RE: TVKa>TVKe or Ka>Ke?
From: Ken Kowalski <Ken.Kowalski@pfizer.com>
Subject: RE: [NMusers] TVKa>TVKe or Ka>Ke?
Date: 8/8/2003 8:16 AM
Justin,
If this is the case, given that there is approximately a 10-fold difference
in your estimates of TVKa and TVKe, you must be getting an extremely large
estimate for the IIV of Ka in order for some individuals' Ka to be smaller
than Ke. For those individuals where Ka < Ke what is the value of Ke? If
it is considerably larger and closer to the population estimate of Ka (TVKa)
then I would still be suspicious that you're getting flip-flop. On the
other hand, if the individual estimate of Ke is closer to the population
mean estimate of Ke (TVKe) and for some individuals the Ka just happens to
be even lower (ie., both Ka and Ke are small but Ka<Ke) then I would
probably agree with you that they are indeed slow absorbers. If you truly
have a sub-population of slow absorbers, a histogram of the etas for Ka
should be skewed and/or bi-modal. In this case I would investigate
covariates (e.g., food) that might influence Ka or consider a mixture model.
Ken