Drug concentration-time profile

The plasma conc during constant rate iv infusion can be described by :

Cp =

K0

k Vd ( 1 - e-kt )

Assumptions:

1- The drug follows one-compartment pharmacokinetic model

2- The drug is administered by a constant rate (zero-order)

3- The drug elimination follows first-order kinetics

Notice that if the infusion duration is very long (t = ∞), e -kt will be equal to zero. The resulting expression will describe the plasma conc at steady state during constant rate iv infusion.

Cp ss =

K0

k Vd

For an infusion for a duration of ( t' ) :
The plasma conc at the end of the infusion:

Cp =

K0

k Vd ( 1 - e-kt' )

Where Ko is equal to Dose/t'

t '
Drug conc at
the end of drug
administration
Drug concentration
after the end of
drug administration
t
t is the time from the start of drug administration

If a dose of 100 mg is administered over 1 hr (t'=1 hr), K0=Dose/t'= 100 mg/hr.

If a dose of 100 mg is administered over 0.5 hr (t'=0.5 hr), then Ko=Dose/t'= 200 mg/hr.

The plasma conc at any time after the end of drug administration:

Cp = [

K0

k Vd ( 1 - e-kt' )] e-k(t-t')
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