Mechanisms of drug action Flashcards
What are the types of antagonism?
Receptor blockade
Physiological antagonism
Chemical antagonism
Pharmacokinetic antagonism
Define the types of antagonism?
Receptor blockade: Antagonist binding to receptor and preventing the binding of an agonist
Physiological antagonism: Two drugs act at different receptors to have opposite effects in the same tissue
Chemical antagonism: Interaction of drugs in solution (chelating agent)
Pharmacokinetic antagonism: When one drug reduces the concentration of the other drug at the site of its action
What term can be used to link receptor blockage and ion channel blockers? What does it mean?
Use dependency - The more the tissue, that the drug is acting on, is being used the more effective this type of blocker. Local anaesthetics - Nocireceptor neurones vs normal neurones
Give an example of physiological antagonism.
NA and Histamine affecting the vasculature.
NA binds to adrenoreceptors
What is a chelating agent and give an example?
A molecule which forms heavy metal complexes that are more rapidly excreted by the kidneys. Useful for lead poisoning. E.g Dimercaprol
Give an example where pharmacokinetic antagonism is important.
Barbiturates - microsomal enzymes
What are causes of drug tolerance?
Pharmacokinetic factors Loss of receptors Change in receptors Exhaustion of mediator stores Physiological adaptation - like a homeostatic response (body attempts to maintain a stable environment
Give an example of a drug that results in tolerance?
Benzodiazepines
Describe a pharmacokinetic factor that would result in drug tolerance
Metabolism of the drug increases when it is given repeatedly over a period of time
Alcohol and Barbiturates
How does the loss of receptors occur?
Membrane endocytosis - occurs when cell is repeatedly stimulated by an agonist. Receptor down regulation
What receptor is susceptible to down regulation?
Beta adrenoreceptors
What is meant by a change in receptors?
The receptors undergo a conformational change so a proportion of receptors are no longer effective. They undergo desensitisation.
What happens during an exhaustion of mediator stores?
This occurs with amphetamines. See notes for process of how amphetamines affect the body.
What are the different families of receptors?
Type 1 - Ionotropic receptor (ion channel linked) - milliseconds
Type 2 - G-protein coupled receptor (Metabotropic) - seconds
Type 3 - Tyrosine kinase-linked receptor - minutes
Type 4 - Intracellular steroid type receptors - hours
Give examples for all the types of receptors
Type 1 - Nicotinic acetylcholine receptor + GABA
Type 2 - Muscarinic receptor + beta 1 adrenoreceptors in the heart
Type 3 - Insulin and growth factor receptor
Type 4 - steroid/thyroid receptors
