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Flashcards in Mechanisms of Drug Action Deck (19)
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State the four types of drug antagonism.

Receptor blockade
Physiological antagonism
Chemical antagonism
Pharmacokinetic antagonism


What is meant by ‘use dependency’ in terms of receptor blockade?

This refers to ion channel blockers
The more the tissue on which a drug is acting is being used (i.e. the more active they are), the more effective the blocker will be


What is physiological antagonism?

When two drugs act on different receptors in the same tissue and have opposite effects


What is chemical antagonism?

Interactions of drugs in solution


What is pharmacokinetic antagonism?

When one drug reduces the concentration of another drug at the site of its action
A drug may reduce the absorption, increase the metabolism or increase the excretion of the other drug


Define drug tolerance.

Gradual decrease in responsiveness to a drug due to repeated administration of the drug


What are the five main mechanisms of drug tolerance?

Loss of receptors
Change in receptors
Pharmacokinetic factors
Physiological adaptation
Exhaustion of mediator stores


Describe each of these drug tolerance mechanisms briefly.

Loss of receptors – overstimulation can lead to endocytosis of receptors so there are fewer receptors available on the cell membrane
Change in receptors – conformational change in the receptors so that they are desensitized, so a proportion of the receptors are no longer effective
Pharmacokinetic factors – metabolism of the drug is increased after repeated use (e.g. alcohol)
Physiological adaptation – sort of like a homeostatic response to maintain a stable internal environment
Exhaustion of mediator stores – this happens with amphetamines –they get into the central noradrenaline synthesis system and replaces noradrenaline in the vesicles so you get a big increase in the production of noradrenaline


What are the four receptor families? Describe how their transmission varies.

Type 1 – ionotropic
Type 2 – metabotropic (G protein coupled)
Type 3 – tyrosine kinase linked
Type 4 – intracellular steroid type
They increase in transmission time from 1-4


Describe the structure of type 1 receptors.

Consists of 4 or 5 subunits with transmembrane alpha helices


Describe the structure of type 2 receptors.

Consists of 1 subunit but with 7 transmembrane domains


Describe the structure of type 3 receptors.

Single protein with 1 transmembrane domain
Inside the cell there is an intracellular domain
When the agonist stimulates the receptor it activates the catalyst


Describe the structure of type 4 receptors.

These are steroid receptors that are found in the nucleus


What is another name for the DNA binding domain of the steroid-receptor complex?

Zinc fingers


Example of chemical antagonism

Dimercaprol is a chelating agent that forms heavy metal complexes that are more easily excreted by the kidneys


Use of chemical antagonism

Anti venom


Example of physiological antagonism

Noradrenaline will bind to alpha-1 receptors and cause vasoconstriction, histamine will bind to histamine receptors and cause vasodilation


Example of receptor blockade

Normal neurons fire at a relatively low rate so if you put local anaesthetic on them there’ll be fairly limited effects. Nociceptor neurons fire rapidly so their iron channels are open more often meaning that the local anaesthetic can get inside the iron channel and block it more easily.


Example of each type of receptor

2- mAChR, adrenoceptors
3- insulin, GFR
4- steroid