Patterns of antihypertensive use among patients in the US Department of Defense database initially prescribed an angiotensin-converting enzyme inhibitor or calcium channel blocker

Abstract

The US Department of Defense recently assembled electronic records of outpatient prescriptions dispensed through the Uniformed Services Prescription Database Project (USPDP) going back to 1990. The objectives of this portion of a larger study were: (1) to examine longitudinally the patterns of antihypertensive drug use during the first year of therapy in patients whose initial therapy was with an angiotensin-converting enzyme (ACE) inhibitor or a calcium channel blocker (CCB); (2) to determine continuous and noncontinuous users of antihypertensive drugs; and (3) to estimate the direct medication costs for each pattern of medication use. Filtering criteria for patient and prescription identification were developed, because the USPDP contains no records of confirmatory diagnoses of hypertension. Once data filters were implemented, information for 771 patients was analyzed. An ACE inhibitor was the initial therapy for 328 patients, accounting for 1935 antihypertensive medication prescription fills, and a CCB was the initial therapy for 443 patients, accounting for 2459 fills (including refills). Slightly more than half of the patients (n = 401, 52.0%) were classified as continuous users (≥80% medication-possession ratio [supply of medication in days divided by the number of days in the 12-month study period]). In the first year, 177 of these continuous users (44.1%) had no change in therapy in the first year, 49 (12.2%) had an increase in dose, 8 (2.0%) had a decrease in dose, 15 (3.7%) had a change to a different therapeutic class of antihypertensive medication, 14 (3.5%) were changed to a different medication in the same therapeutic class, 20 (5.0%) had a new medication added to the regimen, and 118 (29.4%) had complex regimens involving more than one change. For continuous users, the mean medication supply in days was 354.6, and the average time before a medication change was 152.1 days for those continuous users who had one change in therapy. The overall average wholesale price (AWP) and average manufacturer price (AMP) for continuous users during 1 year of therapy were $471.31 and $378.51, respectively. For those patients whose therapy was changed to an ACE inhibitor/CCB combination and who were continuous users, the average AWP was $598.47 per year ($492.05 AMP). Once the change from monotherapy to an ACE inhibitor/CCB combination occurred in continuous users, AWP costs per member per month increased by approximately $22.00 ($18.00 AMP). Over half of the patients whose initial therapy was an ACE inhibitor or CCB had at least one change in their first year of therapy. Research into the reasons for these changes and their outcomes is needed.