Using administrative data to compare the relative effectiveness of amlodipine vs nifedipine CC.

Objective: To describe an approach for using claims data to compare the effectiveness of 2 similar drugs used for similar indications within a health maintenance organization. Study Design: A database study comparing the effectiveness of amlodipine and nifedipine CC in the initial treatment of hypertension. Patients and Methods: The claims records of Pennsylvania Medicaid patients between 18 and 64 years of age with continuous eligibility in 1994 were studied. Pharmacy, hospital, and outpatient claims data were merged, and adult patients receiving the target drugs for the specified indication were identified. The effectiveness of the 2 agents used were compared based on the concept that a change in dispensed medication suggested either an adverse event or lack of effectiveness. Adherence rates, adverse events, and pharmacy and nonpharmacy costs associated with the 2 agents were also compared. Results: Patients receiving amlodipine and nifedipine CC as initial treatment for hypertension had similar demographic characteristics and numbers of comorbid conditions. More patients started on nifedipine CC switched to another calcium channel blocker (15.8% for nifedipine CC vs 10.3% for amlodipine). More patients started on amlodipine switched to another class of antihypertensive agent From Health Services Research and Development, Veterans Affairs San Diego Healthcare System, and the University of California, San Diego, CA (LAL); Health Process Management, Doylestown, PA (WLZ, RN); and Bayer Corporation Pharmaceutical Division, Health Economics and Outcomes Research, West Haven, CT (BMK, JD, MES). This work was funded by Bayer Corporation, West Haven, CT. Address correspondence to: Leslie A. Lenert, MD, Health Services Research and Development, VA San Diego Healthcare System, 3350 La Jolla Village Drive (111N-1), San Diego, CA 92161. E-mail: llenert@ucsd.edu. In this cost-conscious healthcare environment, the clinical advantage of a newly approved agent must justify its purchase price. Examples of clinical advantages include greater efficacy, ease of use, fewer adverse events, and improved patient adherence. Importantly, efficacy findings from clinical trials data may not reflect effectiveness in real clinical practice. Differences in patient demographics, ethnic backgrounds, and other patient characteristics may influence the efficacy of a drug. Databases based on healthcare resource utilization records can help bridge this gap and provide (13.2% for amlodipine vs 7.3% for nifedipine CC). Patients in both groups received adjunctive antihypertensive drugs at a similar frequency (35% for nifedipine CC vs 42%, for amlodipine). Rates of adherence were similar. In adherent patients, there was no difference in rates of reported adverse events. The nonpharmacy costs were similar between groups. Patients in the amlodipine group also had a trend toward higher overall pharmacy charges (all medications) and higher charges for antihypertensive medications other than the study drugs ($302 vs $188, P=.054). Conclusions: Claims data are often the best available evidence for comparing the effectiveness of pharmaceuticals in real clinical practice. While these comparisons have inherent limitations, the accuracy of the assessment can be maximized by limiting the assessment to agents with the same specific indications. Other important elements include comparison of crossover rates to other pharmaceuticals in the same class, rates of addition of other pharmaceuticals in the same class, adherence, adverse events, and overall healthcare charges. (Am J Manag Care 1999;5:1535-1540) real-world information about the charges and clinical benefits of healthcare interventions. In this study, we used a retrospective database analysis to compare the effectiveness of 2 long-acting dihydropyridine calcium channel blockers, amlodipine and nifedipine CC, for the initial treatment of uncomplicated hypertension.