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Pharmacology Exam 1: Pharmacokinetics
pharmacokinetics
81
Anatomy
Graduate
01/22/2011

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Term
kinetic=
Definition
motion
Term
pharma=
Definition
drug
Term
describe the one-compartment model of the body:
Definition
- one input
- one output
- one volume in which the drug is dissolved
Term
three forms of kinetics:
Definition
- zero order
- first order
- mixed order
Term
First order kinetic formula:
Definition
rate= [D]k

these are the most common
Term
With a first order reaction, if the y-axis is in linear units, the process will be ____.
Definition
exponential
Term
With first order reactions, if the y-axis is in log form, the process will be ___.
Definition
linear
Term
define half life:
Definition
- duration required for half of the process to be complete
- half of the remaining drug to be absorbed
- half of the remaining drug to be eliminated
Term
With first order kinetics, the half life is a function of the constant. give this equation.
Definition
t1/2= 0.693/k
Term
ka:
Definition
the constant governing absorption
Term
ke:
Definition
constant governing elimination
Term
what does it mean if ke=0.10/hour?
Definition
this means that 10% of the REMAINING drug is eliminated per hour
Term
So if the ke of a drug is 0.10, what is its half life?
Definition
t1/2=0.693/.10

t1/2= 6.93 hours
Term
For first order kinetics, the rate of elimination changes as a function of the ___ ___, and because the ___ ___ is always ____, the rate is always getting ____.
Definition
- drug concentration
- drug concentration
- declining
- slower
Term
___ changes with drug concentration, but __ ___ and ___ do not change.
Definition
Rate changes
half life and K do not
Term
For purposes of medicine, we will say that a first order process is complete when ____ ____ ____ have elapsed.
Definition
4-5 half lives
Term
for zero order kinetics rate is equal to?
Definition
rate=k
Term
for zero order processes the ___ of the ___ is irrelevant.
Definition
concentration of the drug
Term
Recognize that a rate constant of, e.g., .025%/hr is different for ethanol than for any other drug.
Definition
Term
zero order processes are rare for ____, but more common for ____.
Definition
elmination
input
Term
examples of zero order inputs:
Definition
- infusions
- medication schedules (take 1 pill every 8 hours)
Term
give an example of zero order elimination:
Definition
alcohol
Term
With 0 order processes, if the y-axis is linear units, the process is ___.
Definition
linear
Term
With zero order processes, if the y-axis is in log units, the process is ____.
Definition
hyperbolic
Term
what causes zero order kinetics?
Definition
- metabolizing enzymes get saturated
- transporter gets saturated
Term
With zero order kinetics, what happens near the end of the process when the enzymes aren't saturated anymore?
Definition
- first order kinetics prevail
- with alcohol, this occurs at such low blood concentration, that no physiological effect is detectable
Term
mixed order kinetic synonyms:
Definition
mixed-order kinetics
dose-dependent kinetics
Michaelis-Menton kinetics
Term
whats the issue with drugs that have mixed order kinetics and why?
Definition
- potential for serious drug toxicity b/c drugs that are eliminated by zero order can reach high plasma concentrations rapdily, but rate does not increase with increased drug concentration
Term
define volume of distribution:
Definition
Vd=dose/(plasma[D])

Vd should be between 40 and 60 Liters
Term
If you calculate Vd at time 0, you are calculating the ___ volume of distribution, which is the volume of fluid that the drug would occupy if what happened?
Definition
- apparent volume of distribution is calculated at time 0
- if the drug were distributed instantly throughout that volume
Term
From general principles, we know that drugs do not distribute instantly throughout their volume.
it takes times for the drug to come to equilibrium with different compartments (a case where our one-compartment model suffers)
Definition
Term
look at slides 32 and 33 of pharmocokinetics lecture
Definition
Term
if you see Vd in L/kg weight, its probably for ___.
Definition
pediatrics
Term
Vd is used to determine ___ ___.
Definition
loading dose
Term
how many liters of fluid are in the plasma, how many in extracellular space, how much total body fluid?
Definition
4 Liters in plasma
12 Liters in extrecellular compartment
40 Liters total body water
Term
Fat soluble drugs will have a ___ plasma concentration and a ____ volume of distribution.
Definition
low plasma concentration
high volume of distribution
Term
why would a volume of distribution be very small?
Definition
- all the drug is trapped in the plasma bound to proteins, so the plasma level is artificially high, making the Vd very small
Term
Volume of distribution is an ___ ___ number.
Definition
apparent mythical
Term
Vd is useful for:
Definition
calculating loading doses and multiple doses
Term
The larger the Vd, the ___ the rate of elimination, why?
Definition
slower
- because if drug is in a large volume, very little is availabe to interact with elimination mechanism
Term
define clearance:
Definition
- apparent volume of fluid from which drug is totally removed per unit time

Cl= (Vd)(Ke)
Term
what is clearance useful for?
Definition
- useful for calculating plateau concentration of drug
- useful for understanding what happens when ke changes (renal failure)
Term
To figure out single dose kinetics, x-axis is in units of ___ ___ ___, while the y-axis is in ___ of ___ ___.
Definition
- elimination half lives
- log of drug concentrations
Term
with a single dose curve, the time to get from the dose to the the peak is constant despite the dose.
Definition
Term
with single dose kinetics, peak concentration is a direct function of the ___. So if the dose if 4 times higher, the peak will be __ times higher.
Definition
peak
4
Term
With single-dose kinetics, for every doubling of the dose, the duration of effect is only extended by __ ___ ___ ___.
Definition
one elimination half life
Term
For most drugs, if you want to significantly extend the duration of action, you must give more than one dose.
giving a single, bigger dose usually exposes the patient to toxicity before the duration of action is increased significantly.
Definition
Term
With single-dose kinetics, the time to peak absorption is inversely related to ___.
Definition
Ka

