BQL simulations

Hello everyone I have a simple question for a simple bicompartmental model where M3 method for estimating bql is used, because of that my predictions are overly inflated at the tail end of the treatment period (bql levels), which distorts my simulations. I used this line to get corrected predictions: IF(COMACT.EQ.1) PREDI=IPRED But that doesn't improve my simulated data at low concentrations, is there a way around it or should I use an other method to handle my bql values? Thank you in advance