Retrospective evaluation of the conversion of amlodipine to alternative calcium channel blockers.

STUDY
OBJECTIVE: To evaluate the effectiveness, safety, and costs associated with a formulary conversion from amlodipine to alternative calcium channel blockers.
DESIGN: Retrospective study.
SETTING: Veterans Affairs Medical Center. PATIENTS: One hundred patients with hypertension who were receiving amlodipine. INTERVENTION: Data from a random sample of 100 patients who were taking amlodipine and converted to a formulary calcium channel blocker from February 1, 1999-October 30, 1999, were entered into an Excel database for evaluation of the conversion.
MEASUREMENTS AND MAIN RESULTS: Patients were required to have a diagnosis of hypertension and have had two consecutive clinic visits with blood pressure measurements (and no changes in antihypertensive therapy) before conversion. End points were changes in average systolic blood pressure, diastolic blood pressure, and mean arterial pressure (MAP) from the two clinic visits before and after conversion. In addition, data were collected and analyzed with regard to adverse drug reactions, average dosage of the alternative calcium channel blocker, number of additional antihypertensives begun or discontinued, and number of dosage changes in antihypertensives within the two visits after conversion, and the overall cost impact of conversion. Average systolic blood pressure was reduced from 141.6 +/- 15.1 to 139.2 +/- 15.3 mm Hg after the conversion (NS). Average diastolic blood pressure was significantly reduced from 74 +/- 9.5 to 72.6 +/- 10.1 mm Hg after conversion (p=0.032), as was MAP (97.0 +/-q 9.3 to 94.8 +/- 10.0 mm Hg, p=0.026). Five patients had other changes in therapy made concurrently at the time of conversion, and 19 had changes after conversion. When these patients were excluded from analysis, the reduction in systolic blood pressure after conversion was significant (141.4 +/- 14.5 to 137.7 +/- 14.3 mm Hg, p=0.022), as were reductions in diastolic blood pressure (74.4 +/- 9.4 to 71.7 +/- 9.8 mm Hg, p=0.014) and MAP (96.7 +/- 9.1 to 93.7 +/- 9.3 mm Hg, p=0.007). Of patients who had postconversion changes in therapy, 8 (42%) were converted to diltiazem ER, nifedipine CC, or doses of felodipine that were 50% of the original dose of amlodipine. The overall cost impact of the conversion was a net savings of $14,858/year for each 100 patients converted.
CONCLUSION: Conversion from amlodipine to other calcium channel blockers resulted in statistically significant reductions in diastolic blood pressure and MAP, and was safe as well as cost-effective. Conversion to calcium channel antagonists other than felodipine or less than equal dosages of felodipine may require dosage titration. When converting patients from amlodipine, dosages usually should be equal to those of felodipine; if converting to other calcium channel antagonists, the need for adjustments should be anticipated.