# Modelling and Simulation **URL:** https://forum.certara.com/c/phoenix/certara-forums/modelling-and-simulation/27.md?page=2 [Latest](https://forum.certara.com/latest.md) · [Categories](https://forum.certara.com/categories.md) · [Tags](https://forum.certara.com/tags.md) **Page:** 3 --- ## [PKPD modeling](https://forum.certara.com/t/pkpd-modeling/3677)
**Author:** [@vetpharma](https://forum.certara.com/u/vetpharma)\ **Replies:** 1\ **Last updated:** [April 10, 2023, 7:59pm UTC](https://forum.certara.com/t/pkpd-modeling/3677 "2023-04-10T19:59:00Z")
Hi, There is an enzyme inhibitor effect that I am trying to model. The compound A inhibits an enzyme which is responsible for metabolism of compound B. By inhibiting the enzyme, Cp of compound B increases to the therape… --- ## [Initial fcntheta1 NaN error in NLME](https://forum.certara.com/t/initial-fcntheta1-nan-error-in-nlme/3672)
**Author:** [@18963422692](https://forum.certara.com/u/18963422692)\ **Replies:** 4\ **Last updated:** [March 21, 2023, 5:44am UTC](https://forum.certara.com/t/initial-fcntheta1-nan-error-in-nlme/3672 "2023-03-21T05:44:34Z")
Dear all, I am trying to write a QSP model (See "Betts A, Haddish-Berhane N, Shah DK, van der Graaf PH, Barletta F, King L, Clark T, Kamperschroer C, Root A, Hooper A, Chen X. A Translational Quantitative Systems Pharma… --- ## [Model fitting, dissolution testing](https://forum.certara.com/t/model-fitting-dissolution-testing/3669)
**Author:** [@Chaeyeong](https://forum.certara.com/u/Chaeyeong)\ **Replies:** 1\ **Last updated:** [March 17, 2023, 10:17am UTC](https://forum.certara.com/t/model-fitting-dissolution-testing/3669 "2023-03-17T10:17:32Z")
Hi, I have a somewhat complex setup for powder dissolution testing that I would like to model in Phoenix. The issue is that I would like to be able to fit parameters on multiple levels in the model: -Some parameters I … --- ## [Metabolite gut formation](https://forum.certara.com/t/metabolite-gut-formation/3667)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 1\ **Last updated:** [March 8, 2023, 11:17pm UTC](https://forum.certara.com/t/metabolite-gut-formation/3667 "2023-03-08T23:17:09Z")
Hi, I am trying to fit a parent drug dosed orally with an active metabolite. I need to estimate the amount of the drug converted to the metabolite in the gut in addition to the amount formed by metabolite formation in pl… --- ## [\-2LL value increase with QRPEM](https://forum.certara.com/t/2ll-value-increase-with-qrpem/3666)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 1\ **Last updated:** [March 3, 2023, 6:52am UTC](https://forum.certara.com/t/2ll-value-increase-with-qrpem/3666 "2023-03-03T06:52:47Z")
Hi, I am trying to use QRPEM algorithm instead of FOCE-I but I found the value of -2ll is not decreased in iteration process but increase over time where it started around 10800 and ended close to 20101. I am not sure wh… --- ## [Two absorption compartment and ADDL](https://forum.certara.com/t/two-absorption-compartment-and-addl/3665)
**Author:** [@vetpharma](https://forum.certara.com/u/vetpharma)\ **Replies:** 4\ **Last updated:** [March 1, 2023, 12:00pm UTC](https://forum.certara.com/t/two-absorption-compartment-and-addl/3665 "2023-03-01T12:00:54Z")
Hi, I am modeling a compound that has mix of IR and SR formulations. The data are from a clinical trial with three times administration a day and sampling at day 18. I defined two absorption compartment with Tlag on the… --- ## [Intravenous infusion with two compartments](https://forum.certara.com/t/intravenous-infusion-with-two-compartments/3657)
**Author:** [@amitte](https://forum.certara.com/u/amitte)\ **Replies:** 3\ **Last updated:** [January 12, 2023, 2:27pm UTC](https://forum.certara.com/t/intravenous-infusion-with-two-compartments/3657 "2023-01-12T14:27:57Z")
Dear Certara Team I am conducting a PK analysis on a rich/dense dataset from an study with an continuous i.v. infusion over 90 minutes (no bolus). Previous NCA analysis seem to indicate distributional kinetics. The kin… --- ## [PopPK with Nested Random Effects](https://forum.certara.com/t/poppk-with-nested-random-effects/3653)
