Hi to all! t75% (aka plateau time, aka POT-25 = peak occupancy time; time interval where C >= 75% of Cmax = C within 25% of Cmax) is already a mandatory PK metric according to Russia’s GL for MR formulations. Additionally HVD (half value duration, aka POT-50; time interval where C >= 50% of Cmax = C within 50% of Cmax) is under discussion for EMA’s revised MR guideline. In PHX (NCA - Therapeutic Response) we see the ‘Min Response’ and ‘Max Response’ and can enter Lower and Upper values. Consider following simple dataset: t=0,1,2,4; C=0,100,45,20 The limit for t75% is 75 and for HVD 50. PHX interpolates linear within increasing values and semilogarithmically within decreasing values. So far, so good. The intersection points for t75% are 0.75/75 and 1.3603/75. Therefore t75% 0.6103. The intersection points for HVD are 0.50/50 and 1.8681/50. Therefore HVD 1.3681. 
If I set lower to 50 and upper to 75 I get: TimeLow 2.6319 TimeHgh 0.6103 OK, so t75% = TimeHgh, but is it always correct to assume HVD = Tlast – TimeLow (like in this simple example)? How is this value actually calculated?
Dear Helmut, There’s a description of how these parameters are calculated in the User’s Guide. Using the way you set up NCA, you can set HVD = Tlast - TimeLow. Another way to set up NCA to compute HVD for this example would be to specify only a lower bound of 50 (no upper bound). Then HVD = TimeHgh. Hope this helps, Ana