AN EQUILIBRIUM-MODEL OF DRUG UTILIZATION

We propose an equilibrium model to assess the dispensing pattern of non-steroidal anti-inflammatory drugs (NSAIDs) among members of a health maintenance organization. The model incorporates observed patterns of patient switching among NSAIDs and identifies an implicit equilibrium distribution of drug dispensing, which may be used both to identify aberrations in prescription practice and to forecast the expected utilization of newly introduced drugs. NSAID dispensing patterns were stable for most quarters from 1987 to 1990. Introduction of two new NSAIDs and initiation of a pharmacy co-payment coincided with transient perturbation of the patterns. Dispensings of recently introduced NSAIDs achieved their equilibrium values in less than 2