**Author:** [@djtaylor](https://forum.certara.com/u/djtaylor)\ **Replies:** 5\ **Last updated:** [December 12, 2022, 9:12am UTC](https://forum.certara.com/t/poppk-with-nested-random-effects/3653 "2022-12-12T09:12:41Z")
Hi - I am trying to fit a Pop PK model for repeat extravascular dosing and need to specify a within-subject random absorption effect (i.e., absorption varies both across subjects and within subjects over time). I’m doin… --- ## [Select residual error model and VPC plot with negative value](https://forum.certara.com/t/select-residual-error-model-and-vpc-plot-with-negative-value/3650)
**Author:** [@joybaker](https://forum.certara.com/u/joybaker)\ **Replies:** 4\ **Last updated:** [November 23, 2022, 10:20am UTC](https://forum.certara.com/t/select-residual-error-model-and-vpc-plot-with-negative-value/3650 "2022-11-23T10:20:51Z")
Hello all, I use additive\\ multiplicative\\add&mul error models to evaluate my base model. All error models can fit OK, but when I check the VPC results, the 5%/95% bounds under/overestimate the observed data for additive… --- ## [Show results at Time after "selected" dose](https://forum.certara.com/t/show-results-at-time-after-34-selected-34-dose/3651)
**Author:** [@frrd](https://forum.certara.com/u/frrd)\ **Replies:** 3\ **Last updated:** [November 22, 2022, 10:52am UTC](https://forum.certara.com/t/show-results-at-time-after-34-selected-34-dose/3651 "2022-11-22T10:52:07Z")
I have a PKPD model where I use a dosing to start a PD challenge (I dose the “effect” into an ODE). As the experiment is spanning multiple doses and weeks. I would like to display the results in TAD. My problem is that … --- ## [Modeling Extended/slow Release Formulation](https://forum.certara.com/t/modeling-extended-slow-release-formulation/3648)
**Author:** [@wafaanasser94](https://forum.certara.com/u/wafaanasser94)\ **Replies:** 2\ **Last updated:** [November 8, 2022, 1:26pm UTC](https://forum.certara.com/t/modeling-extended-slow-release-formulation/3648 "2022-11-08T13:26:06Z")
Hello, I am trying to build a pop-pk model for an extended/slow release formulation that was administered at 5 mg/kg Intraperitoneal injection ( IP ) I tried several models like Enterohepatic Recirculation , Transit mo… --- ## [Missed doses](https://forum.certara.com/t/missed-doses/3640)
**Author:** [@gew8](https://forum.certara.com/u/gew8)\ **Replies:** 13\ **Last updated:** [November 4, 2022, 7:08am UTC](https://forum.certara.com/t/missed-doses/3640 "2022-11-04T07:08:28Z")
Hi all, If I have a data set where subjects receive repeated doses, but there are several dose interruptions, how do I include this in a Phoenix data set? Do I set the missing doses to 0? The guidance isn’t clear on thi… --- ## [problem about predictive check](https://forum.certara.com/t/problem-about-predictive-check/3645)
**Author:** [@crystal](https://forum.certara.com/u/crystal)\ **Replies:** 4\ **Last updated:** [October 24, 2022, 6:57am UTC](https://forum.certara.com/t/problem-about-predictive-check/3645 "2022-10-24T06:57:20Z")
Dear all, I built a POP PK model, after I finished Predicitive check, I found the output picture was a little strange, the name of Y-axis was “DV0” instead of “DV”. Does anyone know why there was a “0” behind the “DV”? … --- ## [Calculating Simulation PK Parameters for 3 compartment model](https://forum.certara.com/t/calculating-simulation-pk-parameters-for-3-compartment-model/3643)
**Author:** [@emily](https://forum.certara.com/u/emily)\ **Replies:** 3\ **Last updated:** [October 24, 2022, 6:08am UTC](https://forum.certara.com/t/calculating-simulation-pk-parameters-for-3-compartment-model/3643 "2022-10-24T06:08:34Z")
Dear all, Our drug was administered by constant rate IV infusion in dose 72mg/m^2, Q4W and would like to konw the simulation profile and PK parameters change with 36mg/m^2, Q2W dosing regimen, especiallly for two analyt… --- ## [Error: Some data that is expected to be numeric is not](https://forum.certara.com/t/error-some-data-that-is-expected-to-be-numeric-is-not/3642)
