Pharmacology Flashcards
What is phamacodynamics and pharmacokinetics?
Pharmacodynamics is the effect of the drug on the body
Pharmacokinetics is the effect of the body on the drug (ADME)
What is druggability or ligandability?
The ability of a protein target to bind small molecules.
How well a biological target can impacted by a drug.
What are the four kinds of receptor which may be druggable?
Ligand gate ion channels
G protein coupled receptors
Kinase-linked receptors
Cytosolic/nuclear receptors
What is a GPCR made of and how do they work?
Ligand binds to a receptor site among the 7 transmembrane proteins.
This activates a G protein which alpha subunit (attached to the transmembrane proteins) binds GTP turning it on.
This releases the beta-gama dimer along the plasma membrane which activates adenyl cyclase etc.
When ligand is removed, GTP is hydrolysed to GDP and the beta-gamma dimer returns to the alpha subunit
Name 2 common enzymes which G protein activate
Adenylyl cyclase - cAMP
Phospholipase C - IP3
How do kinase linked receptors work?
Ligand binds to extracellular part
This allows phosphorylation of the intracellular domain
This causes intracellular cascade
How do nuclear receptors work?
Ligand passes into nucleus to ligand binding domain
Causes transcription of certain proteins which act as transcription factors on other parts of the genome.
For a receptor agonist, what is EC50?
Effective dose 50 - what amount/concentration of a drug will give 50% of the maximum response
Describe potency?
What makes a drug more potent than another?
This relates to whether a drug is strong or weak
If drug A causes a greater response at the same dose of drug B, then drug A is more potent.
What is a full agonist?
An agonist which can reach a 100% response - even if a very large dose is required.
What is a partial agonist?
Where no matter how much agonist we give, it cannot reach 100% response. The maximum it reaches is called Emax.
What is Emax of a partial agonist?
The maximum response of a partial agonist
What is efficacy? What would make a drug more efficacious?
This relates to how effective the drug is, independent of dose. If drug A has a higher Emax than drug C, it is more efficacious.
What is the difference between efficacy and potency?
Potency relates to whether a drug is strong or weak. If we need double dose for same effect, it is half as potent.
Efficacy is do to with how effective a drug is - can you get a maximal response or not?
What is the intrinsic activity of a compound?
Intrinsic activity is a measure of the ability of a drug that is bound to the receptor to generate an activating stimulus and produce a change in cellular activity.
It is similar to efficacy
What is the calculate for intrinsic activity (of drug X)?
Intrinsic activity = Emax of partial agonist (X) / Emax of a full agonist
What is affinity?
This describes how well a ligand binds to the receptor. This is property shown by both agonists and antagonists
What 2 “tissue related” factors govern drug effect?
Receptor number - other drugs can completely block receptors
Signal amplification - the amplitude can vary greatly.
What 2 receptor related factors govern drug affect?
Affinity of receptor
Efficacy of receptor
What is receptor reserve?
When an agonist only needs to activate a small fraction of existing receptors to produce a maximal response, there will be spare receptors.
As such, if you give irreversible antagonists there may not be any affect at low doses as you are just blocking the receptor reserve.
What is allosteric modulaton?
Where you activate or block a receptor using a different site to where ligands bind.
What is inverse agonism?
When a drug binds to the same receptor as an agonist but causes the opposite response - like a form of antagnoism
What is tolerance?
Drug tolerance
Repeat exposure to a drug means the receptors become desensitised and you do not get the same response.
What is densitisation?
Give 3 ways desensitisation occurs
Where receptors stop producing a great affect. Receptors can be
Uncoupled to enzymes
Internalised (conformation changes)
Degraded
You need a greater dose for the same response.
Are drugs specific or selective?
Selective - no compound is every truly specific and will act on a few receptors.
We are trying to change this
Pharmacokinetics Absoprtion:
What are four ways a drug can corss a membrane?
1) Passive diffusion across lipid bilayer (rate is proportional to concentration gradient, area and permeability (IVP to thickness))
2) Diffusion through ion channels - limited to small molecules
3) Carrier mediated transport, example of carrier is ATP-binding Cassette
4) Pinocytosis
Where are weak acid and weak base drugs best absorbed each?
Weak acids - stomach
Weak bases - intestine
Each will be unionised making them more lipid soluble so they can cross the phospholipid bilayer
How can we make Aspirin overdose be cleared quicker from the urine?
Alkalise urine.
Aspirin is a weak acid, hence by alkalising urine we can assure that it is ionised, and so will remain in urine
What 5 things do we need to consider when evaluating how well a drug reaches circulation from oral administeration?
1) Drug structure - lipid soluble improves. Also not being pH sensitive or targetted by digestive enzymes in SI
2) Drug formulation - A tablet that dissolves quickly?
3) Gastric emptying - can be slowed
4) Enzymes in intestinal lumen/wall
5) First pass metabolism
What is first metabolism and why can it be a problem/yield higher drug doses?
Where a drug is absorbed in the intestine, enters portal (venous) circualtion, is taken to the liver and is metabolised.
We lose drug if it is metabolised in the liver before reaching the systemic circulation
What kind of drugs can be absorbed transcutaneously?
Lipid soluble drugs. Also potent, non-irritant. E.g. Fentanyl patch
Why do we inject a drug subcutaneously?
It is absorbed more slowly than injected into a vein (e.g. long term contraceptive implants)
Also useful for local effects (e.g. anaesthetics)
What is a depot IM injfection?
Where a drug is made lipophilic before injected intramuscularly, this causes the drug to be absorbed into the blood slowly over weeks if necessary.
What required quality of a drug limits inhalational administeration?
We cannot deliver non-volative drugs (needs to be a gas).
Alternatively we can give them as a gas.
How does drug distribution change overtime when injecting IV?
(hint: osmolarity)
1) Initially there is a high plasma concentration of the drug, it moves out by osmosis, particularly to well perfused tissue such as the brain, liver and lungs
2) The drug continues to enter less well perfused tissues lowering plasma concentration
3) The high concentrations in well perfused tissues acts as a resevoir and drug moves back into blood by osmosis.
How can protein binding act as a drug depot?
If a drug binds reversibly to a plasma protein (commonly albumin) then when plasma concentration decreases, drug can release from protein
Note any drug irreversibly bound is effectively eliminated
Which kind of drugs can cross the placenta?
Small molecules - even these rarely reach feotal circulation as placenta blood flow is quite low.
What does the body (liver) try to do with lipid soluble drugs?
Tries to make lipid soluble soluble drugs more hydropholic so they can be excreted in urine.
Sometimes this can increase biological activity if a pro-drug is given.
Describe Phase 1 reactions/metabolism in the liver
Makes the drug more polar by unmasking or adding functional groups.
Oxidation is most common, usually catalysed by CYP450s (exceptions are alcohol dehydrogenase)
Describe Phase 2 reactions/metabolism in the liver
This is conjugation, adding a polar molecule via a covalent bond to make the molecule much more water soluble.
Name 3 different routes drugs can be excreted?
1) Fluids - urine, bile, sweat, tears, breast milk. Important for low molecular weight polar compounds
2) Solids - Important for high molecular weight compounds. Taken by hepatocytes and excreted in bile (note some can be reabsorbed in enterohepatic circulation)
3) Gases - important for volatiles