# Certara Forums **URL:** https://forum.certara.com/c/phoenix/certara-forums/23.md [Latest](https://forum.certara.com/latest.md) · [Categories](https://forum.certara.com/categories.md) · [Tags](https://forum.certara.com/tags.md) --- ## [About the Certara Forums category](https://forum.certara.com/t/about-the-certara-forums-category/4120)
**Author:** [@system](https://forum.certara.com/u/system)\ **Replies:** 0\ **Last updated:** [March 24, 2025, 2:28am UTC](https://forum.certara.com/t/about-the-certara-forums-category/4120 "2025-03-24T02:28:54Z")
--- ## [How to code a fixed additive residual error without freeze (and keep FOCE-ELS available)](https://forum.certara.com/t/how-to-code-a-fixed-additive-residual-error-without-freeze-and-keep-foce-els-available/4432)
**Author:** [@Stephen\_Duffull](https://forum.certara.com/u/Stephen_Duffull)\ **Replies:** 0\ **Last updated:** [October 19, 2026, 3:47am UTC](https://forum.certara.com/t/how-to-code-a-fixed-additive-residual-error-without-freeze-and-keep-foce-els-available/4432 "2026-10-19T03:47:39Z")
If you need one component of a combined (proportional + additive) residual error to be a fixed constant — the natural instinct is error(CEpsAdd(freeze) = value). Worth knowing before you do that: freezing an error()/sigm… --- ## [NCA Multiple Dose with Different Dosing Interval - Feasible within WNL?](https://forum.certara.com/t/nca-multiple-dose-with-different-dosing-interval-feasible-within-wnl/3693)
**Author:** [@aramisrojas](https://forum.certara.com/u/aramisrojas)\ **Replies:** 1\ **Last updated:** [September 17, 2026, 5:44pm UTC](https://forum.certara.com/t/nca-multiple-dose-with-different-dosing-interval-feasible-within-wnl/3693 "2026-09-17T17:44:21Z")
Hello everybody, I’m running an NCA for the following study design for a customer: Phase 1 randomized study to assess pharmacokinetics of multiple (MAD) ascending doses of oral drug X in healthy participants. The endp… --- ## [Covariate exploration in crossover model](https://forum.certara.com/t/covariate-exploration-in-crossover-model/4413)
**Author:** [@Bruno\_Pypendop](https://forum.certara.com/u/Bruno_Pypendop)\ **Replies:** 6\ **Last updated:** [August 4, 2026, 10:04pm UTC](https://forum.certara.com/t/covariate-exploration-in-crossover-model/4413 "2026-08-04T22:04:24Z")
I have a PK model for which I would like to include a period (occasion) effect then explore whether a categorical covariate may also have an effect. There is overlap since the categorical covariate is related to the admi… --- ## [Follow for Latest Phoenix release information](https://forum.certara.com/t/follow-for-latest-phoenix-release-information/3495)
**Author:** [@SimonDavis](https://forum.certara.com/u/SimonDavis)\ **Replies:** 24\ **Last updated:** [June 24, 2026, 10:17am UTC](https://forum.certara.com/t/follow-for-latest-phoenix-release-information/3495 "2026-06-24T10:17:55Z")
Hopefully everyone received the email yesterday announcing that 8.3 is now available; https://lp.certara.com/Download-Phoenix-8.3.html Once you install this you may look under the help menu to find the release notes an… --- ## [How to change the range of the x and y axis on plots like iPRED vs. IWRES?](https://forum.certara.com/t/how-to-change-the-range-of-the-x-and-y-axis-on-plots-like-ipred-vs-iwres/4405)
**Author:** [@\_Laboratory\_for\_Syst](https://forum.certara.com/u/_Laboratory_for_Syst)\ **Replies:** 1\ **Last updated:** [June 9, 2026, 4:46pm UTC](https://forum.certara.com/t/how-to-change-the-range-of-the-x-and-y-axis-on-plots-like-ipred-vs-iwres/4405 "2026-06-09T16:46:16Z")
Right now, all of the outputs are plotted on the same axes, but they clearly shouldn’t. How can I adjust the axes to better represent the outputs, which are on different scales? --- ## [Phoenix version 8.8 has been released](https://forum.certara.com/t/phoenix-version-8-8-has-been-released/4387)
