BMS 113 · Common Core (Tronc commun)Section 1.2 · Introduction to pharmacology
Section 2 of 31
The language of pharmacology
Define drug, pharmacokinetics, pharmacodynamics, pharmacotherapeutics, toxicology, chemotherapy and pharmacopoeia, and use them correctly.
New to this course? How each section works
Learn gives you one short idea at a time. Each idea starts with a single sentence, then explains it, gives an example, and asks you a small question you can answer straight away.
Explore shows a diagram of the same ideas. Click the numbered parts to read what each one is.
Check asks a few questions. Answer them all correctly to finish the section and unlock the next one.
“Go deeper” is optional. It adds mechanism and extra detail for when you are ready — nothing you need for the checks is hidden there.
Why this matters
Almost every sentence in this course uses one of these words, so a learner who mixes them up will misread the lessons that follow. Confusing pharmacokinetics with pharmacodynamics, for example, sends you to the wrong explanation when a treatment fails. Learning this vocabulary now makes every later unit faster to follow.
What you need to know first
You need only the idea from Unit 1.1 that pharmacology is the science of drugs and living systems, plus everyday words such as dose, tablet and blood. Unit 1.1 also places pharmacology beside pharmacy, and this section builds its vocabulary on that base.
Words to know (5)
Drug
Any chemical substance that alters or modifies a biological function in a living organism. Paracetamol is a drug because it changes how the body handles fever.
Pharmacokinetics
The study of what the body does to a drug: absorption, distribution, metabolism and excretion. A tablet being absorbed through the gut wall is a pharmacokinetic step.
Pharmacodynamics
The study of what a drug does to the body, including its effects and its mechanism. Aspirin blocking an enzyme to relieve pain is pharmacodynamics.
Toxicology
The science of poisons, including the harmful effects of drugs. Studying the liver injury caused by an overdose is toxicology.
Pharmacopoeia
An official book of standards describing drugs and how to test their identity, purity and strength. The British Pharmacopoeia is used to check that a medicine meets its standards.
One idea at a timeIdea 1 / 4
In one sentence In pharmacology, a drug is any chemical substance that changes how a living organism works.
A drug is any substance that changes biological function
This broad definition includes substances used to diagnose, prevent, control or cure disease. The everyday word “drug” often means an illegal substance such as cannabis, heroin or cocaine, but the pharmacological meaning is much wider, and it overlaps with the word medicine. A medicine is a drug prepared and given for a therapeutic purpose; a poison is a substance that causes harmful or fatal effects.
For example
The same molecule can be a medicine at one dose and a poison at another: paracetamol treats fever at 500 mg and destroys the liver in large overdose.
Think of it like
A drug is like a key that fits a lock somewhere in the body, and a medicine is that key cut and given for a purpose. The image has a limit: many drugs do not turn one lock but change several processes at once.
Pause and check yourself
Does the pharmacological word “drug” mean only an illegal substance?
Show the answer
No. In pharmacology it means any chemical that changes a biological function; the narrow everyday sense covers only illegal substances.
Read detailed explanations
Why ADME is the backbone of dosing
Every dose schedule is a bet about ADME. Absorption decides how fast concentration rises. Distribution decides which tissues see the drug and whether it accumulates somewhere unwanted, such as fat for fat-soluble drugs. Metabolism decides how quickly the drug is inactivated, and is the reason grapefruit juice, which blocks a liver enzyme, can raise the level of some drugs to toxic range. Excretion decides how quickly the drug and its breakdown products leave; a patient whose kidneys are failing clears some drugs slowly and needs a reduced dose. Two numbers summarise the whole journey. Bioavailability is the fraction of the dose that reaches the general circulation unchanged; it is 100% for a drug given directly into a vein and lower for oral drugs that must survive the gut wall and the liver. Half-life is the time for half of the drug to leave the body; it sets how often a dose is needed. A drug with a long half-life can be given once daily; one with a short half-life may need several doses or a slow-release formulation.
