c- If the patient is at steady state:

Two plasma samples are obtained. One sample is obtained just before drug administration and the other is obtained after 0.5 - 1 hr of drug administration.

At steady state Cpmax ss and Cpmin ss are not changing from one dosing interval to the other.

The conc in the sample obtained before drug administration should be equal to the drug conc at the end of the following dosing interval.

(This is true only at steady state)

i- The half life can be determined graphically

- The elimination rate constant can be determined from the slope of the line.

- The elimination rate constant can also be determined mathematically.

Cp t2 = Cp t1 e-kt
Cpmax ss
Cpmin ss
Cpmax ss
slope = -k/2.303
t 1/2
Cpmax ss =

K0( 1 - e-kt' )

k Vd( 1 - e-kτ )

ii- The maximum plasma conc can be determined mathematically, or graphically by back extrapolation of the line that goes through the samples.

iii-The Vd can be determined from the expression that describes Cpmax ss because all the other parameters are known.

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