Vancomycin 1C Infusion Time to SS A 65-year-old female patient with a past medic
ID: 183674 • Letter: V
Question
Vancomycin 1C Infusion Time to SS A 65-year-old female patient with a past medical history of diabetes mellitus and an allergy to penicillin develops an infected abscess positive for MRSA on the third day of her hospital stay. She is started on an IV infusion of vancomycin at a dose of 1000 mg every 12 hours. Vancomycin is eliminated by first-order kinetics and has a half life of 6 hours. The volume of distribution of vancomycin is 0.5 L/kg. Assuming no loading dose is given, how long will it take for the drug to reach 94% of its plasma steady state concentration? A. 6 hours B. 12 hours C. 8 hours D.24 hours E. 30 hoursExplanation / Answer
Everyone knows how long it takes to reach a steady state if a drug is given at a regular interval that is four to five half-lives. It is because, in a single dose, serum concentrations decline to the following levels:
So, by 4 × t1/2 to 5 × t1/2, the serum levels are reduced by almost 94% to 97% of the peak level. In other words, the entire dose you gave is almost gone from the body by 4 × t1/2 to 5 × t1/2.
Hence according to the question half life of the vancomycin is 6 hours(t1/2). Thus inorder to reach the 94% plasma steady state concentration it needs about four half lives as shown below:
50%....................1st half-life
25%....................2nd half-life
12.5%.................3rd half-life
6.25%.................4th half-life
Total= 93.75 %
hence inorder to determine the number of hours required to reach 94% plasma steady state conc. we can simply incorporate values below:
No. of half-lives required x Half life of Vancomycin
i.e, 4 x 6 = 24 hours
24 hours is the answer.
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