Pharmacokinetics Flashcards
Pharmacokinetics
Use of mathematical models to quantitate the time course of drug disposition in man and animals
Allows us to evaluate the rate and extent of ADME
Rate
Refers to how fast the mass (dose) of a drug changes per unit time (mg/min)
Extent
How much the mass (dose) of a drug changes in total
Metabolism + Excretion = ?
Elimination
Remember, she said she would give us the formulas. We just need to know how to apply them.
:) isn’t that just dandy
Area under the curve (AUC)
measure of drug exposure
Bioavailabillity (F)
Fraction of the given dose which finds its way into systemic circulation
** Calculated from the AUC
What are some pharmacokinetic models?
- Compartment model
- Non-compartmental model (stochastic)
- Population pharmacokinetics
- Allmetric scaling
- Non-linar models
What model views the patient as a number of compartments?
Compartment model
What are the three types of compartment models?
One-compartment model
Two compartment model
Multi-compartment model
What model involves using statistical analysis of large numbers of actual animal data and is the PRIMARY method by which pharmacokinetic parameters are now determined in veterinary medicine?
Non-compartmental (stochastic)
What model estimates pharmacokinetics by looking at populations?
Population pharmacokinetics
What model uses pharmacokinetic data in multiple species to try to predict the behavior of a drug in a species for which this information is unknown?
Allometric scaling
What mode is used when drugs follow zero-order kinetics?
Non-linear models
What three things are important for an optimum dosage regimen?
Effective
No toxicity
No drug residues
Bioequivalence
Different formulations of the same drug are bioequivalent when they are absorbed to a similar extent and similar rate
Half- Life (t1/2)
The time required for the drug concentration to decrease by one-half (50%).
- Will be constant with first-order elimination (does not depend on dose)
Zero- Order Elimination
The amount of drug eliminated per unit time is fixed, regardless of plasma concentration
First- Order Elimination
The proportion of drug eliminated per unit time is fixed and the rate of elimination is dependent upon plasma concentration
The rate will change over time, but will do so in predictable way
What are some examples of drugs that use zero-order elimination?
- Phenylbutazone in horses
- Acetaminophen in cats
- Phenytoin in dogs
When saturation occurs, the clearance _____ (increase/decrease) and the half- life ________ (increase/decrease) which can lead to drug accumulation and potential toxicity.
clearance decreases
half-life increases
After 1 half-life ___ (%) of the drug is gone. 2 half-lives? 3.3 half-lives? 5 half-lives?
1 half-life = 50% of the drug gone
2 half-lives = 75%
3.3 half-lives = 90%
5 half-lives = 97%
Apparent volume of distribution (Vd)
The theoretical volume a drug would occupy if it was evenly distributed through the body at the same concentration as in plasma
What does it mean to have a very high Vd?
It suggests that the drug is being sequestered in tissue and distributes preferable to tissues.
What does it mean to have a very low Vd?
It suggests that the drug is not being distributed to all of the tissues.
Total body clearance
The volume of distribution of drug in the body cleared of the body per unit time
sum of the clearance by the kidneys, liver, and everywhere else
As clearance increases, t1/2 ____ (increase/decrease)
Decreases
As Vd increases, t1/2 ______ (increase/decrease)
Increases
Plasma concentration at steady state (Cp)
Concentration at which the amount of drug going in is equal to the amount going out.
After how many half-lives of repeated dosing or CRI will the plasma concentration be 97% of the eventual steady state concentration?
5 half-lives
T/F: The time to achieve steady state levels depends on the dose given.
F: the time to achieve the steady is INDEPENDENT of dose
The higher the dose, the ______ (higher/lower) the Cp
Higher
Watch for units in your calculations!!!!!
Don’t make stupid mistakes….
