Pharmacodynamics Flashcards
pharmacodynamics
effects of drugs on the body
- drug receptors
- dose/response curves
- mechanisms of drug actions
pharmacokinetics
effects of the body on drugs
- absorption
- distribution
- metabolism
- elimination
receptor
a specific molecule in a biological system that plays a regulatory role. Receptor interacts with a drug and initiates the biochemical events leading to drug effects
inert binding site
a component of the biologic system to which a drug binds without changing any function
ligand
in pharmacology, a molecule like a hormone or a drug, which binds to a receptor
covalent bonds
irreversible; drug removal/receptor reactivation requires re-synthesis of the receptor or enzymatic removal of the drug
non-covalent bonds
reversible; most drugs bind to receptors via non-covalent bonds
relative strengths of noncovalent bonds
ionic bond > hydrogen bonds > hydrophobic interactions
affinity
how readily and tightly that drug binds to its receptor
high affinity
good drug-receptor interaction; less drug needed to produce a response
low affinity
poor drug-receptor interaction; more drug needed to produce a response
Kd
equilibrium dissociation constant; drug concentration at which 50% of the drug receptor binding sites are occupied by the drug
lower Kd
higher affinity of a drug for the receptor
higher Kd
lower affinity of a drug for a receptor
selectivity
a property of a drug determined by its affinities at various binding sites
- measured by comparing affinities of a drug at different receptors
- a more selective drug would affect fewer targets over a certain concentration range
intrinsic activity
the ability of a drug to change a receptor function and produce a physiological response upon binding to a receptor
agonists
bind to the receptor and stabilize it in a particular conformation (usually the active conformation) producing a physiological response ((intrinsic activity))
antagonists
bind to the receptor but do not change its function. They prevent the activation of the receptor in the presence of an agonist.
- Do NOT have intrinsic activity
- no pharmacological effect in the absence of an agonist
full agonists
fully activate receptors, produce a maximal pharmacological effect when all receptors are occupied, maximal intrinsic activity
partial agnoists
partially activate receptor upon binding, produce a sub-maximal pharmacological effect when all the receptors are occupied
inverse agnoists
produce an effect opposite to a full or partial agonist; decrease receptor signaling; decrease response at receptors
*intrinsic activity is present and related to the inhibition of receptor function
pharmacologic antagonism
action at the same receptor as endogenous ligands or agonist drugs
chemical antagonism
when chemical antagonist makes the other drug unavailable
physiologic antagonism
occurs between endogenous pathways regulated by different receptors
competitive antagonists
compete with endogenous chemicals or agonist drugs for binding of the receptor; can be displaced from the receptor by other drugs
noncompetitive antagonists
receptor inactivation is not surmountable
irreversible antagonists
irreversibly bind to and occlude the agonist site on the receptor by forming covalent
allosteric antagonists
bind to a site other than the agonist site to prevent or reduce agonist binding or activation of the receptor
competitive antagonism on dose-response curve
Agonist ED50 increases, Emax does not change (more linear graph)
noncompetitive antagonism on dose response curve
agonist Emax decreases, EC50 does not change (more hyperbolic graph)
dose response curve
the relationship between a drug and its effects is described quantitatively (drug dose on x-axis/effects on y-axis)
what does a dose response curve look like if you plot it arithmetically?
hyperbolic curve
what does a dose/response curve look like if you plot the logarithmic version?
sigmoidal curve
what is Emax
the maximal effect that can be produced by the drug
what is ED50
the effective dose 50. The dose of drug that produces 50% of its maximal effect
graded response
- the MAGNITUDE of the response
- typically a mean value within a population or person
quantal response
- binary
- response or no response
- requires a pre-defined response (falling asleep, etc.)
- used to examine frequency of response
quantal dose response curve
relate dose of a drug to the frequency of response within a population
noncumulative quantal dose response curve
number or % of individuals responding at a dose of a drug and only at that dose
cumulative quantal dose response curve
number or % of individuals responding at a dose of a drug AND at all doses lower than that dose
TD50
median toxic dose
LD50
median lethal dose
therapeutic index formula
TI = TD50/ED50
*higher the TI, the safer the drug
therapeutic window
the range of doses of a drug or of its concentration in a bodily system that provides for the safe and effective therapy
wide therapeutic window
safer?
narrow therapeutic window
more dangerous?
potency
describes the amount of drug required to produce a specific pharmacological effect
- high affinity for receptor tends to be more potent
- lower ED50 more potent
efficacy
the maximal pharmacological effect that a drug can produce
- equivalent to Emax
- greater Emax, more efficacious the drug
Five major classes of drug targets
membrane receptors nuclear receptors ion channels transport proteins enzymes
signal transduction
the process by which cells transmit, receive, and respond to information from their environment and from each other
Components of signal transduction
1) ligand
2) receptor
3) intracellular signaling mechanisms within the target cell
protein kinases
modify protein by covalently attaching phosphate group to an amino acid residue
i.e. tyrosine kinases, serine-threonine kinases
phosphorylation
changes conformation of the protein, its activity, binding to other proteins, or localization within the cell
transcription factors
proteins that bind to specific DNA sequences and thereby control the transcription of the genetic information from DNA to RNA
specific action of transcription factors
activate or repress the recruitment of RNA polymerase to specific genes by binding to promoter regions of DNA (DNA sequence they bind is called the response element)
what is the defining feature of transcription factors?
have DNA binding domain
G protein coupled receptor structure
N terminal is extracellular
C terminal intracellular
7 transmembrane domain
Has alpha, beta, gamma subunits–> alpha dissociates with GTP when activated by ligand
Gs protein family and target
Gs –> adenylyl cyclases–> AC activation
Gi protein family and target
Gi –> adenylyl cyclases –> AC inhibition
Gq protein family and target
Gq –> phospholipase C –> PLC activation
G12/13 protein family and target
G12/13 –> Rho GTPases –> cytoskeletal rearrangements
Desensitization of GPCR
A reduced cAMP response is observed in the continued presence of agonist. This desensitization occurs within a few minutes. Removal of agonist for a short amount of time can lead to resensitization
Key signaling molecules in cAMP second messenger pathway
hormone receptor –>
stimulatory G protein –> adenylyl cyclase–>
phosphodiesterases that hydrolyze cAMP and cAMP dependent kinases with regulatory and catalytic subunits
role of phosphodiesterase
regulates cAMP to 5’-AMP
what is downstream of phospholipase C in G protein signaling?
IP3 and DAG
IP3 leads to release of calcium which binds to calmodulin
What do receptor tyrosine kinases generally transmit signals for?
growth factors (IGF-1, insulin, VEGF, EGF, NGF, PDGF)
general pathway of RTK activation
1) binding of growth factor
2) two receptors convert to active dimeric state by binding non-covalently
3) cytoplasmic domains of RTK are phosphorylated on Y subunit
4) phosphorylation of substrate proteins
receptors coupled to janus kinases (JAKs)
hormones and cytokines
- growth hormone (somatotropin)
- erythropoietin
- leptin
- interferons
- interleukins 2 to 10, 15
JAK STAT pathway
1) form dimeric structure upon binding cytokine/ligand
2) JAK (protein tyrosine kinase) molecules are activated
3) phosphorylation of signal transducers
4) activation of STAT molecules
5) STAT molecules travel to the nucleus where they regulate transcription
nuclear receptors
ligand activated transcription factors that modulate gene expression
- produce effects after a lag period
- effects can persist after the agonist concentration has been reduced to zero
ligands of nuclear receptors
lipophilic molecules that are able to cross the cell membrane
- steroid hormones
- thyroid hormones
- vitamin D, vitamin A
- free fatty acids