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 eff ectiveness of 2 similar drugs used for similar indications within a health maintenance organization. Study Design: A database study comparing the effectiveness of amlodipine an d 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 stu died. Pharmacy, hospital, and outpatient claims data were merged, and adult patients receiving the target drugs for the specified indication were iden tified. The effectiveness of the 2 agents used were compared based on the c oncept that a change in dispensed medication suggested either an adverse ev ent 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 treatme nt for hypertension had similar demographic characteristics and numbers of comorbid conditions. More patients started on nifedipine CC switched to ano ther calcium channel blocker (15.8% for nifedipine CC vs 10.3% for amlodipi ne). More patients started on amlodipine switched to another class of antih ypertensive agent (13.2% for amlodipine vs 7.3% for nifedipine CC). Patient s in both groups received adjunctive antihypertensive drugs at a similar fr equency (35% for nifedipine CC vs 42%, for amlodipine). Rates of adherence were similar. In adherent patients, there was no difference in rates of rep orted adverse events. The nonpharmacy costs were similar between groups. Pa tients in the amlodipine group also had a trend toward higher overall pharm acy charges (all medications) and higher charges for antihypertensive medic ations of her 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 thes e comparisons have inherent limitations, the accuracy of the assessment can be maximized by limiting the assessment to agents with the same specific i ndications. Other important elements include comparison of crossover rates to other pharmaceuticals in the same class, rates of addition of other phar maceuticals in the same class, adherence, adverse events, and overall healt hcare charges.