Practical Flashcards
Occupancy?
[D]Ka / 1 + [D]Ka OR [L] / [L] + Kd OR [A]Ka / 1 + [A]Ka + [B]Kb
How many receptors are occupied when [D] = Kd?
Half
Dose ratio
1 + [A]k2
C bound = ?
K binding x C free x Cpp
Henderson Hasselbach equation?
pH - pKa = log [base]/[acid]
Vd = ?
total drug in body / plasma conc
Filtration rate or rate of excretion if not reabsorbed or secreted?
GFR x Cfree
Excretion rate if extensively reabsorbed?
Urinary flow rate x Cfree
Excretion rate if secreted?
Renal plasma flow x C
Rate of renal excretion?
C urine x V urine / t
Renal/hepatic clearance?
Rate of renal/hepatic excretion / plasma conc
Clearance from a Cp vs time graph?
Dose absorbed / AUC or dose rate / Css
Bioavailability from a clearance vs time graph?
AUC oral / AUC iv
Plasma conc for first order elimination?
Co x e ^ -ke x t
How to work out half time from a LnCp vs time graph?
0.693 / ke
How to work out AUC from a LnCp vs time graph if it is straight?
Co/ke or Css/ke
How to work out Vd from a LnCp vs time graph?
Clearance / ke
How to work out amount of blood in the body when an infusion stops?
Vxx x Css or clearance x AUC
Plasma concentration when approaching steady state?
Css(1-e^-ke x t)
Cmin at steady state?
Cmax x e ^ -ke x tau
Amount in body at start of dose interval?
Cmax x Vd
Amount in body at end of dose interval?
Cmin x Vd
Dose absorbed?
Vd(Cmax - Cmin)
Css?
dose rate x F / clearance or AUSss/tau
Loading dose / maintenance dose?
Css/Cav1
Dose rate?
Css x clearance / F
Total body water?
42L
Extracellular water?
14L
Intracellular water?
28L
Plasma water?
3L
Interstitial fluid?
11L
What is Vd the same as for a highly ionised drug?
ECF
What is Vd the same as for a plasma protein binding drug?
Plasma volume
How does phase I conjugation affect drugs?
More polar and easily extruded
Which B3 mutation reduces efficacy?
N265M within TM2
Which mutation blocks halothane and isoflurance?
S270W mutation in GABA alpha subunit
Which mutation reduces inhibition of NMDA receptor?
TM3/4
What is plotted on a Scatchard plot?
[BSp]/[L] against [BSp]
What is the gradient of a Scatchard plot?
-Ka
What is the x intercept of a Scatchard plot?
Bmax
What is plotted on a double reciprocal plot?
1/[BSp] against 1/[D]
What is the y intercept of a double reciprocal plot?
1/Bmax
What is the x intercept of a double reciprocal plot?
-K1
What do you plot to find Ka of an unlabelled drug with fixed radioligand conc?
IC50 against [radioligand]
What is the y intercept of an IC50 against [radioligand] plot?
1/Kunlabelled
What is the gradient of an IC50 against [radioligand] plot?
Klabelled / Kunlabelled
What do you plot to find how many molecules bind to a receptor?
log (response / max response - response) against log[drug]
What is the gradient of a log (response / max response - response) against log[drug] graph?
How many molecules bind
What is a heterotropic interaction?
Oppose each others effects
What is a homotropic interaction?
Transmitter bind to its own presynaptic autoreceptors
Which graph do you use to find the IC50 after a radioligand binding assay?
Mean dpm against log[BCh]
How to work out affinity constant using IC50, Kradioligand and [radioligand]?
[radioligand]Kradioligand + 1 / IC50
Clearance?
dose/AUC OR Vd x Ke OR rate of elimination/Cp or amount in body
C av?
dose rate / clearance
What is blood flow to liver?
1 litre per minute
What is Tau?
Dosing interval
Ka?
[DR] / [D] + [R]
Therapeutic dose?
LD50 / ED50
Ka of an unlabelled drug is both drugs are the same?
1 / IC50 - [radioligand]
Hill equation?
nlog[D] - logKdiss
[agonist] to shift EC50 twofold?
10 ^ -logKa2
What is affinity for agonist like in high GTP?
Low
How does GTP level affect antagonist affinity?
It doesn’t
What is GPCR affinity for agonist like in membrane preparations?
High (low GTP)
When will the Scatchard plot appear curved?
Two populations of receptors with different affinity contants and Bmax
What is homologous desensitization?
Only receptors which are stimulated become desensitised
What is heterologous desensitisation?
Receptors other than stimulated ones are desensitised - activates PKA which decouples alpha subunit of G protein
Why does heterologous desensitization not lead to endocytosis?
Arrestin does not recognise the PKA phosphorylated receptor seen in heterologous desensitization)
Why are hydrophilic radioligands used?
Can’t get to internal receptors AND endocytosis not initiated if they are an antagonist
Rate of decrease in concentration?
ke x concentration
What to do if working out fraction of concentration after a certain time?
C / C0 = the fraction, this is equal to e ^ -ke x t
How to work out Ke from a LnCp vs time graph?
- gradient
What does it mean if the lnC vs time plot os not a straight line?
There is redistribution into tissues - a two compartment model
What happens if urine is at a low pH?
Weak acids are more uncharged so more is reabsorbed from the kidneys - opposite for weak bases
What happens if urine is at a high pH?
Weak acid is less easily reabsorbed from the kidneys
What does a drug need in order to be secreted?
A transporter protein
What is the clearance if the drug is filtered AND secreted?
625 ml/min (renal plasma flow)
If first order elimination, what does doubling the dose do to the AUC?
Doubles it
What happens to the ratio of the dose to the AUC of clearance is constant?
The same - D2 / AUC2 = D1 / AUC1
Vd if lnCp vs time line is straight?
dose / C0
Vd if drug redistributes (called Vz)?
Clearance / Kz
Average conc at steady state?
DF / tau x CL
What is the difference between dose rate and tau?
Dose rate measured in amount per time, tau just time
Cmax - Cmin (concentration change?)
dose x F / Vd
Loading dose?
Vd x Cav,ss
clearance x C av,ss?
Dose rate
How to work out clearance from rate of infusion and Css?
Clearance = rate of infusion / Css
What is the process of homologous desensitization?
BARK phosphorylates the receptor, this increases affinity for B-arrestin, this uncouples the alpha subunit of the G protein
How to find number of receptors?
Multiply avogadro’s number by molar conc