Model estimates based on 1 sample per subject

From: tgordi@buffalo.edu Subject:[NMusers] Model estimates based on 1 sample per subject Date: 8/19/2003 2:48 PM Dear all, I have been asked by a friend to estimate the parameters of a simple binding study. Different infusion concentrations were administered to rats and 1 single sample was collected at 30 seconds after the start of he infusion (rats were sacrificed at this time point). There are several "dose" levels in the study. The data was first analysed using Winnonlin and Km, Bmax (maximum binding), and base line were estimated. The estimates look reasonable and in line with previous studies. I tried the same model (simple Hill equation) in NONMEM, running the model first in FOCE and then FO mode. The parameter estimates are very off from the expected range, not even close to the more reasonable Winnonlin estimates. I started with different initial values and the model has problems in getting to the same final estimates. Could the nature of the data, i.e. single sample per subject, explain the poor performance of the run? Is there any remedy for this? regards, Toufigh Gordi