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


METHODS
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.
Divisions of Hematology/Oncology, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109-0429, USA.
Darren
D
Kocs
A Mark
AM
Fendrick
D000046:Academic Medical Centers; D000911:Antibodies, Monoclonal / Q000009:adverse effects / Q000191:economics / Q000627:therapeutic use*; D058846:Antibodies, Monoclonal, Murine-Derived; D000970:Antineoplastic Agents / Q000009:adverse effects / Q000191:economics / Q000627:therapeutic use*; D002173:Cancer Care Facilities; D017277:Drug Approval; D016527:Drug Costs; D004348:Drug Labeling; D017723:Drug Utilization Review; D004513:Education, Pharmacy, Continuing; D005260:Female; D006302:Health Services Research; D017721:Hospital Costs; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000145:classification / Q000188:drug therapy*; D012189:Retrospective Studies; D000069283:Rituximab; D014481:United States
D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D000970:Antineoplastic Agents; D000069283:Rituximab