Introduction to pharmacokitentics 2 Flashcards
2 main kinetic properties of drugs
first order
zero order
first order drugs
rate of elimination proportional to Cp
percentage of the total amount of the Cp change remains constant over time
its blood level drops the same percentage every time interval–even though the amount lost is smaller each time
zero order drugs
saturable (max) can’t metabolize after a certain amount
percentage of total amount of the Cp change is not constant
lose the same amount each time interval–not the same percentage
onset?
time it takes to get the MEC (minimal effective conc)
IV-onset of activity is shorter–hits MEC faster
TMax?
time it takes to get to Cmax
duration of action?
where drug is effective (MEC to MEC)
CMax?
highest conc of drug in blood–no more absorption
peak
Cmin?
lowest concentration of drug in patient that occurs before the next dose is given
dosing interval is 1 of key things that indicates Cmin
MEC
minimal effective conc
lowest plasma conc that becomes effective
MTC
maximal therapeutic conc
if above–toxicity occurs
therapeutic range
between MEC (minimal effective conc) and MTC (maximum therapeutic conc)
F
bioavailability Fraction of a dose that enters circulation extent of absorption F=1 for IV route no units
determines bioavailability
ionization status, first pass, dissolution
F=AUCoral/AUCivx100
S
salt factor
represents percentage of a dose that equals primary serum assessed drug
no units
3 items determining amount of drug absorbed
dose, bioavailability (F) and salt factor (S)
Vd
volume of distribution–units is L
volume of compartment necessary to account for total amount of drug in body and drug conc in plasma
not a physiologic value
represents extent of drug distribution
bigger value of Vd means what?
larger body distribution the more places the drug goes to/goes out of bloodstreams
blood volume in our body is 5 L
IBW
ideal body weight–units–kg
female=45kg +(2.3kgx inches above 60 inch)
Male=50 kg + (2.3 kg (height over 60 inch)
Adj body weight
adjusted dosing body weight–for actual BW>40% than IBW
Adj BW= 0.4x (ABW-IBW)+IBW
Cl–what is it? units?
units is L/hr
have to multiply its weight to book value
volume of blood per unit of time that is cleared of drug
Tau
units=hrs
represents dosing interval
if q8h then tau=8
Kel
elimination rate constant–units–x^hrs
a function of clearance
percentage of drug removed per unit of time
T1/2
half-life–units is hrs
time required for 50% of drug to be eliminated (blood conc to lower by 50%)
Cpss
steady state–units w/v
equilibrium between drug and body where Rate in=Rate out
time dependent
how long for pts to develop steady state?
4-5 half lives of the drug
At CPss what occurs?
DD/DL
if double the dose at steady state, you double the level of blood
Amount of drug absorbed formula
(S)(F)(Dose)
Loading dose
(Vd)(Cpdesired)/(S)(F)
Supplemental Loading dose
(Vd)(Cpdesired-Cpinitial)/(S)(F)
Clearance (Cl)
(S)(F)(Dose/Tau)/(Cp)
Maintenance Dose
(Cl)(Cp)(Tau)/(S)(F)
Elimination rate constant (Kel)
(Cl)/(Vd)
Half life (t1/2)
0.693/(Kel)
Creatinine Clearance (eGFR)
[(140-age)XIBW (in kgs)]/(72xSCr)
x0.85 if pt is female
Dose of diff dosage Form=
Amt (mg) Absorbed for current form/[(S)(F) of New Dosage form)]
Concentration in plasma (Cp)=
(S)(F)(Dose)/Vd
