Question

BIOCHEMISTRY 115:403/503 nation, December 18, 2017 Page 12 ID No.: Part II, Question 2. Twenty points. Please answer the question on this page, using the bick should you d it SHOW ALL, YOUR WORK. An answer with incomplete, unclear, or illegible work will be penalized. YOU OMIT THIS QUESTION, WRITE "OMIT" CLEARLY ON THIS PAGE. A medication is cleared from the blood by first order kineties with a half-time of 3.5 hours. The prescribed dose is 100 mg. This dose is distributed into the blood, whose volume is 5 L. a What is the concentration in the blood in grams per milliliter immediately upon administering the dose? sume the full dose is absorbed into the blood immediately. (b) The medicine has a beneficial effect as long as its concentration in the blood does not fall below one fith the administered dose. How often should the patient take the medicine? be

Answer 1

1) 1st order kinetics-

Half life= 3.5 hours

Dose= 100mg

Vol of blood= 5L

a) Concentration in the blood upon administering the dose=

100mg/5L= 100mg*1g*1L/ 1000mg*5L*1000ml = 2* 10⁻⁵  g/mL

b) Since the half life is 3.5 hr and it is 1st order reaction,

the rate constant is 0.693/3.5 = 0.198/hour

Since 1/5th is the margin concentration,

At/Ao =0.2

ln (1/5)= -0.198*t

Therefore, t = 8 hours.

The drug has to be administered after 8 hours.