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43 Cards in this Set

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In multiple dosage regimens it is assumed that a drug is eliminated by what process?
It is eliminated by a first-order process and that early doses have no effect on the kinetics of later doses. The kinetics of later doses are only superimposed on earlier ones.
Based on the principal of superimposition, the concentration-time curve in a multiple dosing case can be predicted from what?
It can be predicted from the concentration-time data of a single-dose administration.
If a constant dose is given at constant time periods, the plasma concentrations after each dose consists of what? So, for each time point what is the predicted plasma concentration?
If a constant dose is given at constant time periods, the plasma conc. after each dose consist of the same data obtained after the single dose. For each time point, then, the predicted plasma concentration is the sum of the residual concentration resulting from each previous dose. (This holds true even if the dosing interval is not fixed)
List 5 situations in which superposition would not be valid.
1. Drug does not follow linear kinetics

2. A drug's carrier system gets saturated (for instance, drug is eliminated by a saturable enzymatic process and so follows michaelis-menton kinetics; recall Vmax and Km)

3. There is enzyme induction

4. There is enzyme inhibition

5. The patients disease condition changes significantly between doses
What is the point of multiple dosing?
It is intended to keep plasma drug levels within the therapeutic window.
In multiple dosing what may be adjusted to to keep plasma drug levels within the therapeutic window?
The dose and time between doses.
In multiple dosing when will accumulation fail to occur?
Accumulation will not occur if a second dose is given at a longer interval than that required for the elimination of the previous dose.
During accumulation what should eventually be achieved?
Steady state should eventually be achieved. This means Cmax and Cmin should remain the same from dose to dose.
If there is no accumulation, steady state Cmax for a later dose is the same as what?
Cmax for the first dose.
For drug safety Cmax should always be what?
Should always be less than the minimum toxic dose.
What does accumulation depend on?
Accumulation does not depend on the dose. It depends on the dosing interval and the elimination rate constant.
The time reqd to attain steady state is dependent on the ? but is independent of ? or ?.
The time reqd to attain steady state is dependent on the elimination half-life but is independent of dose or interval between doses.
In drug accumulation for iv infusion administration ka is ?.
ka is rapid >>> k
The time need to reach:

1. 90% steady state conc?

2. 99% steady state conc?
1. 3.3 t1/2

2. 6.6 t1/2
In drug accumulation the number of doses needed to reach steady-state is dependent on what?
t1/2 and time interval between doses.
When speaking of drug accumulation what does f represent?
f is the fraction of the dose remaining in the body.
What does f depend upon?
k and time interval between doses.
If the time interval between doses is small then f is ?.
Then f is large.
F = fraction of dose absorbed. For an IV dose what does F equal.
F = 1
In drug accumulation the difference between the max and min amts of drug in the body is equal to what?
The difference between the max and min amts of drug in the body is equal to the administered dose. (original dose)
In a plasma level eqn at ss e^-nkT is equal to what?
It approaches zero.
The more ? a missed dose is, the greater effect it will have on the ?.
The more recent a missed dose is, the greater effect it will have on the current plasma concentration.
Missed doses greater than ? ? ? later should be omitted because of their minimal impact.
Missed doses greater than 5 half-lives later should be omitted because of their minimal impact.
For repeat IV infusions, intermittent short IV infusions prevent what? What does this mean?
Intermittent short IV infusions prevent transient extreme high plasma levels of a drug and so are better tolerated even though steady-state may not be attained.
In repeat IV infusions what does D represent? R? tinf?
D is the size of the infusion. R is the infusion rate. tinf is the duration of the infusion.
What is the point of a loading dose?
It is used to achieve the desired plasma concentration (Cav) promptly, circumventing the delay that the process of absorption introduces.
When determining a loading dose; when the dosage interval is equal to the half-life, the dose ratio has a value of what?
2
In multi-dose regimens an estimation of what is difficult? Why?
An estimation of ka is difficult with multi-dose regimens because of superposition of doses.
The determination of bioavailability is possible when?
At steady state.
When should the first sample be taken?
Just before admin. of the 2nd dose, thereafter, doses should be taken regularly after the administration of each dose.
Multi-dose regimen bioavailability studies can reveal what?
They can reveal changes that would not be obvious in a single dose study. For example, the existence of non-linear kinetics, drug-induced malabsorption syndrome, etc,.
What can be designed to ascertain bioequivalence? Explain.
A multiple dose study. Equal doses of test and a reference product may each be administered repeatedly in turn (two-way cross-over) to steady state, separated by a time period required to completely eliminate the drug from the body. The AUC and Cmax of the test product should be w/n 80-125% of the corresponding values for the reference product using a 90% confidence interval.
The area under a plasma drug concentration vs time curve is a measure of what?
It is a measure of the amount of drug exposure.
What can a high fecal drug conc. indicate?
It can be an indication of biliary secretion after systemic absorption.
Urine concentration of a drug is NOT what?
It is not a DIRECT indication of the systemic conc. of the drug.
Saliva drug conc.s assayed after equilibrium with plasma drug conc.s is an ? measure of ?.
Saliva drug conc.s assayed after equilibrium with plasma drug conc.s is an indirect measure or drug levels in the body.
What may be used to explain drug interactions.
A pharmacokinetic model.
In a 2-compt. model, at steady state, what is equal?
In a 2-compt. model, at steady state, the central compt. is equal to the conc. of the drug in the peripheral compt.
In a 2-compt model at steady state what is equilibrated?
The drug between the central and peripheral compt.s
In the 2-compt model the rate of drug diffusion into the central compt. is equal to what?
It is equal to the rate of drug diffusion from the central compt.
In a 2-compt model, upon equilibration, the rate of drug entry into the peripheral compt equals what?
The rate of drug entry into the peripheral compt equals the rate of exit.
In a 2-compt model the volume of the central compt is greater than what?
In a 2-compt model the volume of the central compt is greater than the volume of distribution determined by area.
In a 2-compt model the vol. of distribution determined by area is dependent on the value of the what?
It is dependent upon the value of the rate constant of the beta phase.