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PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(

Solve the following problems:

1. If the desired C ss of theophylline is 15 mg/L. The average t ½ of theophylline is about 4

hr and the Vd is about 25 liter. What is the necessary infusion rate (R)?

ANSWER

k = 0.693/4 = 0.17 hr -1

 =

R = Css . K. Vd= 15 x 0.17 x 25 = 63.75 mg/hr

– 1
2. A patient was infused for 6 hr with a drug (k = 0.01 hr ; Vd = 10 L) at a rate of 2 mg/hr.
What is the concentration of the drug in the body after cessation of the infusion?

ANSWER

 = ( − − )

= 2 / 0.01 x 10 . (1 – e – 0.01 x 6 )

= 1.164 mg/L

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