Drug receptor interactions Flashcards
What is the definition of a drug?
A chemical substance that interacts with a biological system to produce a physiological effect
What are the 4 different drug target sites?
Receptors
Enzymes
Ion Channels
Transport Systems
Where are most receptors found?
They are exposed on the cell surface so drugs can easily get to them
What is the exception to the where most receptors are found?
Steroid receptors are found in the nucleus
What are examples of receptor affecting drugs? Name an agonist and an antagonist
Ach (agonist)
Atropine (antagonist)
How are receptors activated?
NT or hormones
What are examples of drugs that affect ion channels?
LA (local anaesthetic)
Ca2+ Channel Blockers (-dipines)
What are the two types of ion channels?
Voltage sensitive (VSCC) Receptor linked nAChR (nicotinic acetylcholine receptor)
What are ion channels?
Selective pores that allow transfer of ions down an electrochemical gradient
What are transport systems?
They transport against a concentration gradient eg glucose uptake into cells, ion transporters and neurotransmitters
What are example of drugs that affect transport systems
Tricycle antidepressants TCAs
Cardiac glycosides
What is an example of what TCAs do?
They can slow down the NA reuptake and deactivation therefore allowing longer time for noradrenaline action to take place.
What are enzymes
Catalytic proteins that increase reaction rate
What are examples of drug interactions with enzymes?
Enzyme inhibitors eg anticholinesterase
False substrates eg methyldopa
Prodrugs eg chloral hydrate or trichoroethanol
What is similar within receptor families and how many families are there?
They have similar structures and transduction systems. There are 4 families
What are examples of non specific drug actions?
Antacids - all basic eg Mg/Al hydroxide
Osmotic purgatives - draw water into gut
What are non specific drug actions for?
Treating patients using the physiochemical properties of the drug
What does plasma protein binding react to a drug and what is the result?
The drug binds to albumin and causes the inactivation of the drug, providing a reservoir of inactive drug. There is no physiological reaction and is used as drug storage within the body
What is an agonist?
A ligand - any substance that binds to and stimulates a receptor eg ach or nicotine
What is an antagonist?
Something that binds to a receptor but doesn’t cause a reaction therefore blocks the receptor and decreases activity eg atropine or hexamethonium
What does the potency of a drug depend on?
Affinity
Efficacy
What does affinity mean?
The binding property of a receptor
What does efficacy mean?
The ‘intrinsic activity’ to do smth to generate a response eg conformational change of a receptor
What is a full agnonist
It can generate the full response of a receptor
What is a partial agonist
It can never generate the full response of a receptor
What happens when you use a partial and a full agonist at the same time?
Partial agonist will generate a slight antagonist effect
What is selectivity?
The degree to which a drug acts on a given site relative to other sites
Why is the term selectivity used instead of specificity?
Because specificity means it binds to only one receptor but in high enough doses, a drug will bind to several different receptors and cause some of the unwanted side effects of drugs
What is the key factor of an antagonist that is different to agonists?
Antagonists have affinity but no efficacy
What are the 2 types of receptor antagonists
Competitive and Irreversible
What is the key property of a competitive antagonist?
It binds to the same site as the agonist, and is therefore surmountable (if high conc agonist then it can overcome the antagonist)
How can you see surmountable on dose response curve?
D-R curve shift to right
What are examples of receptor antagonists?
Atropine
Propranolol (beta blocker)
What is the key property of an irreversible antagonist?
If do bind to same site as agonist, binds more tightly than the agonist. OR binds at a different site. Both are insurmountable (and drugs last longer)
What is an example of an irreversible antagonist?
hexamethonium