**Author:** [@SimonDavis](https://forum.certara.com/u/SimonDavis)\ **Replies:** 0\ **Last updated:** [May 1, 2026, 11:09am UTC](https://forum.certara.com/t/phoenix-version-8-8-has-been-released/4387 "2026-05-01T11:09:33Z")
Hello all! Phoenix version 8.8 has been released and is now available for download https://certara-phoenix.s3.us-east-1.amazonaws.com/Phoenix\_8.8.zip \> Do read the documentation and release notes for Phoenix 8.8 to ens… --- ## [PK-PD model of Binary repsonse](https://forum.certara.com/t/pk-pd-model-of-binary-repsonse/3630)
**Author:** [@ygsla](https://forum.certara.com/u/ygsla)\ **Replies:** 5\ **Last updated:** [April 20, 2026, 8:42pm UTC](https://forum.certara.com/t/pk-pd-model-of-binary-repsonse/3630 "2026-04-20T20:42:47Z")
HI Folks, Can we develop PK-PD model with binary reponse data in NLME? If yes, sharing some more information or suggestion or any built template will be appreciated. Thanks in advance!! Regards, Ygs --- ## [Using observed baselines values as fixed parameter value](https://forum.certara.com/t/using-observed-baselines-values-as-fixed-parameter-value/3723)
**Author:** [@cmukashyaka](https://forum.certara.com/u/cmukashyaka)\ **Replies:** 2\ **Last updated:** [March 6, 2026, 5:15pm UTC](https://forum.certara.com/t/using-observed-baselines-values-as-fixed-parameter-value/3723 "2026-03-06T17:15:07Z")
Hello, I am working on an indirect response model (limited inhibition of Kin), I have baseline values for each subject measured at the start of study. I need to use these values and fix them as E0 where E0 = Kin/Kout so… --- ## [NCA Results Plots](https://forum.certara.com/t/nca-results-plots/3698)
**Author:** [@beqool](https://forum.certara.com/u/beqool)\ **Replies:** 4\ **Last updated:** [January 28, 2026, 9:50pm UTC](https://forum.certara.com/t/nca-results-plots/3698 "2026-01-28T21:50:59Z")
Hello all! When doing an NCA in Phoenix WinNonlin the maximum number of plots shown under “Results\>\>Plots\>\>Observed Y and Predicted Y vs X” is 100. When sample size is large enough (N\>50 in a 2-period designs, N\>33 in 3… --- ## [Phoenix's new licensing system with 8.5+ https://my.certara.net](https://forum.certara.com/t/phoenixs-new-licensing-system-with-8-5-https-my-certara-net/3748)
**Author:** [@SimonDavis](https://forum.certara.com/u/SimonDavis)\ **Replies:** 6\ **Last updated:** [January 22, 2026, 1:35pm UTC](https://forum.certara.com/t/phoenixs-new-licensing-system-with-8-5-https-my-certara-net/3748 "2026-01-22T13:35:55Z")
Hopefully you have now all seen announcements about Phoenix 8.5, a key part of this new release is Certara moving away from the old Sentinel licensing system, so no more activation codes ! Phoenix 8.5 and later versions… --- ## [Efficiently Calculating Cmax and AUC with 95% CI for 5th, 50th, and 95th Quartiles in Large Phoenix NLME Simulations](https://forum.certara.com/t/efficiently-calculating-cmax-and-auc-with-95-ci-for-5th-50th-and-95th-quartiles-in-large-phoenix-nlme-simulations/4357)
