An analysis of the diffusion of new antidepressants: variety, quality, and marketing efforts.

BACKGROUND: We are not aware of any published research that quantifies and compares the importance of effectiveness and side effects for pharmaceutical sales, and that simultaneously incorporates the impacts of marketing efforts on the diffusion of new pharmaceutical agents in the U.S. The overall level and market share success of the various selective serotonin reuptake inhibitors ( SSRIs ) relative to a representative older generation tricyclic (such as amitriptyline) provides a useful focus for studying such issues. AIMS OF STUDY: To model jointly the marketing and sales relationships of the SSRIs in the U.S., to quantify the extent to which marketing efforts are responsive to the availability of new scientific information accompanying changes in quality and increases in product variety, and in turn to assess how the new FDA indication approvals and the enhanced marketing initiatives involving product quality and variety affect sales of the SSRI and other novel antidepressants.
METHODS: Quarterly US sales, price, quantity and marketing data 1988Q1-1997Q4 are taken from IMS Health for the eight new antidepressants introduced into the US during this time period. Measures of physician-perceived quality attributes of the antidepressants are drawn from Market Measures, Inc., a medical survey research firm. These data are used to construct measures of product quality (effectiveness and side effect profile), and attribute variety across all antidepressants. Multivariate regression methods are used in estimating parameters of a marketing efforts model, a sales demand model encompassing the aggregate of the newer antidepressants, and a product share model. Simulation methods are employed to quantify elasticities.
RESULTS: Since 1988, and relative to amitriptyline, there has been only a rather modest increase in the perceived average effectiveness of the SSRIs and related products, but the side effect profiles have improved substantially. Variety measures for effectiveness show greater increases over time than do those for side effects. Marketing efforts respond to science-based events, such as new FDA indication approvals, and to effectiveness and side-effect quality improvements. Total antidepressant sales are positively and significantly related to price reductions, increased marketing efforts, and the level and variety of side effect profiles involving antidepressants. The level and variety of effectiveness does not significantly affect total antidepressant sales. Order of entry effects are important in affecting product market shares, while marketing efforts and relative quality attributes (particularly a more favorable side effect profile) have positive and significant impacts on relative market shares. IMPLICATIONS FOR HEALTH CARE PROVISION AND USE: Since patient response to SSRIs and related products is idiosyncratic, greater product variety facilitates better matching of antidepressant with patient. Much of the growth of the SSRIs and related antidepressants since 1988 can be attributed to increased product attribute variety, to improved changes in side effect quality relative to that of the tricyclics, and to the marketing of those improvements. IMPLICATIONS FOR HEALTH POLICIES: Marketing efforts play an important role in diffusing product information. Marketing efforts increase considerably following FDA approval for indications other than depression, and also increase with the average effectiveness and the average side effect rating of the products. IMPLICATIONS FOR FURTHER RESEARCH: Whether the relatively minor role that perceived effectiveness has in affecting sales relative to perceived side effect profile is unique to antidepressants, or generalizes to other therapeutic classes, merits further examination.