DEFDOSE/DEFOBS Required for Many Compartments?

Hi, I have a model with many compartments (42 different compartments are defined). It is currently setup this way to future-proof the dataset in case we want to combine analyses of many drugs (about 20 different drugs with central/peripheral compartments) and several endpoints. In the current model, I'm only fitting the PK of one drug, so only two of the compartments are enabled: compartments 39 and 42. After the IGNORE statement, the data is relatively small with 400 records between 16 subjects, and all the data are in compartment 39 (the central compartment for the current drug). CMT, EVID, and MDV (along with everything else) is correctly specified. When I run the model with CMT 39 defined by: COMP=(PKCENT) ; 39 central PK compartment (ug/mL) the model fails with the error "COMPARTMENT ASSOCIATED WITH THE PREDICTION IS OFF" noted for all the dosing rows, but when I specify that compartment 39 is the default observation and dose compartment (due to IV dosing), the model works. COMP=(PKCENT,DEFOBS,DEFDOSE) ; 39 central PK compartment (ug/mL) I thought that when CMT and EVID are specified, DEFOBS and DEFDOSE are not important. Does anyone know why adding DEFOBS and DEFDOSE fixed my model? Thanks, Bill ------------------------------------------------------------------------ Human Predictions Logo < http://www.humanpredictions.com >*William S. Denney, PhD* Chief Scientist, Human Predictions LLC +1-617-899-8123 [email protected] This e-mail communication is confidential and is intended only for the individual(s) or entity named above and others who have been specifically authorized to receive it. If you are not the intended recipient, please do not read, copy, use or disclose the contents of this communication to others. Please notify the sender that you have received this e-mail in error by replying to the e-mail or by calling +1-617-899-8123. Please then delete the e-mail and any copies of it. Thank you.