TimeLow [R for BE/BA]

posted by Astea – Russia, 2017-10-28 22:15 (1546 d 00:14 ago) – Posting: # 17938
Views: 20,488

Dear smart people!

Can anyone please suggest me an easy way of calculation T50% early and late, T75%, T90% and similar parameters via Phoenix?

To this time I could only find this old thread deducated to Therapeutic Response Module. But following this module we can only get TimeLow, TimeHigh or TimeDuring in the output of pharmacokinetical parameters.

Imagine we have an ideal standard curve, than TimeLow=T50%early+T-T50%late, TimeDuring=T50%late-T50%early (here T is the total duration of observation). So it is impossible to get T50%ealy and T50%late separately from this data. To deal with it I had to delete data after Tmax for calculating T50%early or before Tmax for calculating T50%late.

By the way, in this old thread as well as in this it was written that Phoenix approximates the decreasing part with log-transformation independetly of the rule choosen for AUC. Now it seemed to be changed, and the actual form of approximation depends on the rule for AUC, so it can be linear as well as log-linear. But this is not true for partial area calculation: for example, AUC0-72 for subjects with missing t=72 value, Phoenix always do log interpolation even if we've choosen linear AUC calculation.

Returning to TimeLow calculation. I am also puzzled why for the following dataset we get TimeLow=18 if Lower limit is choosen to be 3? Because if we substract 4 from all time points we'll get 16... (linear interpolation was selected)

   t | C
  4  | 6
  6  | 4
  8  | 3
  10 | 2
  12 | 0
  24 | 0

"Being in minority, even a minority of one, did not make you mad"

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