pharmacokinetics cop (mostly equations)

Question 1

how to calculate elimination rate constant from a graph

Answer 1

k= -(lnC2 - lnC1)/t2-t1

Question 2

how to calculate half life

Answer 2

t1/2= ln2/k

Question 3

what is the unit for elimination rate constant

Answer 3

h^-1 (or any per unit of time)

Question 4

how to calculate the area under curve

Answer 4

AUC= dose/CL or dose/K x Vd

Question 5

how to calculate clearance

Answer 5

CL= K x Vd

Question 6

units for AUC

Answer 6

mg x h/L

Question 7

how to find AUC on a graph

Answer 7

split graph into trapeziums
0.5(a+b)h for all then add conc of last/k

Question 8

units for clearance

Answer 8

volume per unit time eg. ml/min, L/h

Question 9

how to calculate clearance for IV bolus dose

Answer 9

CL= dose/AUC

Question 10

how to calculate maintenance dose rate and units

Answer 10

maintenance dose rate (mg/h) = CL (L/h) x target concentration (mg/L)

Question 11

how to calculate clearance for oral dosing

Answer 11

CL= (F x dose) /AUC

F=bioavailability

Question 12

how to calculate clearance for intravenous infusion

Answer 12

CL = (R x Tinf)/AUC

R=rate of infusion
Tinf= duration of infusion

Question 13

how to calculate volume of distribution (vd)

Answer 13

vd= total amount of drug in body/plasma drug concentration

Question 14

units of vd

Answer 14

L (volume)

Question 15

how to calculate what amount of drug to give

Answer 15

amount of drug to give= vd x plasma drug concentration required
(basically vd rearranged)

Question 16

things that affect volume distribution

Answer 16

renal/liver failure, dehydration, age, weight

Question 17

how to calculate vd for IV bolus dose on a graph

Answer 17

vd= dose/ C0

C0=conc at time zero

Question 18

how to calculate vd with clearance and elimination rate constant

Answer 18

vd= CL/K

Question 19

how to calculate vd for iv bolus

Answer 19

vd= dose / (AUC x k)

Question 20

how to calculate vd for oral dose

Answer 20

vd= (F x dose )/ (AUC x k)

Question 21

how to calculate vd for intravenous dose

Answer 21

vd= (R x Tinf )/ (AUC x k)

Question 22

how to calculate vd with steady state concentration

Answer 22

vd = R/Css x k

Css= steady state conc

Question 23

what is bioavailability (F)

Answer 23

fraction of administered drug that enters systemic circulation unchanged

Question 24

how to calculate absolute bioavailability in non intravenous drugs

Answer 24

absolute bioavailability= (Dose intravenous x AUC non-intravenous) / (Dose non-intravenous x AUC intravenous)

Question 25

what is the bioavailability of any intravenous drug and why

Answer 25

1, the absolute bioavailability equation compares non IV routes bioavailability with an IV one

Question 26

how to calculate relative bioavailability and when to use it

Answer 26

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

Question 27

explain what happens when bioavailability of a drug increases (graph)

Answer 27

peak time and rate of decrease stats the same, higher plasma drug conc

Question 28

why is bioavailability important

Answer 28

measures completeness of absorption of a drug

Question 29

factors that affect bioavailability

Answer 29

route of administration, drug formulation, drug metabolism, drugs physical properties, drug interactions with other drugs/food, patient factors

Question 30

how to calculate dose to give using absolute bioavailability

Answer 30

dose to give= dose in systemic circulation / absolute bioavailability

Question 31

how to calculate dose in systemic circulation

Answer 31

dose in systemic circulation= dose given x absolute bioavailability

Question 32

what is bioequivalence

Answer 32

when 2 drugs have similar bioavailability

Question 33

equation using bioavailability, AUC, CL and dose

Answer 33

bioavailability= (AUC x CL)/dose

Question 34

what is absorption rate constant (Ka) and its units

Answer 34

rate drug is absorbed from site of action into systemic circulation after administration units= per unit time (eg. h^-1 or s^-1)

Question 35

what does a larger Ka mean

Answer 35

faster absorption, higher plasma drug concentration, peak plasma conc will increase, time to reach peak decreases, time for drug to be cleared decreases

Question 36

how to find absorption rate constant

Answer 36

Ka= ln2/t1/2 = 0.693/t1/2

Question 37

how to find residual graph from a plasma conc/time graph

Answer 37

1. extrapolate linear part to time 0 2. find actual conc and extrapolated conc of each time (already linear bits stay the same) 3. extrapolated-actual conc 4. plot new concs on same axis and add line of best fit (residual graph) straight=first order kinetics

Question 38

how to find half life on a residuals graph

Answer 38

1. choose any conc and its time 2. half the conc and find the time 3. t2-t1=t1/2