Quantitative pharmacokinetics part 1 Flashcards
What is volume distribution?
The volume of plasma that would be required to contain the drug dose at the concentration measured in plasma.
Volume distribution can be greater than total volume of a human due to tissue binding. TRUE OR FALSE?
TRUE
From desired C and knowing VD we can estimate the required dose. TRUE OR FALSE?
TRUE
What is clearance?
volume of plasma cleared of drug per unit time
What is clearance used to estimate?
Used to estimate rate of elimination of the drug
What is the equation for rate of elimination?
Rate of elimination = Cl x C
What is the equation for calculating dose?
Dose = Cl x AUC∞
By measuring AUC∞ we can calculate Cl. TRUE OR FALSE?
TRUE
How can clearance be measured?
By measuring the area under the curve
What is half life?
The time required for elimination of half of the absorbed drug
What is a first order process?
The Rate is proportional to one variable/ rate is dependent on drug
What is a zero order process?
It depends on zero variables/ Rate is constant and doesn’t change with [Drug]
What is extraction ratio?
Is the fraction of drug entering a tissue that is eliminated
What does C0 mean?
concentration of drug in plasma at t=0 (immediately after administration)
What is the equation fro exponential decay?
C=C0e-kt
What does K mean in the exponential decay equation?
elimination rate constant, fraction of drug eliminated per minute
What is the equation for calculating half life?
kt½ = ln 2
If know k, can calculate t½. TRUE OR FALSE?
TRUE
If you know Vd you can calculate the dose for any give n concentration. TRUE OR FALSE? and provide equation for this
TRUE
VD = Dose/C0
What is Intravenous Infusion?
Drug delivered over minutes-hours
What are the reasons/benefits for having Iv infusion?
- allows precise and controlled exposure
– adjust concentration
– stop if required
– short infusion sometimes used to reduce Cmax and adverse events following rapid bolus injection
What is the equation that helps to describe the relationship between clearance and elimination rate constant?
k = Cl/VD
If clearance is big the half life will be small and vice versa. TRUE OR FALSE?
TRUE
The half life is controlled by how much volume of the drug appears to be dissolved in and by what volume of plasma is cleared per unit time . TRUE OR FALSE?
TRUE
What occurs when drug concentration increases to a plateau value Css? and what is the equation that describes this?
Rate of elimination is equal to rate of infusion
C = Css(1-e^-kt)
What does this equation describe? C = Css(1-e^-kt)
Concentration in plasma gets exponentially closer to Css as time progresses but it never reaches it
What is a loading dose useful for?
Useful to quickly reach Css
bolus iv dose
What is the equation for required rate of infusion?
Rinf = Cl x Css
What is the equation for loading dose?
Loading dose = Css * VD
How many half life’s does it take to reach 90% of plateau?
3.3 t½
Plateau concentration determined by infusion rate
and clearance
Increasing the infusion rate will increase the final Css. TRUE OR FALSE?
TRUE
Time to reach plateau depends on the elimination
constant (or t1/2). Increasing the infusion rate will NOT REDUCE the time to reach Css because Css will be increased. TRUE OR FALSE?
TRUE
What is Linear pharmacokinetics?
pharmacokinetic parameters don’t change with dose
– increasing dose increases exposure
What is Non-linear pharmacokinetics?
– Pharmacokinetic parameters change with dose of drug
– increasing dose has a disproportionate effect on exposure
Rate of increase of
drug in body = Rate of absorption - Rate of elimination . TRUE OR FALSE?
TRUE
what is the difference in terms of Cmax and Tmax in P.o compared to I.v?
reduced Cmax
increased Tmax
What is meant by “Absorption can become rate-limiting” in P.O administration?
Rate of absorption controls rate of elimination, only happens when absorption is slow and rate limiting
What is Bioavailability?
Fraction of administered drug that reaches the systemic circulation
In I.V administration all drug is not systemically available . TRUE OR FALSE?
FALSE
Non i.v. – some drug may not reach systemic circulation. TRUE OR FALSE?
TRUE
What equation can be used to calculate the amount of drug reaching systemic circulation?
F x Dose (Bioavailability * Dose)
Why is bioavailability important ?
because we want to determine the dose of drug to give a patient, so we need to know the proportion that gets absorbed
What equation is used to measure bioavailability for P.o?
Fpo = Doseiv * AUCpo/Dosepo * AUCiv
How can Bioavailability be measured?
By measuring AUC we can determine F
If the doses are equal, F is simply the ratio of the two AUC values. TRUE OR FALSE?
TRUE
What is the constant steady state Css dependent upon?
Depends on dose & frequency
What is the equation to calculate dose for P.o taking into consideration bioavailability?
Dose = t * Cl *Css, av/ F
What is a loading dose?
An initial “high” dose of drug to quickly plasma drug
concentration to the desired level
– particularly important for drugs with large VD
What is Maintenance dose?
Once desired plasma drug concentration is achieved, them maintenance dose compensates for drug elimination
