Example: Theophylline is a drug used in the treatment of bronchial asthma. A dose of 600 mg was administered as a constant rate iv infusion over 2 hours. What is the plasma theophylline conc at the end of drug administration and 4 hours after the end of drug administration ? (Theophylline Vd is 30 liters and k is 0.1155 hr-1 )
Dose = 600 mg
t' = 2 hr
Ko = Dose/t' = 300 mg/hr
k = 0.1155 hr-1
Vd = 30 L
At the end of the infusion t = t'
So the equation is reduced to:
Cp =
K0
k Vd
( 1 - e-kt' )
Cp =
300 mg/hr
0.1155hr -1 30L
( 1 - e-0.1155hr -1 2hr ) = 17.9 mg/L
Plasma conc 4 hr after the end of infusion:
You can substitute in the full equation or;
Cp 4hr = ( 17.9 e-0.1155hr -1 4hr ) = 11.3 mg/L
