# final-review with answers - The half-life of a drug is 4...

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The half-life of a drug is 4 hours and its volume of distribution in a patient is 45 L. (A) What infusion rate is required to maintain a concentration of 20 mg/L in this patient? Q = C ss * k * V and k = 0.693/t 1/2 = 0.693/4 = 0.173 hr -1 . Therefore Q = 20 mg/L * 0.173 hr -1 * 45 L = 155.9 mg/hr (B) What is the clearance of this drug? Cl = kV = 0.173 hr -1 * 45 L = 7.8 L/hr (C) What loading dose would you have to give this patient to bring him to 20 mg/L? Loading dose = 20 mg/L * 45 L = 900 mg (D) If you stopped infusing drug into this patient and he had a drug concentration of 20 mg/L at that time, how much time would elapse until his body concentration was 3.5 mg/L? t 0 -kt t 0 -1

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In accordance with the plateau principle, if the half-life of a drug is 4 hours, how many hours will it take to reach 75% of the steady state concentration. f = 1 – e -kt , f = 0.75, k = 0.693/4 = 0.173, and you solve for t So 0.75 = 1 – e- 0.173t , so 0.25 = e -0.173t . Now take ln of both sides, -1.39 = -0.173t, so t = 8 hrs
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## This note was uploaded on 02/08/2010 for the course BIO 51310 taught by Professor Sisson during the Spring '08 term at University of Texas.

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final-review with answers - The half-life of a drug is 4...

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