The effect of new and continuing prescription drug use on cost: A longitudinal analysis of chronic and seasonal utilization

Abstract

To provide basic information about 2 factors contributing to rising prescription drug costs--utilization trends and product selection. Prescription drug costs have risen sharply in recent years, and continued growth is expected. There is little consensus about appropriate cost-management strategies, in part because quantitative data on the causes and implications of increased drug costs are lacking. This study followed 463,820 continuously enrolled adult (> or = 18 years of age on January 1, 1996) utilizers of 15 chronic or seasonal therapeutic classes for 2.5 years (January 1996 through June 1998) using a pharmacy benefit manager's multiple-payer claims database. Outcome measures included (1) change in utilization rate, (2) relationship between new use and utilization growth, (3) stability of the treated population (ie, mostly long-term use vs high rates of turnover), and (4) product mix changes (ie, cost per dispensed day for 1996 vs 1997 and for new vs continuing users, controlling for inflation). Of the 463,820 utilizers, 97% were commercially insured and 3% enrolled in Medicare risk plans; 40% were enrolled in managed care and the remainder covered by indemnity insurance. Rates of growth and turnover varied substantially by class. The highest 2-year utilization rate change was 66.7% for antihyperlipidemic agents; change was < 10% in only 3 classes. Across classes, an average of 38.7% of 1997 users were new (ie, no use in 1996) and an average of 34.0% of 1996 users were dropouts (ie, no use in 1997). Utilization growth depended heavily on treatment continuation; classes with high dropout rates (eg, antirheumatic, antiasthmatic) did not have high growth rates, even with high rates of new use. In most classes, costs were not higher for new than for continuing users. In some classes, however (eg, antipsychotic, antidiabetic), both new and continuing users increased their use of newer, more expensive products. Because factors underlying rising prescription drug costs vary by therapeutic class, cost-containment strategies should address these differences. Further research is needed to assess the clinical and economic costs and benefits of rapid growth in the utilization of certain therapeutic classes.