Re: Initial conditions for amounts in compartments

From: Nick Holford <n.holford@auckland.ac.nz> Subject: Re: Initial conditions for amounts in compartments Date: Thu, 14 Sep 2000 06:43:29 +1200 Mike, You have run across one of the strange idiosyncrasies of the PREDPP library in NONMEM. Because PREDPP was designed to "do pharmacokinetics" the DE solving component is built to only allow setting of initial conditions by the AMT data item. The work around is simple although tedious because it involves modifying the data set. You will need to supply a CMT data item in addition to AMT. At the start of each individual set of data records insert a record with TIME=0, CMT=3 and AMT=1. At the times of doses into the CENTRAL compartment you should set CMT=1. PREDPP will then initialize the ENZIM compartment to 1. A further trick is required if you wish to estimate the initial amount in such a compartment. You can do this by estimating the bioavailability into that compartment e.g. F3=THETA(x) where F3 is the bioavailability into compartment 3. F3 is a special name known to PREDPP. There are no inbuilt constraints on F3 (except perhaps it must be non-negative) so you can estimate initial conditions that are > 1. Nick -- Nick Holford, Dept Pharmacology & Clinical Pharmacology University of Auckland, Private Bag 92019, Auckland, New Zealand email:n.holford@auckland.ac.nz tel:+64(9)373-7599x6730 fax:373-7556 http://www.phm.auckland.ac.nz/Staff/NHolford/nholford.htm