Calculate the half-life of the antibiotic Ofloxacin in this patient

[havenly]

Homework Statement

half life time

Relevant Equations

𝑇1/2 =(𝑙𝑛2) 𝑥 𝑉𝑜𝑙𝑢𝑚𝑒 𝑑𝑒 𝑑𝑖𝑠𝑡𝑟𝑖𝑏𝑢𝑡𝑖𝑜𝑛/ clarence.

A 70 kg patient is treated with ciprofloxacin (2 x 500 mg / d) for an infection
pulmonary. Ciprofloxacin is an antibiotic eliminated primarily by the kidneys, its
apparent volume of distribution is 3 [1 / kg) and its clearance is 0.5 (Wh x kg).
Calculate the half-life of ofloxacin in this patient. Later, his situation
degrades: it produces edema and the volume of distribution of ofloxacin increases to 125 liters.
After calculating the new half-life of ofloxacin in this patient,
Choose
the correct statement among the following 5:
Please choose an answer:
A. The half-life is extended by 60 min. NS.
B. The half-life is shortened by 30 min. NS.
C. The half-life is lengthened by 4h10 min. NS.
D. The half-life time remains unchanged.
E. The half-life is extended by 100 min. NS.to calculate the first half-life I did:

T1/2 =(ln(2) x volume distribution)/ clearance

v=70Kg x 3L/KG =210L
clearance 0.5L/H KG x70KG=35

T1/2= (ln(2) x 210)/ 35 = 4.158h

to calculate the second half-life:

k= ln(2) / T1/2
K= ln2/4.158 =0.166

clearance= K. V
clearance= 0.166 X 125= 20.83

T1/2= (ln (2) x125)/ 20.83 =4.158h

I get that the half-life time remains the same; I don't see where my error is. you can help me?

 

[anuttarasammyak]

I am layman in medicine and chemistry. As I have scarce knowledge on your system mechanism half time you say reminds me exponential decay as radioactive materials.

 

[Steve4Physics]

Homework Statement:: half life time
Relevant Equations:: 𝑇1/2 =(𝑙𝑛2) 𝑥 𝑉𝑜𝑙𝑢𝑚𝑒 𝑑𝑒 𝑑𝑖𝑠𝑡𝑟𝑖𝑏𝑢𝑡𝑖𝑜𝑛/ clarence.

A 70 kg patient is treated with ciprofloxacin (2 x 500 mg / d) for an infection
pulmonary. Ciprofloxacin is an antibiotic eliminated primarily by the kidneys, its
apparent volume of distribution is 3 [1 / kg) and its clearance is 0.5 (Wh x kg).
Calculate the half-life of ofloxacin in this patient. Later, his situation
degrades: it produces edema and the volume of distribution of ofloxacin increases to 125 liters.
After calculating the new half-life of ofloxacin in this patient,
Choose
the correct statement among the following 5:
Please choose an answer:
A. The half-life is extended by 60 min. NS.
B. The half-life is shortened by 30 min. NS.
C. The half-life is lengthened by 4h10 min. NS.
D. The half-life time remains unchanged.
E. The half-life is extended by 100 min. NS.to calculate the first half-life I did:

T1/2 =(ln(2) x volume distribution)/ clearance

v=70Kg x 3L/KG =210L
clearance 0.5L/H KG x70KG=35

T1/2= (ln(2) x 210)/ 35 = 4.158h

to calculate the second half-life:

k= ln(2) / T1/2
K= ln2/4.158 =0.166

clearance= K. V
clearance= 0.166 X 125= 20.83

T1/2= (ln (2) x125)/ 20.83 =4.158h

I get that the half-life time remains the same; I don't see where my error is. you can help me?

Hi @havenly. Welcome to PF.

I’m sure someone here can help, but there are some problems with your question. Using my limited knowledge, here is a list of the problems I spotted. If you can fix them, you are more likely to get help.

1. Does (2 x 500 mg / d) mean a single dose of 1000mg? If not, what does it mean?

2. You have given the apparent volume of distribution as “3 [1 / kg) “. This makes no sense. Apparent volume of distribution should be in units of litres (l). I guess you mean ‘apparent volume of distribution per kg of body mass” (= 3 l/kg). Is that what you mean?

3. You said “clearance is 0.5 (Wh x kg)” but that makes no sense, Clearance is typically measured in units of l/h. Do you mean “clearance per kg of body mass” which has units of l/(h.kg)?

4. You changed “ciprofloxacin” to “ofloxacin” halfway through the question. They are different antibiotics. Is that a mistake?

5. The question says new volume of distribution increases to 125 litres. Do you means 125 litres or 125 litres/kg?. I.e. is 125 in the same units as the initial value (3 l/kg)?

6. When the volume of distribution increases to 125 litres, does the clearance stay the same or change?

7. What do the letters ‘NS’ stand for, in the list of alternative answers?

I’m guessing your question has been translated from another language (French?) which could be the reason for some of the problems.