**Author:** [@Bhim\_Bahadur](https://forum.certara.com/u/Bhim_Bahadur)\ **Replies:** 5\ **Last updated:** [January 20, 2026, 9:00pm UTC](https://forum.certara.com/t/efficiently-calculating-cmax-and-auc-with-95-ci-for-5th-50th-and-95th-quartiles-in-large-phoenix-nlme-simulations/4357 "2026-01-20T21:00:43Z")
Hi Users and Experts, I used Phoenix NLME to simulate concentration–time (CT) profiles for 56 subjects with 1000 replicates each, over 672 hours with 1‑hour sampling. This produced a dataset of ~37 million rows. Phoenix… --- ## [Question regarding Parameter Freezing for Simulation: Should I fix both Fixed and Random Effects?](https://forum.certara.com/t/question-regarding-parameter-freezing-for-simulation-should-i-fix-both-fixed-and-random-effects/4353)
**Author:** [@Virunya\_Komenkul](https://forum.certara.com/u/Virunya_Komenkul)\ **Replies:** 2\ **Last updated:** [January 20, 2026, 7:48am UTC](https://forum.certara.com/t/question-regarding-parameter-freezing-for-simulation-should-i-fix-both-fixed-and-random-effects/4353 "2026-01-20T07:48:01Z")
Hi everyone, I am currently working on a simulation step using my final PK/PD model in Phoenix NLME. I have a question regarding the best practice for “freezing” parameters before running the simulation. When transitio… --- ## [Phoenix NLME simulation issue](https://forum.certara.com/t/phoenix-nlme-simulation-issue/4355)
**Author:** [@sylim](https://forum.certara.com/u/sylim)\ **Replies:** 6\ **Last updated:** [January 9, 2026, 8:48pm UTC](https://forum.certara.com/t/phoenix-nlme-simulation-issue/4355 "2026-01-09T20:48:01Z")
Hi, I added two simulation tables in Phoenix NLME. Table 01 uses continuous time points: seq(0,336,0.5), Table 02 uses specific time points at 310, 312, 314, etc. The simulated concentrations in Table 01 and Table 02 we… --- ## [Allometric scaling animal to human](https://forum.certara.com/t/allometric-scaling-animal-to-human/3412)
**Author:** [@harishkaushik](https://forum.certara.com/u/harishkaushik)\ **Replies:** 2\ **Last updated:** [December 16, 2025, 5:56pm UTC](https://forum.certara.com/t/allometric-scaling-animal-to-human/3412 "2025-12-16T17:56:46Z")
Hello, I have preclinical PK data from 4 species (Mice,Rat,GuineaPig & Dog) i wanted to utilise the phoenix automation for predicting FIH dose and profile, I viewed the webinar by Serge it was helpful, but is there any… --- ## [Mixture Models with latent covariate with NLME](https://forum.certara.com/t/mixture-models-with-latent-covariate-with-nlme/4339)
**Author:** [@phychadelicpk](https://forum.certara.com/u/phychadelicpk)\ **Replies:** 1\ **Last updated:** [October 24, 2025, 6:13pm UTC](https://forum.certara.com/t/mixture-models-with-latent-covariate-with-nlme/4339 "2025-10-24T18:13:45Z")
Hi all, I am looking to reproduce a model that college developed in Monolix. They used a mixture model with a latent covariate. In my search of the manual, I see no ability to do this in NLME. I saw this confirmed by a … --- ## [Multiple oral dose population PK model](https://forum.certara.com/t/multiple-oral-dose-population-pk-model/4336)
**Author:** [@sabdulm1](https://forum.certara.com/u/sabdulm1)\ **Replies:** 2\ **Last updated:** [October 21, 2025, 4:46pm UTC](https://forum.certara.com/t/multiple-oral-dose-population-pk-model/4336 "2025-10-21T16:46:37Z")
Hello, I have a PK model for a drug that is dosed once a day for three days. I have modeled the first dose well with an enterohepatic recirculation model. I want to try adding the other two doses now. I have in my origi… --- ## [Why do i have .phxlastload or .phxbackup files being created](https://forum.certara.com/t/why-do-i-have-phxlastload-or-phxbackup-files-being-created/4337)
