Hi Carlos, Adding to what the others suggested, please note that, if that EVID=0 record is the very first record for that patient, NONMEM will predict all compartments to be empty (all amounts = 0) at that time (unless you initialise as discussed below).
If indeed there were no doses before that sample and therefore the pre-dose sample is expected to contain no drug (it will come back as undetectable, or BLQ), then I think you should just use it as a check, but I would NOT fit that sample in the model, as it does not add much, and it is possibly a bit tricky to implement in NONMEM due to the 0 predictions. If, on the other hand, there were other doses before and the concentration in that sample could be (or maybe it's even expected to be) detectable, then you should fit that data point in the model. For that to happen, though, NONMEM needs to be able to predict something other than 0, in there, so you need to 1. either include in the dataset all the records for the previous doses (preferred if the dosing history is available) 2. or initialise the system to some value. For some ideas on approached for initialisation, you can have a look at the paper below. Dansirikul, C., Silber, H. E., & Karlsson, M. O. (2008). Approaches to handling pharmacodynamic baseline responses. Journal of Pharmacokinetics and Pharmacodynamics, 35(3), 269–283. https://doi.org/10.1007/s10928-008-9088-2 Good luck. Paolo On 2019/11/06 17:48, Carlos ST wrote: > Hi NMUsers community for you excellent suggestions. I will work through it. > Thanks, > > Carlos > > > > On Wed, 6 Nov 2019 at 15:12, Bill Denney <wden...@humanpredictions.com> wrote: >> Hi Carlos, >> >> It is commonly used. For most datasets, there will be at least one >> observation that occurs before dosing to estimate the baseline value, and in >> almost every scenario, the modeling dataset should mirror the real world >> actions. So, there is no issue with it, and usually you will have an EVID=0 >> before the first dose. >> >> Thanks, >> >> Bill >> >> -----Original Message----- >> From: owner-nmus...@globomaxnm.com <owner-nmus...@globomaxnm.com> On Behalf >> Of Carlos ST >> Sent: Wednesday, November 6, 2019 10:03 AM >> To: nmusers@globomaxnm.com >> Subject: [NMusers] Using evid 0 before dosing >> >> Dear NMUsers, >> >> I would like advice in the best practice to use evid 0 before dosing, which >> is to say an observation just before a dosing (*to estimate the value in >> that compartment just before dosing event). >> >> Thank you, >> >> Carlos, -- ------------------------------------------------ Paolo Denti, PhD A/Prof of Pharmacometrics Division of Clinical Pharmacology Department of Medicine University of Cape Town K45 Old Main Building Groote Schuur Hospital Observatory, Cape Town 7925 South Africa phone: +27 21 404 7719 fax: +27 021 650 5410 email: paolo.de...@uct.ac.za ------------------------------------------------ Disclaimer - University of Cape Town This email is subject to UCT policies and email disclaimer published on our website at http://www.uct.ac.za/main/email-disclaimer or obtainable from +27 21 650 9111. If this email is not related to the business of UCT, it is sent by the sender in an individual capacity. Please report security incidents or abuse via https://csirt.uct.ac.za/page/report-an-incident.php.
