Poor PRED estimates

From: "Justin Wilkins" Subject: [NMusers] Poor PRED estimates Date: Thu, 22 May 2003 18:16:11 +0200 Hi all, I'm working on a model for rifampicin in healthy volunteers, using ADVAN4, and I'm having a great deal of trouble getting credible population predictions - while the population DVs often go as high as 25-30 ug/mL, population predictions never go above 15 ug/mL, giving a truncated, cone-shaped DV vs PRED plot that suggests something exponential is wrong. IPRED values seem all right though. The data is rich - 300 individuals sampled at least 8 times on each occasion, and each subject being sampled on at least 2 occasions - and I've been able to get rough parameter estimates from a noncompartmental analysis of the information. I only have plasma data for V2, which means one wouldn't expect much joy from V3 or Q, but I strongly suspect a two-compartment model is appropriate, especially since ADVAN2 PRED results are extremely poor. Being a relative NONMEM neophyte, I'm stumped. Does anyone have any advice? Control stream follows. Thanks in advance! Justin