- so as Ka becomes smaller (less drug absorbed per unit time), the time to peak shifts to the right (takes longer)
Term
Depot preparations produce low, sustained ___, nearly __ ___ of absorption.
Definition
-rates
- zero order
Term
a slower rate of absorption, or smaller ka, will change the peak how?
Definition
decrease the peak and shift it right
Term
why is the slowing the rate of absorption beneficial sometimes?
Definition
- helps to get rid of peaks and valleys
- you can help control rate of absorption by administering via different routes
Term
change in rate of elimination is inversely related to to changes in ___.
Definition
ke
Term
So as Ke gets smaller, the half life of elimination gets ____.
Definition
bigger
Term
As Ke gets smaller, elimination half life gets ___, time to peak shifts to the ___ and the peak gets ___, and the duration is ___.
Definition
- longer
- right
- higher
- longer
Term
In single dose drugs, if Ke is smaller it really doesn't matter b/c the increased peak is no big deal, this is just important with multiple doses.
Definition
Term
___ ___ may be a critical factor in deciding amount for subsequent doses.
Definition
varied elimination
Term
Repeated doses are referred to as ___ doses when the dose and dosing intervel are constant. These types of drugs are ___ order input and ___ order elimination.
Definition
- maintenance
- zero order input
- first order elimination
Term
With maintenance doses, drug accumulates in the system until a ___, or stable concentration is reached.
Definition
plateau
Term
what type of elimination is essential for a plateau to be reached?
Definition
first order elimination
Term
With maintenance dosing, at the start of the first dose, no drug is being eliminated.
Definition
Term
With developing a maintenance dose, if the second dose is given within 4-5 elmination half lives of the first dose, peak concentration attained will be ___ than the first dose.
Definition
higher
Term
how long does it take to reach a stable plateau?
Definition
4-5 half lives
Term
Consider why the plateau occurs. Elimination rate= [D]k. After the second dose, peak concentration is higher than after the first dose, thus rate of drug ___ is higher after the second dose. This process repeats after every dose, until the amount of drug ___ ___ equal the amount of drug ___. Then a plateau has been reached.
Definition
- elimination
- amount of drug coming in= amount of drug being eliminated
Term
Once the plateau has been achieved, if medication is stopped, how long does it take for the drug to be completely eliminated?
Definition
4-5 elimination half lives
Term
How long it takes to reach plateau is governed soley by the ___ ___ ___.
Definition
elmination half life
Term
at constant dose, with constant dosing interval, and drug eliminated by first-order kinetics:
4-5 elimination half-lives to reach plateau
Definition
Term
the height of the plateau is a direct function of the ___ ___.
Definition
maintenance dose

so if you double the dose consistently, you double the plateau
Term
greater dosing intervals produces greater __ and ___ around the plateau.
Definition
peaks and valleys
Term
the more rapid the absorption, the greater the ____ around the plateau
Definition
Term
as Ke, or rate of elimination, gets smaller and slower, the elimination halfe life is getting ___, and the plateau ___.
Definition
longer
increases
Term
we worry about slower than expected elimination not really faster than normal elimination.
Definition
Term
When possible, start with maintenance dose
safety: if toxic effects occur at concentrations below the intended plateau, the drug can be discontinued or the maintenance dose can be adjusted
Definition
Term
use maintenace dose to start with not loading dose
Definition
Term
Life threatening problems require rapid attainment of the plateau. Use a loading dose.
safety: even if you must use a loading dose, avoid going directly to plateau if possible -- e.g., multiple loading doses.
The next slide illustrates two large doses given close together as loading doses
Definition
Term
even when giving a loading dose, the ___ ___ ultimately determins plateau.
Definition
maintenance dose
Term
If you know the desired plasma concentration of the drug, how do you calculate the dose?
Definition
- desired plasma concentration
- approximate volume of distribution
- ([D] in plasma)= dose/Vd
Term
tips for calculating loading dose:
Definition
Usually it is best to aim for the low end of the therapeutic window
When switching to a maintenance dose, monitor the patient closely. For example, if ke is smaller than anticipated, the ultimate plateau may rise higher than anticipated.
Term
necessary parameters to consider when calculating the loading dose:
Definition
1. Bioavailability= F, the fraction of each dose that gets into the plasma
2. Volume of Distribution= Vd, the apparent volume the drug dissolves in
3. Cl= (Vd)(Ke)
4. the maintenance dose (drug per unit time)

Think BVCM: Be Very Cool Mom.
Term
plateau concentration is also known as concentration at steady state (CSS), give equation for this:
Definition
Css= ((F)(maintenance dose))/Cl

THIS PREDICTS THE AVERAGE CONCENTRATION, IGNORING PEAKS AND VALLEYS.
Term
If there is not information about bioavailability, assume it is __.
Definition
1
Term
units of maintenace dose is quantity/per unit time. So if told someone is taking 50mg of drug X every 12 hours, what is the maintenance dose?
Definition
50/12= 4.17 mg/hour is the maintenance dose
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