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A GENERAL question for the group... In planning a PK study where patients
receive a drug for 15 days, assuming that they are at steady state, could
you do serial draws on day 14, over almost the entire 24 hours between day
14 and 15, and then do some other decay draws 3, 7, and 14 days after
finishing the drug? It seems to me that even though the person would be at
steady state, on day 14, that the day 15 dose of the drug would be a
confounding factor for those 3, 7, and 14 day draws. Does what I'm asking
you make sense?
Thanks,
C. David Claghorn, Pharm.D.
Director, Nonclinical Reports & Submissions
ILEX Oncology
(210)949-8339
e-mail:dclaghorn.at.ilexonc.com
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[A few replies - db]
From: "Loewen, Gordon"
To: "'PharmPK.-at-.pharm.cpb.uokhsc.edu'"
Subject: RE: PharmPK A design question
Date: Fri, 11 Dec 1998 15:02:38 -0800
X-Priority: 3
MIME-Version: 1.0
David
Kudos for you for sensing something wasn't quite right. Of course the
answer to your question is "it all depends".
If you are modeling the data - you simply need to let the modeling
program know the exact time (days, hours) of all the doses the patient
received (including the Day 15 dose) and the exact time of all the
samples and it should deal with the post-dose samples correctly -even
though the detailed profiling was done on Day 14.
If, like many of us, you prefer non-compartmental analysis, you have a
problem - but one that can be dealt with a few assumptions. As you
sensed, the day 18 (15 + 3), 22 and 29 samples cannot be expected to be
an extension of the Day 14 serial sampling, due to the Day 15 dose. If
you truly believe you are at steady-state, and you truly believe that
your Day 14 sampling has not perturbed the system, you may want to
assume that the Day 15 profile would have been identical to the Day 14
profile (or conversely, that the Day 18, 22, and 29 samples would have
been identical to the Day 17, 21 and 28 samples), and conduct the
analysis with the amended sample times. As always, if you make an
assumption, be sure to detail it in any reports you prepare with the
data.
Gord
---
From: "Loewen, Gordon"
To: "'PharmPK.-at-.pharm.cpb.uokhsc.edu'"
Subject: FW: PharmPK A design question
Date: Fri, 11 Dec 1998 15:09:56 -0800
X-Priority: 3
MIME-Version: 1.0
Woops - forgot my math - the last parenthetical line should be: (or
conversely, that the Day 18, 22, and 29 samples would have been
identical to the Day 19, 23 and 30 samples),
---
From: DGarg8838.-at-.aol.com
Date: Sun, 13 Dec 1998 18:28:08 EST
To: PharmPK.aaa.pharm.cpb.uokhsc.edu
Mime-Version: 1.0
Subject: Re: PharmPK A design question
I do not understand the rationale for doing serial draws on Day 14 when the
drug is going to be administered until Day 15. Why not do the serial draws on
the last day of drug administration. If the half life of the drug is long then
samples can be drawn on other days (days 3, 7, 10 after the last dose). You
should also consider doing the serial blood samples after the first dose to
get pharmacokinetic profile both after single dose and at steady state.
Dyal Garg
561-737-3954
Fax: 561-732-1941
Dgarg8838.-at-.aol.com
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