3 - Drug Elimination/ Elementary pharmacokinetics Flashcards
2 examples of drugs with a low TPR
cardiac glycosides and barbiturates
TPR=
maximum tolerated conc / minimum effective conc
the greater the Kel of a drug the ____ the concentration of drug drops
faster
what is first order kinetics
the rate of elimination is directly proportional to the drug concentration
the higher the conc of a drug the __ the rate of elemination - with 1st order kinetics
greater
if the Kel is large the halflife is __
short
halflife is ____ related to Kel
inversely
t1/2 = ___/Kel
0.69
1st order kinetics - when a dose is doubled the __ and __ are not affected
Kel and T1/2
when you double the concentration what happens to the number of half lives?
one half life is added on
define clearance
- the volume of plasma cleared of a drug in unit time
- a constant relating the rate of elimination to plasma concentration
with 1st order kinetics
rate of elimination = ___ x ___
clearance x plasma concentration
clearnace is the constant
clearance determines the ____ ___ rate
maintenence dose rate
what are the units of clearance
L/hr
what is the rate of elimination?
the amount of drug being eliminated per unit time
Kel and rate of elimination are NOT the same thing
NOT
how do you figure out total clearance
add up the clearance at each of the clearance organs
steady state = rate of ___ = rate of ___
administration = elimination
CpSS = ___ /___
maintenence dose rate / CL
For drugs that exhibit first order kinetics, the steady state (ss) plasma concentration (Css) is linearly related to the _____ rate
infusion
the time to reach Css is determined by __ __ but NOT the ___ ___
half life, not the infusion rate
Css is reached after approx ___ half lives
5
how is Css calculated with oral dosing
Css =
(F x dose) / (Clp x dosing interval)
the amount of drug in the body (Ab) = ___ x ___
Vd x Cp (plasma conc)
for I.V administration loading dose = __ x ___ __
Vd x target Cp
for oral administration loading dose = (__ x ___ __ ) /__
(Vd x target Cp ) / F
what is half life dependent on?
Vd and clearance
half life =( 0.69 x __ ) /__
Vd/ Cl
zero order kinetics can occur when the plasma conc of a drug is ____ than the -__ of an enzyme that metabolises it
greater than the Km
