Effect of off-label use of oncology drugs on pharmaceutical costs: the rituximab experience

Abstract

Background: While the off-label use of oncology interventions is widespread, the factors influencing off-label use and the resultant influence on oncology drug expenditures are not well understood.

Study design: To assess the indications for rituximab use, a retrospective review was undertaken at a single academic center between September 1998 and June 2001.

Methods: Patient diagnoses were linked to pharmacy records, and each administration of rituximab was classified as either on-label or off-label as defined by FDA-approved indications. The resultant utilization patterns were the foundation for a conceptual model designed to identify factors that influence off-label use of oncology-related therapeutics and forecast the effect of off-label use on aggregate oncology drug expenditures.

Results: One hundred one patients received a total of 428 rituximab administrations during the study period. Most (320, 75%) of the administrations were for off-label indications. Although the extent of off-label and on-label use grew at a similar rate initially, off-label utilization increased nearly exponentially over time as on-label uses lessened. A conceptual model that describes factors that promote, inhibit, or have a mixed influence on off-label use may help predict future patterns of off-label utilization and allow better forecasting of oncology drug expenditures.

Conclusions: The off-label use of rituximab is substantial. Projections of oncology-related patterns of care and drug expenditures must account for the potential for off-label use.