4. Principles of drug action Flashcards
What is pharmacology?
It is the study of interacts between chemicals and living systems.
What are drugs?
Drugs are chemical substances which, by interacting with biological systems, are able to change them in some way. Drugs have effects example: contraction of muscles, secretion by glands, release of hormones.
What are the properties of an ideal drug? (EECSSRPFL)
- Effective
- Ease of administrations
- Chemical stability
- Safety
- Selectivity
- Reversible action
- Predictability
- Freedom from drug interaction
- Low cost
What is a receptor?
A target molecule through which physiological mediators (neurotransmitters, hormones) produce their effect.
Site of action for drugs?
Receptors
Class of receptor?
Protein
Location of receptors?
Plasma membrane- on cell membrane surface.
What is a signaling molecule and what does it bind to?
Ligand is a signaling molecule
It binds to specific receptors
Role of receptors
Used by cells to send signals either intracellularly or extracellularly.
True or false: Ligand has more than 1 receptor?
True- ligand has a choice of which receptor to bind to
What is the macroscopic effects?
When there is a large population of receptors (e.g., within the membrane of a cell), any given ligand molecule has a choice of receptors with which to bind. In this case, the interaction follows a set pattern called the dose-response curve.
What is a dose- response curve?
Represents the relationship between drug concentration and drug effect. Y-axis shows the response/effect. X axis shoes the dose.
On the dose- response curve, what does the following mean: E and Emax?
E: Effect
Emax: Maximal effect
What is seen when a dose-response curve is plotted on a log scale?
The curve has a sigmoidal curve shape
What is E50% on the log dose-response curve?
This is the summary value that gives half-maximal effect
What does it mean that a drug has specificity?
Receptor and ligand fit like a lock and key: specificity is a function of the ligand’s shape and the receptor’s binding site.
Receptors show high level of ligand specificity, explain
2 different ligands may be able to bind to the same receptor but how tightly they bind and how long they remain bound may be different.
What is meant by affinity?
How well a drug binds to a receptor
What is Kr and Kf in the rate constant equation?
Kr- forward rate constant
Kf- backward rate constant
This 2 rate constants are used to calculate the equilibrium constant.
What is Kd?
Equilibrium constant
This is the concentration of drug required to occupy 50% of sites at equilibrium.
Kd also relates to the concept of affinity
How is affinity calculated?
Relationship between affinity and Kd?
AFFINITY= 1/Kd
Affinity is how well a drug can bind to a receptor.
Drugs that bind tightly how a low equilibrium constant
Agonist meaning
Drugs that bind to receptors and do initiate a response. Activate receptors and produce subsequent responses.
Antagonist meaning
Drugs that bind to receptors and do not initiate a response. No activation, occupy the receptor and blocking.
Potency meaning
Refers to the quantity of drug that must be administered to produce a specific effect.
Agonist potency depends on what 2 parameters?
Affinity and Efficacy
What is the efficacy for antagonists and agonists?
Antagonists: Efficacy is 0
Agonists: Efficacy is significant
Synonym of efficacy?
Intrinsic activity
Meaning of affinity and efficacy?
Affinity: tendency to bind to receptors.
Efficacy: ability, once bound, to initiate changes that lead to effects.
Affinity describes?
How well a ligand will bind to its receptors
Efficacy describes?
How well a ligand will stimulates a receptor
True of false; affinity and efficacy are largely independent of each other?
True
Dose- response curve provides information about?
Efficacy and potency
Characteristics of a good potent drug?
Most potent drug: lower dose required to produce a big response
What is meant when a drug is selective??
Means drugs ability to preferential produce a particular effect
True of false: drugs can be selective or non-selective?
True
Which neurotransmitter is released by cholinergic fibres vs adrenergic fibres?
Cholinergic fibres: Ach
Adrenergic fibres: NE
On the dose- response curve, what is measured along the horizontal axis vs the vertical axis?
Horizontal axis: Potency
Vertical axis: Efficacy