**Author:** [@gew8](https://forum.certara.com/u/gew8)\ **Replies:** 3\ **Last updated:** [October 11, 2022, 6:05am UTC](https://forum.certara.com/t/error-some-data-that-is-expected-to-be-numeric-is-not/3642 "2022-10-11T06:05:33Z")
Hi all, I am getting the following error when I try to run a simple PK model. Can anyone advise? project attached. Im wondering if there is an issue with my input data set? Could not merge sort times Some data that is… --- ## [Testing diagonal covariance matrix](https://forum.certara.com/t/testing-diagonal-covariance-matrix/3638)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 2\ **Last updated:** [October 6, 2022, 3:40pm UTC](https://forum.certara.com/t/testing-diagonal-covariance-matrix/3638 "2022-10-06T15:40:09Z")
I have a question regarding testing diagonal covariance matrix (Full and partial block) in a model. Should we do it after adding the covariate effect into the final model, or before the stepwise process (base model)? Th… --- ## [How are theta tab CI calculated?](https://forum.certara.com/t/how-are-theta-tab-ci-calculated/3639)
**Author:** [@enixon](https://forum.certara.com/u/enixon)\ **Replies:** 2\ **Last updated:** [October 4, 2022, 1:03pm UTC](https://forum.certara.com/t/how-are-theta-tab-ci-calculated/3639 "2022-10-04T13:03:02Z")
Hi, I’ve written up the results of some modeling work and I have been asked to add how the parameter estimate CI are calculated. We expected it would be 1.96xSE, but that doesn’t appear to be the case. I cannot find the… --- ## [high correlation between variance terms and shared approach](https://forum.certara.com/t/high-correlation-between-variance-terms-and-shared-approach/3634)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 6\ **Last updated:** [October 1, 2022, 2:04am UTC](https://forum.certara.com/t/high-correlation-between-variance-terms-and-shared-approach/3634 "2022-10-01T02:04:41Z")
Hi, I have a question on addressing the high correlation between variance terms with (r-value is above 0.9). Trying an alternative parametrization approach could fix this issue (shared. approach). I am attaching a part … --- ## [PK Model With Dissolution and Bioavailability](https://forum.certara.com/t/pk-model-with-dissolution-and-bioavailability/3635)
**Author:** [@littlepetinga](https://forum.certara.com/u/littlepetinga)\ **Replies:** 5\ **Last updated:** [September 22, 2022, 3:12pm UTC](https://forum.certara.com/t/pk-model-with-dissolution-and-bioavailability/3635 "2022-09-22T15:12:29Z")
Hello everyone I am constructing a PK model which is preceded by a dissolution model (a Weibull model) in the GI track. From the dissolved drug in the GI, I pretend that only a fraction (F) is absorbed to the central co… --- ## [Modelling with IF()](https://forum.certara.com/t/modelling-with-if/3631)
**Author:** [@littlepetinga](https://forum.certara.com/u/littlepetinga)\ **Replies:** 13\ **Last updated:** [September 22, 2022, 3:11pm UTC](https://forum.certara.com/t/modelling-with-if/3631 "2022-09-22T15:11:01Z")
Hello everyone, I am using a very simple custom model to fit some dissolution data. I plan to fit the data to two different equations: (1) when time\<3, Fdiss=kd\*(Time^n) (2) when time\>=3, Fdiss=A^(Time) I am using t… --- ## [Question of output for individual modelling result](https://forum.certara.com/t/question-of-output-for-individual-modelling-result/3633)
**Author:** [@emilyh](https://forum.certara.com/u/emilyh)\ **Replies:** 6\ **Last updated:** [August 11, 2022, 12:36pm UTC](https://forum.certara.com/t/question-of-output-for-individual-modelling-result/3633 "2022-08-11T12:36:50Z")
Dear all, I would like to confirm the following issue: How did the IWRES be calculated from the output data? Is the IWRES=(DV-predicted)/weight ? what is detail calculation information of LOESS regression includin… --- ## [Modelling Macro Constants](https://forum.certara.com/t/modelling-macro-constants/3628)
**Author:** [@littlepetinga](https://forum.certara.com/u/littlepetinga)\ **Replies:** 3\ **Last updated:** [August 1, 2022, 10:42pm UTC](https://forum.certara.com/t/modelling-macro-constants/3628 "2022-08-01T22:42:49Z")
Dear All I am fitting some PK data with Phoenix ML Modelling. I am fitting the data with micro constant, but I also need to retrieve macro constants. I selected WNL built-in model 11 (2cp micro xvas), but I can’t under… --- ## [PD response prediction with intial estimate](https://forum.certara.com/t/pd-response-prediction-with-intial-estimate/3627)
