# Accumulation ratio after multiple dosing

**URL:** <https://forum.certara.com/t/accumulation-ratio-after-multiple-dosing/3132>\
**Category:** Phoenix WNL basics\
**Created:** [February 14, 2017, 6:56pm UTC](https://forum.certara.com/t/accumulation-ratio-after-multiple-dosing/3132 "2017-02-14T18:56:25Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![llli](https://avatars.discourse-cdn.com/v4/letter/l/b9bd4f/32.png) [@llli](https://forum.certara.com/u/llli)\
**Post date:** [February 14, 2017, 6:56pm UTC](https://forum.certara.com/t/accumulation-ratio-after-multiple-dosing/3132/1 "2017-02-14T18:56:25Z")

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Hi all,

I have a question about the calculation of accumulation ratio after multiple dosing in NCA.

If the study drug was given daily from Day 1 to 10 and the PK samples were collected on Day 1 and Day 10, I got two lambda\_z from both Day 1 and Day 10. It looks like that the WinNonlin uses the lambda-z on Day 10 to calculate the accumulation ratio after multiple dosing: R=1/(1-e-lambda\_z\*24).

My question is which lambda\_z should be used for the accumulation ratio calculation? Any input is appreciated!

Thank you!

LLLi

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**Author:** ![SimonDavis](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@SimonDavis](https://forum.certara.com/u/SimonDavis)\
**Post date:** [February 14, 2017, 7:54pm UTC](https://forum.certara.com/t/accumulation-ratio-after-multiple-dosing/3132/2 "2017-02-14T19:54:51Z")

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Hi LLLi, the accumulation ratio formula used by WNL is because sometimes only the steady state profile is processed in NCA so there is no easy way for it to calculate the actual accumulation seen.

if you do have data from the single dose day and the steady state day then you can very easily merge the results from these different days together (so they are on the same row in the work sheet) and then calculate e..g. AUCtauSS/AUCtau\_D1 in a data wizard.

this was discussed some time ago;

[https://support.certara.com/forums/topic/34-how-to-calculate-ratios-between-parameters-egauc/?hl=ratio](https://support.certara.com/forums/topic/34-how-to-calculate-ratios-between-parameters-egauc/?hl=ratio)

Simon.

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**Author:** ![mittyright](https://avatars.discourse-cdn.com/v4/letter/m/e9a140/32.png) [@mittyright](https://forum.certara.com/u/mittyright)\
**Post date:** [February 14, 2017, 10:46pm UTC](https://forum.certara.com/t/accumulation-ratio-after-multiple-dosing/3132/3 "2017-02-14T22:46:13Z")

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Hi LLLi,

regarding accumulation ratio I highly recommend to study the following topic thoroughly:

[http://forum.bebac.at/mix\_entry.php?id=3954](http://forum.bebac.at/mix_entry.php?id=3954)

Mittyright