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10. Drug Accumulation
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Terms in this set (25)
___ ___ - time taken for the plasma concentration of a drug to fall by one half
half-life
What is the formula for the half life of a drug?
t(1/2) = 0.7 (Vd)/CL
If a kinetic process is first order, the half-life of a drug is ____
constant
What is the four half-life rule?
a drug is considered to be eliminated by the body in four half lives
50% after 1t(1/2)
25% after 2t(1/2)
12.5% after 3t(1/2)
6.25% after 4t(1/2)
What will happen if the dosing interval is shorter than 4 half-lives?
accumulation will occur
Half-life of a drug can be determined from what curve?
time-concentration curve
Half-life:
It is assumed that a drug is effective when its concentration in the body compartment is greater than what level?
minimal threshold level
Assuming first order process, the duration of drug effects will be proportional to what factors?
- half-life
- administered dose
The consideration of half-life and administered dose as the only factors cannot be applied in two scenarios?
- redistribution mechanism
- slow turnover of a physiologic substance
The termination of a specific drug is related to the redistribution mechanism. What does this mean in regards to the effect of the drug compared to the threshold?
effect will cease when drug concentration is still above threshold
A drug is dependent on the slow turnover of a specific substance. What does this mean in regards to the effect of the drug and threshold?
drug effect will be present when plasma drug concentration is negligible
If a drug following first-order kinetics is given by a constant rate, what is reached over time?
steady state
Steady state - state in which
rate ___ = rate ___
rate administration = rate elimination
Steady State:
What is the formula?
D/T = Css x CL
D = dose
T = infusion time
Css = Plasma concentration steady state
CL = total clearance
The plasma concentration of a drug in a steady state is proportional to?
Dose
The plasma concentration of a drug in a steady state is inversely proportional to?
Time of infusion
Time to reach steady state plasma concentration is it dependent on?****
Elimination half-life
Time to reach steady state plasma concentration is dependent on dosage and dosing interval. True or false?
FALSE
NOT DEPENDENT ON DOSING INTERVAL
Simple calculations indicate that mean steady-state plasma concentration is reached after __ half-lives
4
Drug Accumulation:
For drugs following a first order kinetics, how would you calculate mean plasma concentration at the steady state?
Css = (F x D)/(CL x T)
D = administered dose
F = drug bioavailability
T = dosing interval
CL = total clearance
In some cases, it may be necessary to attain an desired plasma concentration of a drug. When is this required?
1. clinical situation is an emergency
2. drug has a low therapeutic index
Loading Dose and Maintenance Dose:
What is loading dose?
dose able to quickly achieve the desired plasma concentration. this dose can be calculated
Loading Dose and Maintenance Dose:
What is the formula?
Loading Dose = (Vd x Cp)/F
Loading Dose and Maintenance Dose:
What is maintenance dose?
dose needed to mantain that plasma concentation, administered at regular time intervals
Loading Dose and Maintenance Dose:
What is the formula?
Maintenance dose/T = (CL x Css)/F
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