Re: rounding issues with PK data
Hi Nele,
For the first point, if you have values that are rounded like that and you will
be mixing rounded and non-rounded values, then the simplest way to handle it
would be to have a different additive error term for measurements that were or
were not subject to the rounding.
A more complex method would be to implement something akin to the M2 method but
using both a lower and upper limit for the range of values that would be mapped
to each value in the file. The higher complexity is unlikely to be worth it.
With the sampling times only being documented as dates, to give the full
answer, we'd need more information: is there a non-terminal phase to the
half-life that extends beyond the first day? Is the terminal half-life > ~5
days? What is there a need for more precision than 1 day resolution to the
half-life and is it possible (i.e. even if you had data down to the second,
would your SE be <1 day for half-life)?
Generally, if the half-life is more than about 5 days, there should be no major
issue with only having dates of collection.
Thanks,
Bill
Quoted reply history
On Jun 10, 2013, at 2:57, "Kaessner, Nele"
<[email protected]<mailto:[email protected]>> wrote:
Dear nmusers,
I have PK data from a compound with a very long half-life (weeks). I have two
issues with this data and would very much like to hear your opinion on this:
· Concentrations were rounded to integers, with LLOQ of 1. This means a
concentration value of 2 could span values from 1.5-2.49, and unfortunately
there is no way to find out what was originally measured, and I have quite a
few measurements around LLOQ. How would you handle this in the coding (also
later when mixing with additional data that was not rounded), and how will this
rounding influence my parameter estimates?
· The sampling times were only documented as dates (except for the day
of dosing). With a long half-life compound, do you consider this to be critical?
Your opinions would be very welcome.
Best regards
Nele
______________________________________________________________
Dr. Nele Käßner
Principal Scientist Modeling and Simulation
Global Pharmacometrics
Experimental Medicine
Takeda Pharmaceuticals International GmbH
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8152 Glattpark-Opfikon (Zürich)
Switzerland
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