c- If you know the and the amount of drug at any time, you can determine the time required for the amount of the drug to decrease to a certain value.
You can substitute for the
values of A1, A2 and k in any of
these equation to calculate the time(t).
A1
A2
t = ?
After administration of an iv dose of theophylline the amount of theophylline remaining in the body after 3 hours was 250 mg. What is the time required for the amount of the drug in the body to decrease to 100 mg, if the elimination rate constant of theophylline in this patient is 0.183 hr -1 ?
A2 = A1 e-k(t2 -t1)hr
100mg = 250mg e-0.183hr-1(t2 -t1)hr
ln(100mg/250mg) = -0.138hr-1(t2 -t1)hr
-0.916 = -0.138hr-1(t2 -t1)hr
t2 -t1 = 5hr
You can substitute for the
values of A1 A2, and k in any of
these equations to calculate the time (t).
A1 = 250 mg
A2 = 100mg
t = ?
k = 0.183 hr -1
