CLIMCAL THERAPEUTICSVVOL. 17, NO. 6, 1995 Cost-Effectiveness Profiles with an Expanding Treatment Population zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM Paul C. Langley, PhD Center for Pharmaceutical Economics, College of Pharmacy, The University of Arizona, Tucson, Arizona ABSTRACT In trying to identify the therapeutic impact of a drug, clinical trials eliminate poten- tially confounding factors such as comor- bidities, poor compliance and treatment errors in diagnosis, dosing, and drug in- teractions. Elimination of these variables means that attempts to use clinical data as the basis for predicting relative cost-effec- tiveness are fraught with difficulties. In this article a theoretical framework is pro- posed, which, for a single drug interven- tion, examines the relationship between assumed patterns of clinical effectiveness, costs of drug delivery, and the proportion of the prospective patient population be- ing treated. Cost-effectiveness profiles are generated to represent both usual-treat- ment situations and situations where inter- ventions to reduce misdiagnoses, adverse events, and noncompliance attempt to push clinical effectiveness to a maximum (given the existence of comorbidities). Without data describing effectiveness and cost pro- files, and unless strict assamptions are made as to effectiveness and cost func- tions, profiles of cost-effectiveness cannot be predicted. INTRODUCTION Clinical trial results are of limited use as a predictor of a drug’s therapeutic impact in a real-world treating environment. Through their design, these trials elimi- nate patient characteristics such as comor- bidities and poor compliance that may af- fect measured clinical impacts and claims based on them. In addition, clinical trial results do not reflect treating environments where patients may be misdiagnosed or given inappropriate drug dosages or where the treating physician may fail to recog- zyxwv 0149-2918/95/$3.50 1207