pharmacokinetics Flashcards
pharmacokinectics
quantitative expression of relationship between absorption, distribution and elimination of drugs as a function of time
the effect of the drug is related to what
blood [drug]
One compartment model
drug rapidly equilibrates between plasma and tissue relative to elimination rate
semi-log plot of [plasma] over time, describe graph when drug follows first order kinetics for one-compartment model
straight line with
changes in [plasma] reflects proportional change in concentration of drug where
tissue
does drug distribute to all tissues
no
how long does it take for drug to equilibriate in 2-compartment model
longer
what are the two compartments in the model
central and peripheral
in 2 compartment model, where does elimination occur
central compartment.
what are the 2 phases in semi-log plot when drug follows first order kinetics for 2 compartment model
initial distribution
elimination phase
definition of elimination kinetics first order
rate of decrease in [drug] is directly proportional to the amount of drug in body
elimination kinetics first order, what fraction of the drug is eliminated
constant
most drugs follow what order of kinetics
first
define elimination rate constant (ke)
fraction of drug removed at any given time is constant and independent of dose
semi-plot for one compartment first order kinetics will look like
straight linear line
define zero order for elimination kinetics
constant amount of drug eliminated independent of dose
describe the enzymes involved in zero order elimination kinetics
saturated
define bioavailability
fraction of unchanged drug reaching systemic circulation after drug administration
drugs administered by intravenous route have a bioavailability of what
1
all other routes besides IV of administration have a bioavailability of
less than or equal to 1
what letter represents bioavailability
F
how is bioavailability determined after IV or other administration
measure [plasma] as function of time
name two drug examples for 0 order kinetics
asprin
alcohol
graph of 0 order kinetics on linear graph
linear line
The area under the curve (AUC) vs. time for bioavailability plots indicates what
index of extent of drug that enters the bloodstream and thus the body
for oral administration, bio-availabilty indicates what
extend of absorption and/or first pass effect
define half-life elimination
time needed for a 50% decrease in [ drug plasma]
half-life is expressed in units of
time, hours
equation for half life for 1 compartment model when Ke is known
.693/ke
half life can be used to measure what
how long it takes for a drug to be totally eliminated from body
four half lives rule
following 4 half lives, 94% of drug is eliminated and 6% remains in body
equation for fraction of drug elminated from body
= 1- 1/(2)^n
equation for fraction of drug remaining in body
1/(2)^n
definition for volume of distribution
apparent volume that a drug would be distributed within once an equilibrium is established with plasma
units for volume distribution
liters/kg
what type of volume is volume of distribution
apparent volume
large volumes of distribution are indication of a drug that is
highly lipophilic or low protein binding
formula for volume distribution
Dose(iv)/ C0
volume of distribution can be graphically determined by using what
plasma concentration at time 0
define clearance
volume of plasma from which a drug is totally removed per unit of time
units for clearance
L/hr or ml/mn
formula for clearance
CL - (Ke)(Vd)
What is half life of a drug dependent on
clearance and Vd
can you use half life along to predict Vd or CL
no
assuming single drug administration, [plasma] is directly proportional to what
dose of adminstration
formula for calculating amount of drug (A)
A = (C)(Vd)
formula for bioavailitbility (F)
AUC oral/ AUC iv
if taking drug a second time, how much total drug is in the body
amount of second dose will be added to amount remaining from first dose
concentration at steady state (Css) is defined as
average [plasma] maintained at Stead state
when Css attained
after 4 half lives
flucations between peak and trough and dependent on what
dosing interval
longer the dosing interval, what happens to peak and trough
greater variation ini peak and trough values
formula for Css
= MD (maintaned dose)/ Cl
Maintained dose (MD)
(Dose)(F) / (Dosing interval)
what is Css for constant IV infusion
Css = (infusion rate) / (CL)
define loading dose
single large dose to produce immediate rise in [drug plasma]
formula for loading dose
(Css)(Vd) / (F)
dosing interval will have the greatest effect on which parameter for a drug which follows first order kinetics
peak and troughs
to obtain stead state of a drug, what is it dependent on
half life
