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1. The document provides information and questions about pharmacokinetic concepts like half-life, volume of distribution, and area under the curve calculations. 2. One question asks the reader to calculate the half-life of a drug based on provided concentration levels at different time points, showing the calculation using a logarithmic graph. 3. Another question asks the reader to calculate volume of distribution, rate constant, and half-life for a drug based on plasma concentration data over time, demonstrating use of a semilog graph to determine the half-life.

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Hamza Zitouni
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142 views14 pages

Reponse

1. The document provides information and questions about pharmacokinetic concepts like half-life, volume of distribution, and area under the curve calculations. 2. One question asks the reader to calculate the half-life of a drug based on provided concentration levels at different time points, showing the calculation using a logarithmic graph. 3. Another question asks the reader to calculate volume of distribution, rate constant, and half-life for a drug based on plasma concentration data over time, demonstrating use of a semilog graph to determine the half-life.

Uploaded by

Hamza Zitouni
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Chapter-3

Learning questions
Assis. Prof. Dr. Wedad Kamal Ali
LEARNING QUESTIONS
1. A 70-kg volunteer is given an intravenous
dose of an antibiotic, and serum drug
concentrations were determined at 2 hours
and 5 hours after administration. The drug
concentrations were 1.2 and 0.3 μg/mL,
respectively.
What is the biologic half-life for this drug,
assuming first-order elimination kinetics?
Solution
The Cp decreased from 1.2 to 0.3 ug/mL in 3 hours.
t (hr) C P ( ug/mL)
2 1.2
5 0.3
Since:
log 0.3 = - 0.522
log 1.2 = 0.079
log 1.2 + log 0.3 = 3k/2.3
0.61 =3k/2.3
0.61 x 2.3 /3 = k
K = 0.46
• Alternative method: by plotting the data on a
semilog graph and t 1/2 obtained from the graph. As
shown below
10
Concentration (ug/mL)

1
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
0.6

0.3

T1/2 = 5 - 3.5 = 1.5 hr


0.1
Time (hr)
2. A 50-kg woman was given a single IV dose of an
antibacterial drug at a dose level of 6 mg/kg. Blood
samples were taken at various time intervals. The
concentration of the drug (Cp) was determined in the
plasma fraction of each blood sample and the
following data were obtained:
Time (hr) Cp (ug/mL)
0.25 8.21
0.5 7.87
1 7.23
3 5.15
6 3.09
12 1.11
18 0.4
a. What are the values for VD , k, and t 1/2 for
this drug?
Answer: To calculate VD
1. plot the data on semilog paper and then find
the value of Cp0 by extrapolation (see the
equation in the next slide)
Cp0 = 8.57 μg/mL = 8.5 mg/ L
2. Dose = 6mg/Kg X 50 = 300mg
3. VD = Dose/ Cp0
VD = 300 mg / 8.57 mg/L = 35 L
10
Plasma concentration (µg/mL)

1
y = 8.5737e-0.17x

0.1
0 2 4 6 8 10 12 14 16 18 20
Time (hr)
(1) From the equation of best fit line shown within the figure: first find k then t1/2
The value of rate constant k is equal to 0.17 hr-1 (from the equation)
t1/2 = 0.693/ 0.17 = 4.07 hr

Alternative method if the equation is not written within the equation then
first find t1/2 from graph the then calculate k
from the data plotted on semilog graph paper use two points from the line of
best fit
To find t1/2 from the graph
10
Plasma concentration (µg/mL)

0.1
0 2 4 6 8 10 12 14 16 18 20
Time (hr)
3. A new drug was given in a single intravenous
dose of 200 mg to an 80-kg adult male
patient. After 6 hours, the plasma drug
concentration of drug was 1.5 mg/100 mL of
plasma. Assuming that the apparent VD is 10%
of body weight, compute the total amount of
drug in the body fluids after 6 hours. What is
the half-life of this drug?
4. A new antibiotic drug was given in a single intravenous
bolus of 4 mg/kg to five healthy male adults ranging in
age from 23 to 38 years (average weight 75 kg). The
pharmacokinetics of the plasma drug concentration-
time curve for this drug fits a one-compartment model.
The equation of the curve that best fits the data is
Cp = 78 e-0.46t
Determine the following (assume units of ug/mL for C p
and hr for t):
a. What is the t 1/2
b. What is the VD
c. What is the plasma level of the drug after 4 hours?
Residual method to calculate area
under the curve
For iv one compartment model

K = slope x -2.3
Plasma level (Cp)

Slope = Δ y / Δ x = (log Cp2 – log Cp1) / (t2 – t1)


Log scale

Time

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