Pharmacology Flashcards
define pharmacokinetics
what the body does to the drug (process of absorption and distribution)
what happens when a drug is administered?
absorbed into the blood stream to systemic circulation where it is distributed to tissues
define pharmacodynamics
the effects of the drug on the body
what happens when the drug reaches it’s site of effect?
there is pharmacological effect leading to the clinical response
what two effects are seen in the clinical response to a drug?
toxicity
therapeutic effect
what does toxicity describe in relation to clinical response to a drug?
the side effects
when may an animal be given a drug even when there are contraindications?
if the quality of life is sufficiently affected then a cost benefit analysis will indicate that it is worthwhile giving the drug
what are the 2 key ways in which drugs work?
non-cellular mechanisms
cellular mechanisms
what are the 4 main non-cellular ways in which drugs work?
physical effects
chemical reactions
physicochemical mechanisms
modification of body fluid composition
why do fluids work through non-cellular mechanisms instead of cellular mechanisms?
because the effects that they have on cells isn’t direct, it is instead mediated by osmosis that is caused by changes if fluid composition
give an example of a drug with physical effects
eye lubricant
give an example of a drug which works to modify body fluid composition
hypertonic saline
what are the 4 main cellular mechanisms in which drugs work?
physicochemical/biophysical mechanisms
cell membrane structure and function modification
enzyme inhibition
receptor mediated effects
give an example of drugs which affect cell membrane structure and function
insulin
give an example of drugs that work through enzyme inhibition
NSAIDs
give an example of drugs that work through receptro mediated effects
opioids
what are the targets for drug action?
receptors enzymes transporters ion channels nucleic acid miscellaneous
how may receptors aid drug action?
transduce signal from drug to produce conformational change and influence flow of ions
how can enzymes be affected by drug action?
may be activated or inhibited
how are ion channels affected by drug action?
open or close
how are transporters influenced by drug action?
carry a molecule across the membrane
give an example of receptors which are targeted by drugs
mu opioid receptor
give an example of enzymes which are targeted by drugs
COX 1 and 2
give an example of a drug that may be moved by transporters
insulin
give an example of a drug that affects ion channels
local anaesthetics
define ligand
a substance that forms a complex with a receptor (biomolecule) to serve a biological purpose (e.g. analgesia in the case of opioids)
what is the role of a receptor?
interacts with extracellular physiological signals and converts them to intracellular effects
describe the 3 step process involved in a receptor converting extracellular signalling to intracellular effects
receives a signal
transduces signal to
effector mechanism
what are the 2 ways receptors will be targeted by drugs?
agonist or inverse agonist
antagonist
what are the main effects of agonists/inverse agonists on receptors?
direct through ion channel opening or closing
transduction mechanisms leading to enzyme activation/inhibition, ion channel modulation and DNA transcription
what is an example of a receptor agonist/inverse agonist?
dexmedetomidine
what is the effect of antagonists on receptors?
prevents binding of other agonists/antagonists
produces no effect and blocks endogenous mediators
give an example of a receptor antagonist
atipam
what are the 2 effects of drugs on ion channels?
blockers
modulators
what is the effect of blockers on ion channels?
permeation blocked so no entry or exit
what is the effect of modulators on ion channels?
increased or decreased opening probability
where do modulators and blockers sit within ion channels?
blockers sit within the channel itself
modulators sit in the sub-unit
what are the 3 ways drugs can affect enzymes?
inhibition
false substrate
prodrug
how does a false substrate affect the enzyme?
is structurally similar to substrate but not the same so an abnormal metabolite is produced
how does prodrug worth with an enzyme?
makes use of the enzyme function to convert prodrug to active drug. An active drug is produced by the reaction
how do transporters work to produce drug effects?
normal transport to allow drug to enter cell
inhibition of transporter to block transport
false substrate leading to accumulation of abnormal compounds
what are the 4 main types of receptors?
ligand gated ion channels
G-protein coupled receptors
kinase linked receptors
nuclear receptors
what are the fastest acting receptors?
ligand gated (milliseconds)
what are the slowest acting receptors?
