Principles of Pharmacology Flashcards
Define a drug
any substance which interacts with a biology system and changes it
what is pharmacology?
the study of the mechanism of drug action
what are the characteristics of most drugs?
Their effects occur at very low concentrations –> Potency
Drugs can be very specific –> Biological/chemical specificity
Drugs can compete for their receptors
What is an example of a pharmacological investigation?
The isolated ileum preparation
what is the receptor concept?
Drugs produce their effects by combining with specific receptors sites in cells. The response is a function of the number of occupied receptors,
What is an agonist in pharmacological terms?
Binds to a receptor and produces a response.
Therefore it poses both affinity and efficacy.
What is an antagonist in pharmacological terms?
Binds to a receptor but do not produce a response. Competitive antagonists prevent agonists binding and so bloc the response to an agonist. Therefore it poses affinity but not efficacy.
Come in various different types (competetive, irreversible, other)
What is affinity of a drug?
A measure of how well it binds to the receptor.
What is the efficacy of a drug?
A measure of the degree to which an agonist produces a response when binding a given proportion of receptors.
What is a Full Agonist?
A drug with an efficacy of 1
What is a Partial Agonist?
A drug that cannot produce the cells maximal response, even when they have bound to all available receptors since they have low efficacy
A drug with an efficacy of less than 1 but >0
What is an Inverse Agonist?
Bind to agonist receptors but produce an opposite response
A drug that can inhibit any intrinsic receptor activity (ie. prevents a protein from changing shape) that might exist in the absence of any ligand.
Has a negative efficacy ( one <0)
what is quantitative pharmacology?
based on the assumption that drugs act by entering into a simple chemical reaction with certain receptors in cells and that there is a simple relation between the amoun of drug fixed by these receptors and the action produced.
What is the law of mass action?
A + R <=> AR
point of equm (Kd) is the dissociation constant
How can you work out Kd from the law of mass action equation?
Kd = [A][R] / [AR]
units mol/litre
How can you calculate the fixed number of receptors?
Rt = [R] + [AR]
How can you calculate the occupancy of a drug?
p = [AR] / [Rt] (p = occupancy) (Rt = fixed no of receptors; Rt = [R] + [AR])
What is the Langmuir Isotherm equation and what is it used for?
p = [A] / (Kd + [A])
This equation can be theoretically used to determine the amount of drug bound to a receptor.
what is the spare receptors concept?
The idea that some highly efficacious agonist can produce a maximal response from a cell without binding to all available receptors.
Show how an agonist affects the path between the agonist and the receptor.
A + R AR AR* –3–> EFFECT
(1) - affinity governs binding
(2) - Through binding activates the drug
(3) - efficacy governs activation
Show how an inverse agonist may affect the path of a reaction
A + {R} R AR AR —-> EFFECT
(1) - affinity governs binding
(2) - efficacy governs activation
What are some drug targets (binding sites)?
Enzymes - cyclooxygenase (the aspirin receptor)
Ion channels - Nifedipine blocks Ca2+ ion channels
Transporters (pumps) - cocain blocks noradrenaline transporters
Physiological receptors - receptors for hormones or neurotransmitters
How can you regulate cell function with drugs?
altered cell membrane potential
altered enzyme activity
altered gene expression
drugs can target these things directly to produce their effects
most drugs effect these cells via physiological receptors
How are receptors classified?
Classified on the basis of the selective action of drugs
Named according to the neurotransmitter or hormone with which they interact
Most transmitters/hormones interact with more than one type of receptor - the differences in protein structure underlie the different subtypes
