Pharmacokinetics Flashcards
Drug enters plasma
absorption
Drug transported to and from sites of action
distribution
chemical structure of drug changed
biotransformation (metabolism)
irreversible loss of drug
excretion
loss of drug concentration or effect
elimination
Variable for volume of distribution
Vd
Variable for half-life
t1/2
Variable for elimination rate or constant
K or Ke
Variable for loading dose
LD
Variable for dose interval
T
Variable for steady state plasma concentration
Css
Variable for peak concentrations at steady state
Cmax
Variable for trough concentrations at steady state
Cmin
Decrease in drug concentration with respect to time
reaction rate
Manner in which reaction rate affected by drug concentration
reaction order
Reaction rate independent of drug concentration
zero order reaction
Slope of zero order reaction
constant and linear
Reaction rate dependent upon drug concentration
first order reaction
Units of first order reaction
reciprocal of time (hr-1)
Rate of elimination is higher at higher concentrations in this reaction
first order
Amount of time required for a drug concentration to fall 50%
Half-life
Half-life is reciprocally related to which reaction constant
first-order
Alcohol undergoes which order elimination
zero order
When an enzyme is saturated it catalyzes the reaction at
zero order
Ethanol is oxidized to acetaldehyde catalyzed by what enzyme
alcohol dehydrogenase
Characteristics of blood level vs time curve
rate and extent of absorption
rate and extent of distribution
rate and extent of metabolism
rate and extent of excretion
Parameters of blood level vs time curve
time of onset of action (latency)
time to peak drug effect
time of drug effect (duration of action)
area under the curve
therapeutic range or window
f: fraction of drug dose given orally that reaches systemic circulation
determinants of f: absorption and first pass metabolism
Metabolism of the drug prior to reaching the systemic circulation
First pass metabolism
Assumes instantaneous absorption and distribution
one compartment model
Has a distribution phase and an elimination phase
two compartment model
Rapid clearance from central to peripheral compartment
distribution phase of the two compartment model
overall elimination from central compartment
elimination phase of the two compartment model
Central compartments
heart
liver
lungs
kidney
blood
Peripheral compartments
fat tissue
muscle tissue
cerebrospinal fluid
Weak acids bind to
serum albumin
Weak bases bind to
glycoproteins
Plasma protein binding is
non-specific
Plasma protein levels change with
age and disease
Consequences of plasma protein binding
longer duration of action
displacement of bilirubin by sulfonamides will cause kernicterus (bilirubin encephalopathy; neurotoxicity)
drug-drug interactions; drug displacement
misinterpretations of drug levels
Drug binding to tissues
elevates apparent volume of distribution
Drug binding to plasma proteins
depresses apparent volume of distribution
Volume of plasma cleared per unit of time
drug clearance
Drug clearance is independent of
elimination mechanism
Steady state plasma concentration is achieved after
4 elimination half-lives
Level necessary to achieve steady state plasma concentration is dependent on
dose and dose interval
bioavailability and clearance
Time necessary to achieve steady state plasma concentration is independent of
dose and dose interval
Multiple dosage regimens graphed show
peaks and troughs
Peaks and troughs include
therapeutic windows
differences proportional to dosing interval and elimination half-life
Dose necessary to maintain steady state plasma concentration
maintenance dose
Loading dose allows
steady state concentrations to be achieved quickly
Larger initial one time dose given to quickly establish desired plasma level
Loading/priming dose
This disease can impact dug elimination
renal
Creatinine is neither absorbed or secreted so it reflects
glomerular function
Creatinine plasma concentration and clearance reflect
renal function
Creatinine clearance decreases, drug half-life increases for drugs dependent on
renal excretion (tetracycline)
