mechanisms of drug action Flashcards
Define pharmacodynamics.
Effect of drug on body relating to mechanism of action.
Give 4 examples of drug target sites.
- Receptors,
- Ion channels,
- Transport systems,
- Enzymes.
(proteins)
What are receptors?
What activates them?
What do agonists and antagonists do + examples.
How many types of receptors?
Proteins within cell membranes (normally)
Activated by NT or hormone.
Agonist stimulate, antagonist inhibit. ACh = agonist, atropine = antagonist
4 types
What are ion channels?
Outline 2 types.
2 examples of drugs that act on ion channels.
Selective pores - allow ion transfer down electrochemical gradient.
- voltage sensitive (e.g. VSCC).
- receptor-linked (e.g. nAChR)
e. g. local anasthetics and Calcium channel blockers.
What is a transport system.
What do they transport (examples)
Drug examples.
Transport substances against their concentration gradient.
Specific for certain species.
e.g. Na+/K+ ATPase antiporter.
drug examples: tricyclic anti-depressants (TCAs), cardiac glycosides.
What are enzymes?
Outline 3 ways drugs interact with enzymes + examples.
Catalytic proteins - increase rate of reactions
Drug interactions -
1) enzyme inhibitors
e. g. anticholinesterases (neostigmine)
2) false substrates
e. g. methyldopa
3) prodrugs
e. g. chloral hydrate ® trichloroethanol
Can have unwanted effects. e.g. paracetamol.
How else might drugs bring about their effect?
physiochemical properties
e.g. antacids (basic substances that reduce stomach pain since they’re basic)
osmotic purgatives (draw H2O into gut - softening stools + aiding passing. work because of aformentioned physiochemical properties.
How can reservoirs of inactive drugs form?
Plasma protein binding (PPB)
How do antagonists inhibit function?
Blocking action of agonist. Bind + do nothing
What determines drug potency?
Affinity - ability to bind
Efficacy (‘intrinsic activity’) - action once bound (e.g. conformational change in receptor)
What’s the difference between a full and partial agonist?
How can a partial agonist act as an antagonist?
A full agonist can illicit a full response, partial agonists can never generate 100% of a response.
In the presence of a full agonist.
Define selectivity.
Degree of preference of drug for target receptor: overlap onto different receptors (especially at higher conc.)
Explain the structure-activity relationship.
The structure of a drug is directly related to its activity.
Small changes in drug structure can effect efficacy/affinity and its pharmokinetics.
Draw a dose-response curve comparing full and partial agonists.
+ the logarythmic equivalent.
Outline antagonist affinity and efficacy.
high affinity, no efficacy.
What are the 2 types of receptor antagonist?
+ examples
- competitve: same site as agonist, surmountable, shift D-R curve to right
e. g. atropine, propranolol - irreversible: bind tightly/at different site, insurmountable.
e. g. hexamethonium.
Draw a logarythmic curve comparing tissue response against log[Agonist] including competitve/irreversible antagonist.
