8. Drugs & Receptors Flashcards
How is concentration in grams per litre calculated?
Molarity x molecular weight
How is molarity calculated?
Grams per litre/molecular weight
What is the binding of a receptor governed by?
The affinity of the ligand and receptor
What is activation of a receptor governed by?
The intrinsic efficacy
What is efficacy?
The cell and tissue independent factors between a ligand binding and a response
Agonists have: affinity and efficacy? affinity only? efficacy only? none?
Agonists have both affinity and efficacy
Antagonists have: Affinity and efficacy? Affinity only? Efficacy only? None?
Antagonists have only affinity
How can drug receptor binding be measured?
Radioligands
What is Bmax?
The maximum binding capacity
What is Kd?
The dissociation constant, it is a measure of affinity
Measured as the concentration of drug at half max occupancy of receptors
A high Kd means what?
A low affinity for the receptor
A drug receptor binding curve on a logarithmic x axis will give you what graph shape?
Sigmoidal
How do you measure the EC50 and what does it represent?
Effective concentration giving 50% of the max response
This shows potency which is a combination of affinity and efficacy
Which has greater affinity for Beta 2 receptors, salbutamol or salmeterol?
Salmeterol
What enhances the utility of salbutamol?
Inhaled directly into the lungs hence straight onto beta 2 receptors
What is the problem with giving asthma drugs IV?
Salmeterol cannot be given IV, salbutamol can but has poor selectivity for beta 2 receptors, hence it agonises beta 1 as well, speeding up the heart.
Less than 100% receptor occupancy giving a 100% response leads to what?
Spare receptors
Does number of receptors have an effect on potency?
Yes
What is a partial agonist?
A drug that cannot produce a maximal effect even with full receptor occupancy
Can a partial agonist be more potent than a full agonist?
Yes as potency is dependant of affinity and efficacy
What is buprenorphine used for?
Buprenorphine is a partial agonist which has higher affinity but lower efficacy than the full agonist morphine. This means it can be used to out compete morphine with less of the respiratory depression that opioids cause.
What is IC50?
The concentration of antagonist that gives 50% inhibiton
What is naloxone?
High affinity opioid antagonist which is used to reverse respiratory depression as it will displace other opioids
What does the agonist response graph look like with increasing amounts of irreversible competitive antagonist?
Shifts it to the right as spare receptors are filled, then down as there are insufficient receptors for a full response
What is phenoxybenzamine?
Irreversible alpha 1 adrenoreceptor blocker used in hypertension episodes in pheochromocytoma
Name a non competitive antagonist used to analgesia
Ketamine
