pharmacokinetics Flashcards
in order to induce anaesthesia quickly what characteristics should the drug have in terms of its protein binding?
Protein binding lowers the free concentration of a drug
Therefore high protein binding results in a low plasma concentration of free drug
Ideally want the drug to have low protein binding to enable a high initial plasma concentration
in order to induce anaesthesia quickly what characteristics should the drug have in terms of its lipid solubility?
drug should have a high lipid solubility in order for it to readily cross the blood brain barrier and reach its site of action
High lipid solubility leads to fast absorption and distribution
an anaesthetic (thiopentone) is given intravenously.
Explain in terms of the drug distribution of the intravenous drug why an additional volatile drug needs to be given as soon as the patient is asleep. What would happen if it were not given?
anaesthetic is administered IV therefore has 100% bioavailability
will be taken up by well perfused areas (ie. the brain) very quickly, leading to high initial brain concentrations, sending the patient to sleep
however this is short lives as other less perfused areas continuously take up the drug eg. the muscles
leaving less drug available for the brain
if no additional drug is given, patient will have muscle paralysis but brain would wake up
define agonist
a ligand that binds to a receptor to activate it and form a chemical-receptor complex
can be full or partial or inverse
define a partial agonist
drugs that bind to and activate a given receptor, but have lower efficacy than a full agonist.
It produces sub-maximal activation even when occupying the total receptor population, therefore cannot produce the maximal response, irrespective of the concentration applied.
give an example of an agonist and name its receptors
Adrenaline is an agonist at beta adrenoceptors
Opioids are agonists for opioid receptors in the brain
define an antagonist
a ligand that binds to a receptor to for a chemical-receptor complex. it does not activate the receptor, instead it reduces the effect of an agonist
(by preventing the agonist from binding to a receptor).
give an example if an a antagonist
propranolol, a β-adrenoceptor antagonist, binds to β-adrenoceptors in the heart and prevents catecholamine-induced tachycardia (for example in response to exercise).
define a competitive antagonist
directly competes with the agonist by binding to the same site and blocking its action. It inhibits, does not activate the receptor
define a non-competitive antagonist
Binds to an allosteric (non-agonist) site on the receptor to prevent activation of the receptor.
It does not completely block the effect of the agonist
are competitive antagonists reversible?
are they surmountable?
they are reversible and surmountable
ie. if you increase dose of agonist you can overcome (surmount) the antagonist
give an example of a competitive antagonist
naloxone (reverses effects)
= the Opioid antidote
give an example of a non-competitive antagonist
Ketamine at the NDMA-glutamate receptor,
memantine ( used to slow the progression of Alzheimer’s)
In addition to ‘receptors’ what three other drug targets are there?
receptors
enzymes
transporters
ion channels
give an example of a drug that targets and acts on receptors and explain how it produces its desired effect.
Muscle relaxants target receptors
These are competitive antagonists of ACh at the postsynaptic nicotinic receptor
They block the receptor, preventing ACh from, binding and causing muscle contraction