Receptors: why tiny doses can matter
Many drugs act by binding to receptors — protein structures that normally receive signals from the body’s own messengers. A drug that copies the messenger is an agonist; one that blocks the messenger is an antagonist. This explains why doses are measured in milligrams or even micrograms: the drug does not need to flood the body, only to occupy a small number of very specific sites. It also explains selectivity and side effects. A drug will cause unwanted effects when it binds to a target other than the one intended, or when the intended target is present in more than one tissue. Atropine, for example, dries gut and airway secretions by blocking the same type of receptor that also controls the pupil and heart rate, so blurred vision and a fast pulse can accompany its intended effect. This is not carelessness by the prescriber; it is the direct consequence of receptor biology and a reason to warn patients in advance.
Explore the diagram
Look at the whole drawing first. Then select one numbered part and connect it to the idea you just read.
Pharmacokinetics and pharmacodynamics
The same drug journey seen from two sides: what the body does to the drug (ADME) and what the drug does to the body (effect at the target).
New to diagrams? Read this first
Look at the whole drawing once without clicking anything. Ask yourself only: what kind of picture is this (a comparison, a route, a sequence, a table)?
Press Play, or use the arrows, to move through the numbered parts in order. The drawing stays still; only the highlight moves.
Click a number, or its name in the list below, to read what that part is and why it matters. Use “Hide labels” when you want to test your memory.
More controls
01 / 6Absorption
If the drawing is wider than this panel, scroll it sideways. Labels stay readable; the numbered explanations below show the same ideas.
Absorption
Movement of drug from the site of administration into the bloodstream. It determines how quickly the effect begins. Oral drugs must first dissolve, then cross the gut wall; a drug placed directly into a vein skips this step.
Guided schematic: the numbered highlight moves; the drawing stays still. Not to scale.
Key points to remember
✓A drug is any chemical substance that changes a biological function; a medicine is a drug given for a therapeutic purpose.
✓Pharmacokinetics is what the body does to the drug: absorption, distribution, metabolism and excretion.
✓Pharmacodynamics is what the drug does to the body, through targets such as receptors and enzymes.
✓Pharmacotherapeutics, toxicology, chemotherapy and pharmacopoeia each name a different part of drug study and use.
Go deeper
Worked example
Separating PK from PD in one case. A patient is given a 500 mg paracetamol tablet for fever. Four hours later the fever has fallen. A second patient takes the same tablet and reports stomach discomfort. You are asked to label each observation as pharmacokinetic or pharmacodynamic.
The tablet dissolves and is absorbed through the gut — a pharmacokinetic step (the body acting on the drug).
The liver changes part of the drug before it reaches the general circulation, reducing the amount available — also pharmacokinetic.
The drug acts on the temperature-regulating centre and the fever falls — a pharmacodynamic effect (the drug acting on the body).
The kidneys clear the drug and its metabolites — again pharmacokinetic, and the reason the dose is repeated rather than taken continuously.
Pharmacokinetics describes the drug’s journey and how much of it arrives; pharmacodynamics describes what it does once it arrives. A weak effect may mean too little drug arrived (PK) or a target that did not respond (PD).
Common misconception
Beginners often think pharmacokinetics means “how the drug works”. It does not. PK is about the body handling the drug; how the drug works is pharmacodynamics.
Check your reasoning
A patient says the antibiotic “did not work”. Which pharmacokinetic and which pharmacodynamic explanations should you consider before assuming resistance?
Reveal an answer
Pharmacokinetic: the patient vomited the dose, took it with food that reduced absorption, or stopped early, so too little drug reached the infection. Pharmacodynamic: the organism may be genuinely resistant, or the drug may not reach that tissue. Checking both prevents blaming resistance by default.
Where this comes from
BMS 113 General Pharmacology I lecture notes · Unit 1.2, pp. 6–7
Lesson progress is saved on this device for the current learner. Practice answers stay separate and are not stored.
About this course and its sources
Bilingual lessons organised from the supplied BMS 113 General Pharmacology I lecture notes. Diagrams are original educational schematics; pharmacology, nursing and French-language review are pending.