Pharmacokinetics Flashcards
After 5 half lives _______% of the drug is gone.
After 5 half lives 97% of the drug is gone.
_________________
Unlikey to have any more effect
Most drugs in veterinary medicine follow _________ kinetics
Most drugs in veterinary medicine follow First Order kinetics
Half-life (T1/2) equation
t1/2 = 0.693 x Vd / ClB
When saturation occurs, ClB (increases/decreases) and t1/2 (increases/decreases) leading to drug accumulation and potential development of side effects.
When saturation occurs, ClB (increases/decreases) and t1/2 (increases/decreases) leading to drug accumulation and potential development of side effects.
T/F: Half life is dose dependent
False, it is proportional
Dosage
“Recipe” for how much to give (mg/kg)
Bioavailability % (F%) equation
F% = AUC (extravascular) / AUC (IV) x 100%
F% is equal to ________ for IV administration
F% is equal to 100 for IV administration
One Compartment Model
Consider the body as consisting of a single, homogeneous compartment. Volume would equal the volume of distribution. Model may be closed or open taking in account for clearance.
Primary compartment method by which pharmacokinetic parameters are now determined in veterinary medicine
Stochastic model
(Non-Compartmental)
Zero Order Kinetics
Amount of drug is eliminated per unit time is fixed
Peak
Highest concentration of each dose
Dose
The amount of a drug given to an individual (mg)
Time to achieve steady state levels is (dependent/independent) of dose.
Independent
What are the components of a dosage regimen
Dosage
Route of Administration
Frequency
Duration
Plasma Concentration Steady State is reached at how many half lives
5
Extent
How much the mass (dose) of a drug changes in total
Loading Dose
Single dose administered to get the plasma concentration to a certain level, to be maintained by repeated dosing
Compartment Model
Views the patient as a number of compartments, each compartment is a collection of tissues that have similar pharmacokinetics
Pharmacokinetics
Use of mathematical modelsto quantitate the time course of drug disposition in man and animals
Allometric Scaling
Uses pharmacokinetic data in multiple species to try to predict the behavior of a drug in a species for which this information is unknown
What type of pharmacokinetic model is used for drugs that follow first order kinetics?
Non-Linear Model
Clearance
Volume cleared of the drug per unit time (mL/min/kg)
What happens to plasma concentration and half life if a dose is doubled?
Plasma concentration will increase
Half life will remain the same
Population Pharmacokinetics
System estimates pharmacokinetics by looking at populations. Mathematical techniques allow studies of large numbers of animals with less individual sampling. Can allow for development of parameters for a drug that would apply to all breeds/ages/genders/etc.
Elimination roughly equals
Metabolism + Excretion
As Vd increases, t1/2 (increases/decreases)
Increases
Multi-Compartment Model
Consists of multiple compartments. Math gets incredibly complex
Vd Equation
Vd = Dose / Cp
Bioavailability (F)
Fraction of the dose given which finds its way into systemic circulation
Intermittent Dosing Cpss Equation
DOSE x F = Cpss x CLB
Interval
Two Compartment Model
Considers the body as consisting of two compartments; a central compartment into which the drug is added and from which it is clear and a second compartment to which the drug distributes. Graphical representation shows a distribution and elimination phase.
DoseCRI Equation
= Cpss x CLB
As Clearance increases, t1/2 (increases/decreases)
Decreases
Trough
Lowest concentration of each dose
Describe the pattern of Plasma Concentration of a drug in relation to Plasma Elimination of a drug
Plasma concentration will follow the same pattern as plasma elimination, only upside down
________________________
1 half life - 50% of final Cpss
5 half lives - Cpss will be 97% of eventual steady state
Apparent Volume of Distribution (Vd)
Theoretical volume a drug would occupy if it was evenly distriuted through the body at the same concentration as in plasma
First Order Kinetics
Proportion of drug eliminated per unit time is fixed
Elimination Rate Constant
Fraction/ Proportion of the drug that would be eliminated per unit time
Volume of Distribution (Vd)
Volume of drug would occupy if it was evenly distributed at the same concentration as in plasma (L/kg)
Very high Vd ( > L/kg ) suggests that a drug is
Very high Vd ( > L/kg ) suggests that a drug is distributing preferentially to tissue and may even be sequestered somewhere
Total Body Clearance (CLB)
Volume of distribution of drug in body cleared of teh drug per unit time (mL/min/kg) and this is the sum of clearance by the kidneys, liver and everywhere else.
____________________
Takes into account both metabolism and excretion
Bioavailability (F) equation
F = AUC ( extravascular ) / AUC (IV)
Very low Vd suggests that a drug is
Very low Vd suggests that a drug is not being distributed to all of the tissues
After 2 half lives _______% of the drug is gone.
After 2 half lives 75% of the drug is gone.
Bioequivalence
Different formulations of the same drug have the same drug bioequivalence when they are absorbed to a similar extent and similar rate
Stochastic Model
(Non-Compartmental)
Involve using analysis of large numbers of actual animal data (time-plasma curves).
Elimination Half Life
Time required for the drug concentration to decrease by one half or 50%
Rate
How fast the mass (dose) of a drug changes per unit time (mg/min)
Bioavilability is a measure of
Bioavilability is a measure of drug exposure
What measurements are important to compare in bioequivalence
AUC
Cmax
Tmax
Mean Resistance Time (MRT)
Used in the non compartment model, describes the length of drug persistence in the body
Plasma Concentration at Steady State Cpss
Concentration at which the amount of drug going in is equal to the amount going out
After 3.3 half lives _______% of the drug is gone.
After 3.3 half lives ~90% of the drug is gone.
