In: Chemistry
HC is a 55 year old female on a continuous infusion of an
antibiotic. The total dose that will be given is 1500 mg over 16
hours. The volume of distribution is 51 L and the drug half life is
6.5 hours.
What is the plasma drug concentration if a blood sample is taken 17
hours after the infusion began? Note: Please provide your
answer in units of mg/L.
____
Half life of the drug is 6.5 hours.
Half life of a first order reaction is,
t1/2= 0.693/k
So, k= 0.693/t1/2
k= 0.693/ (6.5 *60*60)s
k= 2.96 * 10-5s-1
Total dose given in 16 hours is 1500 mg. So, to find the concentration of the drug after 17 hours, we have to do the following.
From the equation for first order reaction,
ln [A]t = ln[A]0 -kt
[A]0=1500 mg
t=1 hour = 3600 s
k = 2.96 * 10-5 s-1
So,
ln [A]t= ln [1500] - 2.96 * 10-5s-1 * 3600 s
ln [A]t= 7.21
[A]t= e7.21 = 1574 mg
Drug concentration after 17 hours is 1574 mg.