ILA 3 - Pharmokintics And Pharmodynamics Flashcards
Define pharmacodynamics
Effect of drug on the body
Pharmokinetics
Effect of body on the drug
What is protein binding affect on the drug
protein binding lowers the free concentration of a drug
Should induction drug have low or high protein binding
Ideally the induction drug should have low protein binding to enable a high initial plasma concentration. If strongly protein bound then the plasma concentration of free drug will be lower.
Should induction drug have low or high lipid solubility
In order to put the patient to sleep quickly the drug should have a high lipid solubility in order for it to readily cross the blood brain barrier and reach its site of action
Why does the second drug after the IV drug have to be given?
With IV drug injection there is a high initial plasma concentration and the drug may rapidly enter well perfused tissue such as brain, liver & lungs…
The drug will continue to enter less well perfused tissues lowering the plasma concentration…
The concentrations in the highly perfused tissues then decrease.
This action is important in terminating some drugs given as a bolus e.g thiopentone produces rapid anaesthesia because of initial high brain concentrations, but is short lived as continued muscle uptake lowers the blood concentration & indirectly the brain concentration.
If a second anesthetic agent is not given then as the plasma concentration of thiopentone decreases the patient will start to wake up.
What is an agonist
Ligands that bind to a receptor and produce an appropriate response are called agonists, ie a drug that binds to and activates a receptor. Can be full, partial or inverse.
Define the three types of agonist
Full agonist: has high efficacy, producing a full response while occupying a relatively low proportion of receptors
- Partial agonist: has 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.
- Inverse agonist: produces an effect opposite to that of an agonist, yet binds to the same receptor binding-site as an agonist
Define antagonist
Ligands that prevent an agonist from binding to a receptor and thus prevent its effects are called antagonists, ie a drug that attenuates the effect of an agonist. Antagonists do not themselves have any pharmacological actions mediated by receptors.
Define competitive antagonist
Binds to the same site as the agonist but does not activate it, thus blocking the agonist’s action.
Define non-competitive antagonist
Binds to an allosteric (non-agonist) site on the receptor to prevent activation of the receptor.
What are the drug receptors and drug targets
Receptors, enzymes, transporters/carrier proteins, ion channels
Example of receptor for drug receptors
muscle relaxants are competitive antagonists of acetylcholine at the post synaptic nicotinic receptor. They block the receptor preventing ACh from binding and causing muscle contraction.
Example of enzymes for drug receptors
Angiotension-converting enzyme (ACE) inhibitors (eg Ramipril) block the conversion of angiotensin I to angiotensin II (a vasoconstrictor) this causes vasodilation which reduces blood pressure.
Transporters/carrier proteins
Proton pump inhibitors (lansoprazole) prevent the production of stomach acid (H+) by inhibiting the proton pump mechanism in the parietal cells. Example2: tricyclic antidepressants and catecholamine uptake
