AUC calculations

Hello everyone, As a part of the simulations I was trying to perform using nonmem, I have a pkpd model. I have a Pharmacodynamic endpoint and was wondering if I could integrate the area under the curve of this endpoint for some time period, (say like AUC for this effect for last 24 hrs ) I guess i could do it in excel (or someone suggested me using SAS). Could I do this in NONMEM? any help would be appreciated. Thanks Navin