Multiple Dosing Flashcards
When V is < 42 L it means that
the drug is distributed in vasculature and to some extent in
interstitial or extracellular fluid space (ECF). It is not extensively distributed into the peripheral tissues.
how much
FD
how often
tau (dosing interval)
we give second and subsequent doses at
constant time intervals
as successive doses are given, if next dose(s) is given before drug is completely eliminated, drug will begin to
accumulate in the body
Css
plasma concentration at steady-state
loading C
FD/V
accumulation ratio formula
1/1-e^-k tau
Css,max formula
Css,min formula
AR definition
relates the initial concentration to Css; indicates extent to which drug accumulates under the dosing regimen
Decay
e^-kt’
Formula at any time (t’) during the steady-state
Rate in formula
FD/tau
Rate out
Cl * Css,avg
At plateau
Cl * Css,avg = FD/tau
Css, avg formula
Ass, avg
average amount of drug in the body over the dosing interval
accumulation ratio
amount after a single dose to amount after “n” doses
AR formula
C1, max * AR
Css, max
C1, min * AR
Css, min
AR is only determined by
tau
t1/2 is only determined by
Cl & V
Tau is irreversibly proportional to
AR
DL formula
Which parameters are altered when tau is increased?
dose is given less frequently
decreases AR, Css avg, Css max, Css min
Does changing tau affect the time to reach steady state?
Changing tau does not affect the tss, since tss is based on
half-life. It does however affect the steady state concentrations.