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

Frequently asked questions

 If a drug is distributed in the one-compartment model, does it mean
that there is no drug in the tissue?

 A single IV bolus injection containing 500 mg of cefamandole nafate (Mandol,
Lilly) is given to an adult female patient (63 years, 55 kg) for a septicemic infection.
(Vd = 0.1 L/kg, t½= 0.75 hr) Assuming the drug is eliminated by first-order kinetics and
may be described by a one-compartment model, calculate the following:

0
a. The Cp
b. The amount of drug in the body 4 hr after the dose is given
c. The time for the drug to decline to 0.5 mg/mL (MIC)

ANSWER

Vd = 0.1 L/kg x 55kg= 5.5L

0
a. Cp = Dose/ Vd = 500/5.5 = 90.9mg/L

t½ = 0.75 hr, k= 0.693/t½= 0.693/0.75= 0.924hr

b. Log X = Log X0 -kt/2.3 = log 500 – 0.924x 4/2.3

(Amount of drug ) X = 12.3mg

c. Log 0.5= log 90.9 -0.924 t/2.3

t= 5.62hr

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