**Author:** [@SimonDavis](https://forum.certara.com/u/SimonDavis)\ **Replies:** 0\ **Last updated:** [October 21, 2025, 9:53am UTC](https://forum.certara.com/t/why-do-i-have-phxlastload-or-phxbackup-files-being-created/4337 "2025-10-21T09:53:29Z")
i’ve had a few people ask about these and I thought it would be useful to point people to these two tip pages - essentially you can ignore them unless you need to return to previous version of a project. it’s not a repla… --- ## [How to exclude Predose from being identified as Cmax in Phoenix](https://forum.certara.com/t/how-to-exclude-predose-from-being-identified-as-cmax-in-phoenix/4325)
**Author:** [@John\_CK\_Lai](https://forum.certara.com/u/John_CK_Lai)\ **Replies:** 2\ **Last updated:** [October 9, 2025, 9:32pm UTC](https://forum.certara.com/t/how-to-exclude-predose-from-being-identified-as-cmax-in-phoenix/4325 "2025-10-09T21:32:57Z")
Hi all, I received a single dose plasma concentration-time dataset (n=50 subjects) that I will be using NCA in Phoenix to generate the standard PK parameters. The compound of interest is endogenous so there is existing… --- ## [Follow for Integral release updates](https://forum.certara.com/t/follow-for-integral-release-updates/4331)
**Author:** [@SimonDavis](https://forum.certara.com/u/SimonDavis)\ **Replies:** 0\ **Last updated:** [October 6, 2025, 10:00am UTC](https://forum.certara.com/t/follow-for-integral-release-updates/4331 "2025-10-06T10:00:44Z")
Most of you should have received this information by email at the beginning of September, but I reiterate it below to share information about 25.10.1, the next release of Certara Integral. Integral 25.10.1 Scope Integr… --- ## [PK Submit releases, new plug-in to create PK CDISC Domain](https://forum.certara.com/t/pk-submit-releases-new-plug-in-to-create-pk-cdisc-domain/3424)
**Author:** [@SimonDavis](https://forum.certara.com/u/SimonDavis)\ **Replies:** 4\ **Last updated:** [September 30, 2025, 10:28am UTC](https://forum.certara.com/t/pk-submit-releases-new-plug-in-to-create-pk-cdisc-domain/3424 "2025-09-30T10:28:33Z")
In this 30-minute webinar, you will learn about PK Submitâ„¢, a new add-on to Phoenix WinNonlin that automates the creation of PK CDISC domains during NCA analysis. It can generate both Study Data Tabulation Model (SDTM)… --- ## [European Phoenix User Group Meetings](https://forum.certara.com/t/european-phoenix-user-group-meetings/3655)
**Author:** [@SimonDavis](https://forum.certara.com/u/SimonDavis)\ **Replies:** 3\ **Last updated:** [August 29, 2025, 11:27am UTC](https://forum.certara.com/t/european-phoenix-user-group-meetings/3655 "2025-08-29T11:27:07Z")
Please consider attending this meeting to hear about our vision for the future of the Phoenix platform and how we plan to continue to support our customers in their digital transformation Keynote speakers Dr. Cardot a… --- ## [RSABE - 95%UCB estimation for Highly variable Drugs\_FDA](https://forum.certara.com/t/rsabe-95-ucb-estimation-for-highly-variable-drugs-fda/3576)
**Author:** [@d\_nil](https://forum.certara.com/u/d_nil)\ **Replies:** 5\ **Last updated:** [August 29, 2025, 11:21am UTC](https://forum.certara.com/t/rsabe-95-ucb-estimation-for-highly-variable-drugs-fda/3576 "2025-08-29T11:21:14Z")
Dear Team, Is there any provision to determine Reference scaled average bioequivalence for Highly variable drugs? In which, We are interested to calculate 95% Upper confidence bound. The parameter in which we are inter… --- ## [How to appropriately cite Phoenix products](https://forum.certara.com/t/how-to-appropriately-cite-phoenix-products/2804)
