Algorithm (geometric progression) [Design Issues]

posted by intuitivepharma – India, 2013-02-28 09:10 (4046 d 14:57 ago) – Posting: # 10127
Views: 9,126

Dear Helmut,

I sincerely apologise for reopening an old discussion thread. However I found it very tempting and interesting to come across an algorithm, to generate sampling time points as per a geometric progression.

I tried to emulate your algorithm to generate sampling time points as per a geometric progression in excel. Unfortunately I am unable to generate the time points. Can you please help me with the excel code for the same?

Formula I used was,
Ti = (B4-1)*((B2/B1)^(1/(B3-1)))

First Time Point [B1]    0.0833
Last Time Point [B2]     12
No of time points [B3]   15
Index of time point [B4] 15


I understand if I had coded the algorithm correctly, then when I key in 15 at the index of time point, I should get 12 hrs as the time point. I got 19.966 instead. When I key in 1 at the index of time point, I should get 0.0833 hrs as the time point. I got 0 instead. :confused:

As indicated by you the above formula will suffice the purpose of spacing time points as per a geometric progression and the output needs to be fine tuned towards practicability and based on individual formulation characteristic.

On a more scientific basis, can I derive any input from the “partial derivatives plot” generated by WinNonlin for sampling point determination? The WinNonlin write-up on the same is not very comprehensive. Kindly throw some light on the same.

For example kindly consider the following plasma concentration time profile.

Time    Concentration
0       0
0.5     27.91
1       47.27
2       69.61
3       79.52
4       83.25
5       83.93
6       83.11
9       77.72
12      71.67
16      64.17
24      51.41
36      36.86
48      26.43
72      13.58


Its kinetic profile fits into a first order single compartment system. The Observed Y and Predicted Y vs X plot for the same is shown below.

[image]

The partial derivatives plot plot for the same is shown below.

[image]

Based on the partial derivatives plot [with information on Ka, Kel and VD] can you please guide how to optimise the sampling time points?

The idea is to generate the final time points based on geometric progression and fine tuning it with the inputs from partial derivatives plot.

Thanks
IP

Thanks & Regards,
IP.

Complete thread:

UA Flag
Activity
 Admin contact
22,957 posts in 4,819 threads, 1,636 registered users;
80 visitors (0 registered, 80 guests [including 8 identified bots]).
Forum time: 00:07 CET (Europe/Vienna)

Nothing shows a lack of mathematical education more
than an overly precise calculation.    Carl Friedrich Gauß

The Bioequivalence and Bioavailability Forum is hosted by
BEBAC Ing. Helmut Schütz
HTML5