DDEs in NONMEM

Dear all, I have a problem regarding delay differential equations (DDEs) in NONMEM. So far, I have been unable to find a way of successfully using DDEs in NONMEM, due to there being no in-built DDE solver (as far as I know). To me, it seems that the problem is that there is no way of recalling the value of the dependant variable at an earlier time point within the $DES block (u(t-T), where T is some fixed value, possibly to be estimated). I think that the problem is not a simple one to solve as NONMEM uses an adaptive step size when performing the integration, so even if there was a table output of the past values of the dependant variable, the value at the exact time (u(t-T)) might not exist. Has anybody been able to successfully implement DDEs in NONMEM? I would really appreciate some help with this. Note: I am talking about DDEs in a general sense, I know that certain specific cases of DDEs can be solved in NONMEM (ref: Modelling of delays in PKPD, classical approaches and a tutorial for delay differential equations, G Koch, W. Krzyzanski, J. J. Perez-Ruixo, Johannes schropp, JPKPD). Many thanks, Jon Moss, PhD Modeller BAST Inc Limited Loughborough Innovation Centre Charnwood Wing Holywell Park Ashby Road Loughborough, LE11 3AQ, UK Tel: +44 (0)1509 222908