Pharmacokinetics Flashcards
Pharmacokinetics refers to?
using mathematical models to quantitative the time course of drug absorption and disposition in man and animals
what does rate refer to?
how fast the mass (dose) of a drug changes per unit time (mg/min)
what does the extent refer to?
how much of the mass (dose) of a drug changes in total
rate and extent describe the
flux of a drug within a system
What is a one-compartment model?
consider the body as consisting of a single, homogeneous compartment.
Volume of this theoretical compartment would equal the volume of distribution (Vd)
What is a 2 compartment model?
one central compartment (blood stream) where the drug is added and a secondary compartment to which the drug distributes.
usually has to get back into Blood Stream to be eliminated
What is the primary method for which pharmacokinetic parameters are determined in Vet Med?
Non-compartmental (stochasitc) models
Non-compartmental models provide important pharmacologic parameters in terms of statistical moments like.
the Mean Residence Time ( represents the avr. amnt. of time any given molecule of drug stays in the body)
What is population pharmacokinetics?
allows studies of large numbers of animals with less individual sampling.
What can population pharmacokinetics help do?
development of parameters for a drug that would apply to all breeds, ages, gender, etc.
What is Allometric scaling?
uses data on multiple species to try to predict the behavior of a drug in a species for which the info is unknown.
When are non-liner models used?
when drugs follow zero order kinetics.
What is Bioavailabilty (F)?
the fraction of a given dose which finds its way into circulation
how is Bioavailabitly (F) calculated
from the Area under the plasma concentration curve (AUC) expressed in proportion to the AUCiv (bc a drug that is given IV is 100% in systemic circulation)
what is bioequvalance?
different formulations of the same drug are bioequivalent when they are absorbed to a similar extent and similar rate Cmax and Tmax have to be similar
What is Half-life (t1/2)
the time required for a drug concentration to decrease by one-half or (50%)
what type of drugs dont follow 50% half life?
zero-order kinetic drugs will have a half-life dose that varies
what drugs will follow 50% half life?
drugs that follow 1st order kinetics, half-life will not change regardless of dose
what is zero order elimination?
the AMOUNT of drug eliminated per unit time is fixed. regardless of plasma conc.
what is first order elimination?
the Proportion of drug eliminated per unit time is fixed. rate of elimination depends on plasma concentration
the majority of veterinary drugs follow what order of elimination?
first order at therapeutic doses
compartment or stochastic models work well for predicting pharmacokinetics
what does the slope of elimination give?
Gives the Kel (elimination rate constant)
After 1 half-life the drugs is ____% gone.
50%
After 2 half-life the drugs is ____% gone.
75%
After 3.3 half-life the drugs is ____% gone.
~90%
After 5 half-life the drugs is ____% gone.
~97%
What is Plasma Concentration at steady state (CPss)?
the concentration at which the amount of drug going in ( repeated dosing or CRI) is equal to the amount going out (clearance CLb)
How do you measure therapeutic drug monitoring (TDM)
choose a particular time of the ay and always measure it at that same time (EX. 4 hr after morning pill)
What is the apparent volume of distribution (Vd)
the theoretical volume a drug would occupy if it was evenly distributed throughout the body at the same concentration as in plasma.
what does a very low Vd suggest?
the drug is not being distributed to all the tissue
What does a very high Vd suggest?
suggests that the drug is distributiong preferentially to tissue and may even be sequestered somewhere.
what is a high Vd?
Vd > 1L/kg
what is a low Vd
Vd < 1L/Kg
What is total body clearance (CLb)
the volume of distribution of drug in the body cleared of the drug per unit time (mL/min/kg)
CLb equals the
CLr + CLh + CLo = CLb
As Vd increases T 1/2 ______
increases
as clearance increases T1/2 ______
decreases
As Vd decreases T 1/2 _____
gets shorter
As Clearance decreases T1/2 ____
gets longer
What is the abbreviation for Volume of distribution?
Vd
What is the abbreviation for bioaviliblity?
F
What is the abbreviation for area under the plasma concentration curve?
AUC
what does Cmax stand for?
maximum plasma conc.
what does Tmax stand for
the time at which Cmax is reached.
what is Kel?
elimination rate constant (slope of elimination)
What is CPss?
plasma concentration steady state
what does Cp stand for
concentration in plasma
What is the abbreviation for total body clearance?
CLb
