PD of drugs in combination therapy

Hi I was wondering if anyone has experience modeling the effect of three separate drugs on the same biomarker. In my area of research in organ transplantation, patients often take three immunosuppressive agents concomitantly, all of which will contribute toward a PD marker (i.e. reduction of intracellularly expressed IL-2 in mitogen stimulated lymphocytes). Most published work on drug combinations, however, deal with agonistic or antagonistic activity of two drugs as summarized by Jonker et al, 2005. All suggestions or advice are greatly appreciated. Fatemeh Fatemeh Akhlaghi, PharmD, PhD Associate Professor in Pharmacokinetics Biomedical and Pharmaceutical Sciences (BPS) University of Rhode Island 125 Fogarty Hall, 41 Lower College Road Kingston, RI 02881, USA Phone/Fax: (401) 874 9205/(401) 874 2181 Email: fatemeh Laboratory Website: http://www.uri.edu/pharmacy/faculty/aps/akhlaghi