nuclear receptors (hours)
how do ligand gated ion channels work?
lead to hyperpolarisation or depolarisation and therefore cellular effects
how do G-protein coupled receptors work?
change in cell excitability leads to activation of second messengers which cause protein phosphorylation. This leads to cellular effects
how do kinase linked receptors work?
receptor phosphorylates protein leading to gene transcription, protein synthesis and then cellular effects
how do nuclear receptors work?
receptors in the nucleus cause gene transcription this then leads to protein synthesis and cellular effects.
give an example of a ligand gated ion channel
nicotinic ACh receptor
give an example of a G-protein coupled receptor
muscarinic ACh receptor
give an example of a kinase linked receptor
cytokine receptor (linked to inflammation)
give an example of nuclear receptors
oestrogen receptors
define affinity
how well/avidly a drug binds to it’s receptor
define intrinsic activity/ efficacy
magnitude of a drugs effect once bound (0-1)
what is a full agonist able to do once bound to the receptor?
generate a maximal response
describe the affinity and intrinsic activity of full agonists
high affinity and high intrinsic activity
give an example of a full agonist drug
morphine is a full agonist at the mu opioid receptor
what type of receptor is a mu opioid receptor?
G-protein coupled receptor
what is a partial agonist drug?
one that has intrinsic activity of less than 1
what does receptor occupancy of a partial agonist drug lead to?
a sub maximal effect even if receptors are fully bound
give an example of a partial agonist drug
buprenorphine binds to the mu opioid receptor but does not produce a maximal effect even if the dose is increased
what is an inverse agonist?
drug binds and exerts an opposite effect to the endogenous agonist
give an example of an inverse agonist
antihistemines
define antagonist
exhibits affinity but no intrinsic activity
give an example of an antagonist
atipam antagonises a-2 adrenoreceptor against dexmedetomidine
define potency
the dose of a drug required to produce a response (more potent = less drug required for response)
what is therapeutic index a measure of?
maximum non-toxic dose divided by minimum effective does
what is the issue with using therapeutic index?
based on data that may not be clinically relevant
effective dose can be extremely variable depending on what is being treated
doesn’t account for idiosyncratic reactions
what does ADME stand for?
absorption
distribution
metabolism
excretion
what is ADME involved with?
what the body does to the drug
why is it important that drugs can cross cell membranes?
to enable them to reach their site of action so they may have an effect
what are the 5 main ways that drugs cross cell membranes?
aqueous diffusion passive lipid diffusion facilitated diffusion pinocytosis active transport
what is the law which governs the rate of transfer of drug across biological membranes?
Fick’s law of diffusion
what are the 5 elements of Fick’s law of diffusion?
diffusion coefficient surface area of tissue membrane thickness partition coefficient concentration gradient
what is the partition coefficient?
how drugs distribute themselves in water vs in oil
what sort of molecules are drug molecules usually?
small weak acids or weak bases
what is the level of ionisation of a drug determined by?
pKa of drug and pH of the surrounding tissue
how do non-ionised drugs cross biological membranes?
passive diffusion
how do ionised drug molecules cross biological membranes?
selective transport mechanisms, facilitated diffusion or pinocytosis
what process in the body may affect drug absorption?
infection/inflammation can change tissue pH and make it more acidic
what is drug absorption mainly influenced by?
route of administration and drug formulation
peripheral shutdown if present
define bio-availability
the fraction of a dose reaching the systemic circulation after administration IM compared to the same does administered IV
what are the 8 key routes of drug administration?
IV IM SC oral inhalational epidural transmucosal (oral and rectal) transepithelial (skin, cornea, nasal mucosa)
where does drug absorption primarily take place after oral administration?
small intestine
what types of drug molecules are usually poorly absorbed through oral administration?
low lipid soluble and strong acids and bases
what are the 4 main factors which affect GI absorption?
gastrointestinal motility
splanchnic blood flow
particle size and formulation
physicochemical factors
how can gastrointestinal motility affect GI absorption of drugs?
fast and slow can mean that not enough of the drug is absorbed
how may splanchnic blood flow be reduced and so reduce drug absorption?
dehydration and reduced BP