Window of absorption

From: majid.vakily@tap.com Subject: [NMusers] Window of absorption Date: Mon, March 28, 2005 2:56 pm Hi, I am trying to do POPPK analysis for a drug with a window of absorption. The absorption from GI tract is initially slow and then there is a sudden increase in the plasma concentrations. Therefore, the absorption phase has two rate constants slow and rapid. I should also mention that the drug follows a compartment open model with a first order inputs and first order output processes. Is there a NONMEM subroutine for the window of absorption phenomenon?I have tried ADVAN 6 with differential equations. However, it is very slow. I appreciate any input about this issue and perhaps an example of control stream with statement for switching from the first absorption rate constant (Ka1, occurs earlier in profile and completed within 30 minutes) to the second absorption rate constant (Ka2, larger of two constants which may represent the optimal absorption site). Regards, Majid Vakily, Ph.D. Senior Research Investigator Department of Drug Metabolism & Pharmacokinetics Phone: (847) 582-2198 Fax; (847) 582-2388