8 Drugs and Receptors Flashcards
What is the equation for Molarity?
Molarity (M) = g/L
——————–
Molecular weight
What type of receptor is a popular target for drugs?
GPCR
What is a drug ‘agonist’?
A ligand that causes a response so has both affinity and intrinsic efficacy.
What is a drug ‘antagonist’?
A ligand that binds to a receptor without producing a response. They only has affinity with NO intrinsic efficacy.
Define ‘affinity’
Affinity is the ability of a ligand to bind to a receptor
Define ‘intrinsic efficacy’
Intrinsic efficacy is the ability of a ligand to cause a response when bound to a receptor.
What is Kd?
Kd is the dissociation constant of a drug. It is a measure of affinity.
The lower the Kd, the higher the affinity.
What is the E50?
The effective concentration giving 50% of the maximal response. It is a measure of potency depending on both affinity and intrinsic efficacy.
What are the problems in treating asthma with B-adrenoreceptor agonists?
The therapeutic target is B2-adrenoceptors which causes bronchodilation. However the drugs also bind to other B-adrenoceptors which have side effects such as increasing the heart rate.
List the factors that determine the potency of a drug
Affinity
Intrinsic Efficacy
Cell/Tissue dependent factors
Define the term ‘spare receptors’
A spare receptor is when a 100% response of a drug is reached without filling all the available receptors therefore leaving some spare.
What is the purpose of spare receptors?
Spare receptors increase the sensitivity to a drug as responses can be generated at low concentrations of agonist.
What is ‘up-regulation’ of receptors and when does it occur?
Receptor numbers are increased with low activity.
What is ‘down-regulation’ and when does it occur?
Decreasing the number of receptors occurs when there is high activity.
What is a ‘partial agonist’?
A agonist that cannot produce a full response even with all receptors occupied.
Name a clinically used partial agonist
Opioids
What is ‘withdrawal’?
Withdrawal results in the opposite to acute drug effects. It occurs when a patient stops taking a drug they have been on for a long time.
Explain how drugs can reduce the effects of withdrawal
A partial agonist can act as an ANTAGONIST for a full agonist.
Eg. Buprenorphine has a higher affinity than heroin for the same receptors. The receptors become saturated with Buprenorphine so the effects of heroin are not felt.
When can partial agonists act as full agonists?
If the number of receptors increases enough to produce a full response
Reversible competitive antagonism
i. ) What happens when the antagonist is present?
ii. ) Is the inhibition surmountable?
iii. ) Give an example
i. ) The antagonist compete with the agonists for binding
ii. ) Yes
iii. ) Naloxone is a competitive antagonist at u-opioid receptors
Irreversible competitive antagonism
i. ) What happens when the antagonist is present?
ii. ) Is the inhibition surmountable?
iii. ) Give an example
i. )The antagonist competes for the binding sites but does not dissociate from the receptor
ii. ) No
iii. ) Phenoxybenzamine-non-selective is an irreversible a1-adrenoceptor blocker
Non-competitive antagonism
i. ) What happens when the antagonist is present?
ii. ) Is the inhibition surmountable?
iii. ) Give an example
i. ) Antagonist binds to an allosteric site on the receptor
ii. ) Varies
iii. ) NMDA receptor is a ligand-gated ion channel. Ketamine can bind intrinsically.