**Author:** [@ygsla](https://forum.certara.com/u/ygsla)\ **Replies:** 2\ **Last updated:** [July 29, 2022, 5:47am UTC](https://forum.certara.com/t/pd-response-prediction-with-intial-estimate/3627 "2022-07-29T05:47:16Z")
Hi All, Want to understand if we can predict PD response with available published PK-PD model initial estimate value. I have PK data and want to predict PD response using literatute established PK-PD model value. Than… --- ## [problem about predictive check](https://forum.certara.com/t/problem-about-predictive-check/3626)
**Author:** [@crystal](https://forum.certara.com/u/crystal)\ **Replies:** 3\ **Last updated:** [July 27, 2022, 5:45am UTC](https://forum.certara.com/t/problem-about-predictive-check/3626 "2022-07-27T05:45:24Z")
Dear all I have a problem about predictive check. I built a pop PK model, after I finished covariates stepwise, I copied the model and run it in “simple” run mode. Then I copied the final model and accepted all fixed an… --- ## [Additive error being bound to minimize the effect of the BLQ imputation](https://forum.certara.com/t/additive-error-being-bound-to-minimize-the-effect-of-the-blq-imputation/3615)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 6\ **Last updated:** [July 6, 2022, 7:44pm UTC](https://forum.certara.com/t/additive-error-being-bound-to-minimize-the-effect-of-the-blq-imputation/3615 "2022-07-06T19:44:33Z")
Hi, I am working on a model with LLOQ concentrations being imputed. I found the following in a published PopPk analysis: " Residual variability was assumed to have an additive and a proportional element, with the addit… --- ## [stepwise text](https://forum.certara.com/t/stepwise-text/3622)
**Author:** [@crystal](https://forum.certara.com/u/crystal)\ **Replies:** 4\ **Last updated:** [July 5, 2022, 8:39am UTC](https://forum.certara.com/t/stepwise-text/3622 "2022-07-05T08:39:43Z")
Dear all, I have a problem about the Stepwise run model. I built a POP PK model, after I finished covariates stepwise, everything seems to be good, but when I check the Results—TextOutput—Stepwise Text, it confuses me t… --- ## [Error in setting covariates](https://forum.certara.com/t/error-in-setting-covariates/3621)
**Author:** [@vetpharma](https://forum.certara.com/u/vetpharma)\ **Replies:** 2\ **Last updated:** [July 4, 2022, 10:53am UTC](https://forum.certara.com/t/error-in-setting-covariates/3621 "2022-07-04T10:53:03Z")
Hi, I am building a pop PK model for L-Dopa. After I mapped my covariates, I ran the model, but I I am receiving a strange error saying that covariate for subject are not set. It starts with first covariate for first su… --- ## [Fitting issue](https://forum.certara.com/t/fitting-issue/3617)
**Author:** [@davidq8](https://forum.certara.com/u/davidq8)\ **Replies:** 8\ **Last updated:** [June 28, 2022, 5:01pm UTC](https://forum.certara.com/t/fitting-issue/3617 "2022-06-28T17:01:29Z")
Hi, I am trying to fit data to a model, but the model doesn’t show a good prediction to a specific time point (5th plasma sample); I tried different structural and error models but still no improvements. I am attaching … --- ## [building virtual population](https://forum.certara.com/t/building-virtual-population/3620)
**Author:** [@madushadrack](https://forum.certara.com/u/madushadrack)\ **Replies:** 3\ **Last updated:** [June 24, 2022, 1:10pm UTC](https://forum.certara.com/t/building-virtual-population/3620 "2022-06-24T13:10:09Z")
How do I go about building virtual population. for example weight with respect to age and height --- ## [How to count on SS for L-Dopa](https://forum.certara.com/t/how-to-count-on-ss-for-l-dopa/3619)
**Author:** [@vetpharma](https://forum.certara.com/u/vetpharma)\ **Replies:** 2\ **Last updated:** [June 23, 2022, 4:51pm UTC](https://forum.certara.com/t/how-to-count-on-ss-for-l-dopa/3619 "2022-06-23T16:51:30Z")
Hi, I am modeling the L-Dopa Cp-time profile following po administration of Sinemet. The dosing interval is q3h from morning to evening. In this study, blood samples were taken on day 14. The Cp-time profile, model and … [Previous page](https://forum.certara.com/c/phoenix/certara-forums/modelling-and-simulation/27.md?page=1) [Next page](https://forum.certara.com/c/phoenix/certara-forums/modelling-and-simulation/27.md?page=3)