**Author:** [@vivaturi](https://forum.certara.com/u/vivaturi)\ **Replies:** 7\ **Last updated:** [August 29, 2025, 8:09am UTC](https://forum.certara.com/t/how-to-appropriately-cite-phoenix-products/2804 "2025-08-29T08:09:53Z")
Can someone provide a standard way to cite the use Phoenix in reports/publications etc. Is it different for citing NLME vs NCA vs IVIVC etc.. Thanks Vijay --- ## [Pirana 25.7.1 Release Announcement](https://forum.certara.com/t/pirana-25-7-1-release-announcement/4319)
**Author:** [@kniefort](https://forum.certara.com/u/kniefort)\ **Replies:** 1\ **Last updated:** [August 12, 2025, 5:48pm UTC](https://forum.certara.com/t/pirana-25-7-1-release-announcement/4319 "2025-08-12T17:48:15Z")
We are very pleased to announce the release of Pirana 25.7.1! Pirana is a pharmacometrics (PMX) workbench solution that coordinates the use of multiple tools to add efficiency, organization, and quality to PMX workflows… --- ## [Units in Phoenix Modeling](https://forum.certara.com/t/units-in-phoenix-modeling/2585)
**Author:** [@jdeng415](https://forum.certara.com/u/jdeng415)\ **Replies:** 4\ **Last updated:** [August 4, 2025, 3:04am UTC](https://forum.certara.com/t/units-in-phoenix-modeling/2585 "2025-08-04T03:04:07Z")
Dear Experts, When using pheonix to model data, I have found that sometimes the units in the “theta” results worksheet does not always come out right. How do you specify units in pheonix modeling? I know that you can use… --- ## [Changing Output units for V and Cl](https://forum.certara.com/t/changing-output-units-for-v-and-cl/2295)
**Author:** [@jmcdowell](https://forum.certara.com/u/jmcdowell)\ **Replies:** 7\ **Last updated:** [July 18, 2025, 9:20pm UTC](https://forum.certara.com/t/changing-output-units-for-v-and-cl/2295 "2025-07-18T21:20:18Z")
Dear All, this seems like such a silly question but I can’t seem to find the answer in any documentation. My input is conc in ng/mL and time is in minutes so I’m getting V in mL and Cl in mL/min. However, I desire the re… --- ## [ℹ️ New Pirana Certification Course - Starts 25 August 2025](https://forum.certara.com/t/new-pirana-certification-course-starts-25-august-2025/4297)
**Author:** [@ana.henry](https://forum.certara.com/u/ana.henry)\ **Replies:** 0\ **Last updated:** [July 18, 2025, 5:19pm UTC](https://forum.certara.com/t/new-pirana-certification-course-starts-25-august-2025/4297 "2025-07-18T17:19:39Z")
Get certified in the used of Pirana, a powerful model management tool widely utilized in pharmacometric modeling and simulation. This is the first time that Certara University offers a Live on-line certification course … --- ## [Bioavailability of prodrug vs parent drug](https://forum.certara.com/t/bioavailability-of-prodrug-vs-parent-drug/4287)
**Author:** [@PWXYZE](https://forum.certara.com/u/PWXYZE)\ **Replies:** 1\ **Last updated:** [July 18, 2025, 11:33am UTC](https://forum.certara.com/t/bioavailability-of-prodrug-vs-parent-drug/4287 "2025-07-18T11:33:33Z")
We are looking to calculate the bioavailability of a prodrug as compared to the parent drug. We have calculated the NCA parameters for each individually (parent drug IV, parent drug PO, prodrug PO), but I’m not sure how … --- ## [Modeling between period variation](https://forum.certara.com/t/modeling-between-period-variation/4274)
**Author:** [@phychadelicpk](https://forum.certara.com/u/phychadelicpk)\ **Replies:** 5\ **Last updated:** [July 3, 2025, 9:39pm UTC](https://forum.certara.com/t/modeling-between-period-variation/4274 "2025-07-03T21:39:30Z")
Hi all, I got a bunch of studies, that include MAD and cross over studies of different dose levels. Just looking at the plots there appears to be cyp induction that you would only see in the more drawn out studies. I as… [Next page](https://forum.certara.com/c/phoenix/certara-forums/23.md?page=1)