficient exchange system.
Pharmacodynamics:
Pharmacodynamics describes how a drug affects the body, focusing on its biochemical and
physiological effects and the underlying mechanisms of action.
Examines the relationship between drug concentration and its effect on the body.
Studies the dynamics of therapeutic effects, side effects, and toxicity.
Key Concepts:
Medication–Receptor Interaction:
Drugs bind to specific receptors (e.g., enzymes, ion channels) to exert their effects.
The nature of this interaction determines:
Pharmacological Effect: Desired therapeutic outcome.
Toxic Effect: Undesired or harmful side effects.
Plasma Concentration vs. Time Relationship:
Drug levels in plasma fluctuate over time, influencing its effects:
Therapeutic Range: Optimal concentration for effectiveness without toxicity.
Subtherapeutic Range: Concentration too low to produce a meaningful effect.
Toxic Range: Excessive concentration causing adverse effects.
This relationship highlights the importance of correct dosing to stay within the therapeutic
window.
Time–Concentration Dynamics: Describes how drug levels in the plasma change over time
following administration. Here's a breakdown:
At T₀ (Time Zero): Medication Administered:
Initial Event:
The drug is administered (e.g., orally, intravenously).
This causes a sharp increase in plasma concentration, creating a large peak.
Peak Plasma Concentration:
Reflects the maximum drug level in the bloodstream – It is influenced by:
Route of Administration: Intravenous administration results in immediate high
plasma levels, while oral drugs take time to absorb.
