A pharmacokinetic problem

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VO - 06 May 2004 01:55 GMT

Hi,

Please help me in solving the following problem.....I just can't seem
to get something right in it...Thanks in advance.

JB 38 Yr old non smoker with COPD who is started on theophylline in
the ER. A loading dose of 300 mg is administered over 30 min.Blood
ssamples obtained 3hrs and 6hrs after the loading dose revealed serum
concentrations of 12mg/L and 8.1 mg/L,respectively.

The elimination half life of theophylline in this patient is:
ans choices: 0.53hrs, 5.33hrs, 3.5hrs,,6.00hrs.

Please post the method / formulae too, used to solve the above
problem.

Regards.

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Gregory Poon - 06 May 2004 05:24 GMT

This sounds like a assignment ... here's a blatant hint but work it out
yourself.

In the question you are given concentrations at two different times: c(3h) =
12 mg/L and c(6h) = 8.1 mg/L. If you can assume a simple one-compartment
model and elimination follows a single exponential decay:

c(3) = c(0)*exp(-3*k)
c(6) = c(0)*exp(-6*k)

where time is taken to be hours so k is in units 1/hour. Two equations, two
unknowns, so now it's just simple algebra. And once you have k, t1/2 is a
snap.

Signature

Gregory M. K. Poon, Ph.D., R.Ph., B.Sc.Phm.
Departments of Pharmaceutical Sciences and Chemical Engineering
University of Toronto

> Hi,
>
[quoted text clipped - 13 lines]
>
> Regards.

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VO - 06 May 2004 18:40 GMT

Dr. Poon,

Thanks for the help.

That was one of the problems I have been solving for practice for an
exam. And I was getting confused about the Loading dose and the
infusion rate....

I appreciate your answer.

Thanks.

> This sounds like a assignment ... here's a blatant hint but work it out
> yourself.
[quoted text clipped - 27 lines]
> >
> > Regards.

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Dr. Wayne Simon - 06 May 2004 21:10 GMT

> Hi,
>
[quoted text clipped - 13 lines]
>
> Regards. Was it 300 mg of theophylline or 300 mg of theophylline

ethylaminediamine. ?

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