help with modelling of categorical response data

Dear nmusers, I am planning to analyze categorical PD data from rats in order to make predictions for an effective concentration in humans. As I have never analyzed this type of data, I was hoping to get some help from some of the more experienced modellers. I have PK data available after intravenous drug administration as well as after administration of four different oral or s.c. doses, respectively, from some animals but not all. The PK can be described with a two-compartment model. Concerning the PD data, I have three different categories: no response, partial response, full response, available for both the oral as well as the s.c. route. Thus, the PD data looks like this: PD category dose (mg/kg) full response (%) partial response (%) no response (%) 0.5 0 0 100 0.75 17 0 83 1 33 17 50 1.5 50 50 0 The percent value means how many animals of the whole group show the respective response. My question is if it is possible to obtain a pharmacodynamic parameter such as an IC50 value from this type of data or if the information is insufficient. If that is the case, what kind of information can I get from this type of data? Any suggestions, including NONMEM control streams and information about the dataset creation (anything special there?) would be highly appreciated. One equestion that came to my mind was also whether it would be possible to treat one category as continuous in the sense that clearly, with higher concentrations, a lot more animals showed the full response? If it is possible, how would I implement this? Thanks and best wishes Nele _________________________ Dr. Nele Plock Bayer Schering Pharma AG Drug Metabolism & Pharmacokinetics Development Pharmacokinetics Scientific Expert Development Pharmacokinetics D- 13342 Berlin Phone : +49-30-468 15146 Fax: +49-30-468 95146 [EMAIL PROTECTED] http://www.bayerscheringpharma.de Vorstand: Arthur J. Higgins, Vorsitzender | Werner Baumann, Andreas Busch, Ulrich Köstlin, Kemal Malik, Gunnar Riemann Vorsitzender des Aufsichtsrats: Werner Wenning Sitz der Gesellschaft: Berlin | Eintragung: Amtsgericht Charlottenburg 93 HRB 283