Dose and concentration unit differences

From: "Gordi, Toufigh" Toufigh.Gordi@cvt.com Subject: [NMusers] Dose and concentration unit differences Date: Thu, 22 Sep 2005 14:56:10 -0700 Dear all, I am a little bit puzzled by an observation I have made when running a 2-comp PK model and would appreciate comments. I have a data file, where concentrations are given in ng/ml (which is the same as mcg/L). The dose was given as mcg. I use the log-normalized data. When I use the data as is, i.e. the data file contains the dose as mcg and the concentrations as ln(mcg/L) the model doesn't run and has problem. However, if I change the units and use ng for dose and ln(ng/L) for concentrations, i.e. simply multiply both by 1000, the model runs and gives quite acceptable results. Could anybody explain this? I give a couple of lines of the data file below: The data without any manipulations: #ID DATE=DROP TIME AMT (mcg) DV (ng/mL) EVID 4 5/15/2000 10:19 400 . 1 4 5/15/2000 10:25 . 15.9 0 4 5/15/2000 10:37 . 7.66 0 4 5/15/2000 11:04 . 4.28 0 4 5/15/2000 13:45 . 1.18 0 Dose in mcg, Conc. in ln (mcg/L). #ID DATE=DROP TIME AMT (mcg) DV (ng/mL) EVID 4 5/15/2000 10:19 400 . 1 4 5/15/2000 10:25 . 2.77 0 4 5/15/2000 10:37 . 2.04 0 4 5/15/2000 11:04 . 1.45 0 4 5/15/2000 13:45 . 0.17 0 Dose in ng, Conc. in ln(ng/L) #ID DATE=DROP TIME AMT (mcg) DV (ng/mL) EVID 4 5/15/2000 10:19 400000 . 1 4 5/15/2000 10:25 . 9.67 0 4 5/15/2000 10:37 . 8.94 0 4 5/15/2000 11:04 . 8.36 0 4 5/15/2000 13:45 . 7.07 0 Toufigh Gordi