PHARM: Clinical Pharmacokinetics Flashcards Preview

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Flashcards in PHARM: Clinical Pharmacokinetics Deck (40)
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1
Q

True or False: IV administration is the fastest route of drug absorption.

A

False- when administered via IV, there is no drug absorption

2
Q

How can the rate of elimination of a drug be calculated in a one-compartment model?

A

Rate of Elimination (Vel)= Inherent rate of Elimination (Kel) * [Drug] in the body ([A]c)

3
Q

What does it mean if a drug follows a 1st order process of elimination?

A

The drug elimination is proportional to the drug concentration in the body

4
Q

True or False: Kel is a constant for a particular drug.

A

False: Kel can be different from individual to individual and can be different in the same individual at different times

5
Q

How can Kel be determined from a Semi-log plot of [drug] vs. time?

A

Kel is the slope of the line

6
Q

What is the half life of a drug?

A

The time it takes for half of the drug to be eliminated from the body

7
Q

What is the relationship between half-life and the elimination rate constant for first order drugs?

A

Kel=0.693/T(1/2)

8
Q

What sorts of drugs are zero order drugs?

A

Drugs whose metabolism or elimination is mediated by proteins, and thus, is saturable

9
Q

What is the appearance of a regular and semi-log plot of a zero order drug?

A

Regular plots show a linear decrease, and semi-log plots are concave downward until the rxn is no longer is zero order

10
Q

How can the rate at which a drug is absorbed be calculated for a drug administered extravascularly in a one compartment model?

A

Rate of absorption (Vabs)= absorptive rate constant for the drug (Kabs) * concentration of the drug at the absorptive site ([A]a)

11
Q

How can a drug following a one-compartment model and in a first order process be identified by looking at a semi-log plot?

A

The semi-log plots for these drugs will simply be a straight line

12
Q

Following administration into a two compartment model via intravascular bolus and accumulation in the central compartment what two process can happen to the drug?

A

Elimination or Distribution to peripheral compartment

13
Q

How can distribution from the central to peripheral compartment be calculated?

A

Vcp= Kcp (rate constant for drug describing ability to distribute from central to peripheral compartments) * [A]c (conc. of drug in central compartment)

14
Q

How can distribution from the peripheral to central compartment be calculated?

A

Vpc= Kpc * [A]p

15
Q

On a regular plot of a two compartment model drug what is alpha and what is beta? What is happening to the drug during those periods?

A

Alpha is the distribution phase that consists of the rapid decrease in [drug] from initial concentration. Beta is the disposition phase, which consists of distribution, redistribution, and elimination of drug

16
Q

How can beta be calculated for a two-compartment model drug?

A

Beta= 0.693/T(1/2)beta, where T(1/2)beta can be determined by using the linear portion of a semi log plot (indicating the cessation of distribution/redistribution)

17
Q

What are the three phases of a semi-log plot of a drug administered extravascularly into a 2 compartment system?

A

Absorption, Distribution, Disposition

18
Q

What is the utility of apparent volumes of distribution?

A

Gives an idea on where a drug goes once it enters the body

19
Q

How can apparent volumes of distribution be calculated?

A

Give a patient a drug of a known amount, take blood levels (concentration) over time and then extrapolate the concentration to time point 0 prior to any elimination. Dividing the amount of drug by the concentration at time 0 will give the apparent volume of distribution

20
Q

A drug is given to a patient and has a calculated apparent volume of distribution equal to 5.5 L. Where is the drug primarily located?

A

Within the vasculature

21
Q

A drug is given to a patient and has a calculated apparent volume of distribution equal to 14.6 L. Where is the drug primarily located?

A

In the vasculature and ECF

22
Q

A drug is given to a patient and has a calculated apparent volume of distribution equal to 105.5 L. Where is the drug primarily located?

A

Some tissue compartment of the body

23
Q

What is bioavailability?

A

The fraction of drug that reaches systemic circulation- essentially a measure of absorption of a drug and how effectively it is absorbed

24
Q

How can bioavailability be determined?

A

First administer a drug via IV, measure drug concentration over time and measure the area under the curve of a regular plot. Next administer the drug via extravascular route and obtain the area under the curve. Bioavailability (F)= AUCx/AUCiv

25
Q

What is the interpretation of “When administered sublingually, THC has an F of 1?”

A

All of the THC that would have entered into systemic circulation directly via IV is the same amount that would get into circulation via sublingual administration

26
Q

What is clearance?

A

The theoretical volume of fluid from which a drug is completely removed in a given period of time

27
Q

What two equations can be used to determine total clearance?

A

Clt=Kel * Vd; =Xo/AUC

28
Q

What is the extraction ratio and how is it calculated?

A

E is the efficiency at which an organ extracts a drug and is =(Cin - Cout)/(Cin)

29
Q

How could one determine clearance of a drug from the liver?

A

Clh= Q (rate of blood flow) * E

30
Q

What are the three processes that contribute to renal clearance of a drug?

A

Glomerular filtration, Active secretion, passive reabsorption

31
Q

How is renal clearance of a drug calculated?

A

Clr=Clglomfilt + Cl (actsec) - Cl(tubReab)

32
Q

What is the minimum effective concentration?

A

The concentration of a drug needed to produce its pharmacological effect

33
Q

What is the steady state concentration?

A

The concentration at which a drug administered continuously has a dose rate = rate of elimination such that the blood concentration of a drug remains stable

34
Q

How can steady state concentration be calculated

A

Css=dose rate/ Ct or dose rate/ Kel * Vd

35
Q

When administering a drug via IV infusion how long does it take for a drug to reach half of its steady state concentration?

A

One half life

36
Q

When administering a drug via IV infusion how long does it take for a drug to reach its steady state concentration?

A

4-5 Half lives

37
Q

How does increasing the frequency of a smaller dose of a drug effect its pharmacokinetics?

A

There is smaller fluctuations in the concentration level

38
Q

What is a loading dose? When is it needed? How can it be calculated?

A

A loading dose is a higher first dose given when the therapeutic window must be reached quickly. Loading dose (X*)=Css *Vd

39
Q

How would a graph of multiple IV administrations differ from a graph of multiple extravascular administrations?

A

The spikes on the fluctuations would be more rounded due to absorption slowing down the process

40
Q

How can the steady state concentration of a drug administered multiple times be calculated?

A

Css= (F*dose rate)/Clt