Example: The plasma theophylline concentrations after administration of a single 500 mg dose were 6, 10, 9, 6, 3.7, and 2 mg/L at 1, 3, 6, 10, 15, and 20 hr, respectively.

Calculate the elimination rate constant and total body clearance of theophylline in this patient if the observed AUC was 140 mg-hr/L and F is 100%.

Identify the linear portion of the curve that represents drug elimination.
Calculate k or the half life from the line.

t1/2

CLT =

F Dose

AUC

Graphically t1/2 = 6hr

k =

0.693

6hr =0.1155 hr-1
CLT =

(1) 500 mg

140 mg-hr/L = 3.57 L/hr

  • Page 2 of 2
  • 1
  • 2