pharmacokinetics cop (mostly equations) Flashcards
how to calculate elimination rate constant from a graph
k= -(lnC2 - lnC1)/t2-t1
how to calculate half life
t1/2= ln2/k
what is the unit for elimination rate constant
h^-1 (or any per unit of time)
how to calculate the area under curve
AUC= dose/CL or dose/K x Vd
how to calculate clearance
CL= K x Vd
units for AUC
mg x h/L
how to find AUC on a graph
split graph into trapeziums
0.5(a+b)h for all then add conc of last/k
units for clearance
volume per unit time eg. ml/min, L/h
how to calculate clearance for IV bolus dose
CL= dose/AUC
how to calculate maintenance dose rate and units
maintenance dose rate (mg/h) = CL (L/h) x target concentration (mg/L)
how to calculate clearance for oral dosing
CL= (F x dose) /AUC
F=bioavailability
how to calculate clearance for intravenous infusion
CL = (R x Tinf)/AUC
R=rate of infusion
Tinf= duration of infusion
how to calculate volume of distribution (vd)
vd= total amount of drug in body/plasma drug concentration
units of vd
L (volume)
how to calculate what amount of drug to give
amount of drug to give= vd x plasma drug concentration required
(basically vd rearranged)
things that affect volume distribution
renal/liver failure, dehydration, age, weight
how to calculate vd for IV bolus dose on a graph
vd= dose/ C0
C0=conc at time zero
how to calculate vd with clearance and elimination rate constant
vd= CL/K
how to calculate vd for iv bolus
vd= dose / (AUC x k)
how to calculate vd for oral dose
vd= (F x dose )/ (AUC x k)
how to calculate vd for intravenous dose
vd= (R x Tinf )/ (AUC x k)
how to calculate vd with steady state concentration
vd = R/Css x k
Css= steady state conc
what is bioavailability (F)
fraction of administered drug that enters systemic circulation unchanged
how to calculate absolute bioavailability in non intravenous drugs
absolute bioavailability= (Dose intravenous x AUC non-intravenous) / (Dose non-intravenous x AUC intravenous)
what is the bioavailability of any intravenous drug and why
1, the absolute bioavailability equation compares non IV routes bioavailability with an IV one
how to calculate relative bioavailability and when to use it
relative bioavailability= (dose of formulation 1 x AUC of formulation 2) / (dose of formulation 2 x AUC of formulation 1)
use when IV data for bioavailability is not obtained
explain what happens when bioavailability of a drug increases (graph)
peak time and rate of decrease stats the same, higher plasma drug conc
why is bioavailability important
measures completeness of absorption of a drug
factors that affect bioavailability
route of administration, drug formulation, drug metabolism, drugs physical properties, drug interactions with other drugs/food, patient factors
how to calculate dose to give using absolute bioavailability
dose to give= dose in systemic circulation / absolute bioavailability
how to calculate dose in systemic circulation
dose in systemic circulation= dose given x absolute bioavailability
what is bioequivalence
when 2 drugs have similar bioavailability
equation using bioavailability, AUC, CL and dose
bioavailability= (AUC x CL)/dose
what is absorption rate constant (Ka) and its units
rate drug is absorbed from site of action into systemic circulation after administration
units= per unit time (eg. h^-1 or s^-1)
what does a larger Ka mean
faster absorption, higher plasma drug concentration, peak plasma conc will increase, time to reach peak decreases, time for drug to be cleared decreases
how to find absorption rate constant
Ka= ln2/t1/2 = 0.693/t1/2
how to find residual graph from a plasma conc/time graph
- extrapolate linear part to time 0
- find actual conc and extrapolated conc of each time (already linear bits stay the same)
- extrapolated-actual conc
- plot new concs on same axis and add line of best fit (residual graph)
straight=first order kinetics
how to find half life on a residuals graph
- choose any conc and its time
- half the conc and find the time
- t2-t1=t1/2
