RE: Two sequential absorption processes

Hello, I think that the model that you refer to is called the KOKA absorption model (Holford et al. J Pharmacokinet Biopharm. 1992; 20:421-42). You don't need $DES, it can be easily coded using ADVAN4 (it will greatly reduce your run time). I guess you know what fraction of the dose enters as a zero order process and what remaining fraction enters as the first order process (I see that you have KO in the code). The fraction that enters as the zero order process is the THETA(2) in the code below. Moreover, you will need 2 dosing records per dose that enters the system, see example dataset for 1 individual below as well. In my experience, the duration of the zero order input and its corresponding fraction was unknown. You can even estimate these parameters. The only trick is that if you estimate the fraction, please put THETA(2) inside a logit function [you can find more details here: Samtani MN, Vermeulen A, Stuyckens, K. Population pharmacokinetics of intramuscular paliperidone palmitate in patients with schizophrenia. A novel once-monthly, long-acting formulation of an atypical antipsychotic. Clin Pharmacokinet. 48: 585-600 (2009)] Good luck, Mahesh _______________________________________________________________________________________________ $PK CALLFL=-2 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; KA TVKA=THETA(1) KA =TVKA*EXP(ETA(1)) ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ALAG & DN DUR = 2.99 D2 = DUR ALAG1 = DUR ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; FN TVF=THETA(2) ; replace THETA(2) with your known fraction. F2 = TVF F1 = 1-TVF #ID TIME DV CMT AMT RATE 6001 0 0 1 10 0 6001 0 0 2 10 -2 6001 1 0.2 2 0 0 6001 6 1.9 2 0 0 6001 24 0.1 2 0 0