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

Study Objective. To evaluate the effectiveness, safety, and costs associate d with a formulary conversion from amlodipine to alternative calcium channe l blockers. Design. Retrospective study. Setting. Veterans Affairs Medical Center. Patients. One hundred patients with hypertension who were receiving amlodip ine. Intervention. Data from a random sample of 100 patients who were taking aml odipine and converted to a formulary calcium channel blocker from February 1, 1999-October 30, 1999, were entered into an Excel database for evaluatio n of the conversion. Measurements and Main Results. Patients were required to have a diagnosis o f hypertension and have had two consecutive clinic visits with blood pressu re measurements land no changes in antihypertensive therapy) before convers ion. 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 c alcium channel blocker, number of additional antihypertensives begun or dis continued, and number of dosage changes in antihypertensives within the two visits after conversion, and the overall cost impact of conversion. Averag e 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 sign ificantly reduced from 74 +/- 9.5 to 72.6 +/- 10.1 mm Hg after conversion ( p=0.032), as was MAP (97.0 +/- 9.3 to 94.8 +/- 10.0 mm Hg, p=0.026). Five p atients had other changes in therapy made concurrently at the time of conve rsion, and 19 had changes after conversion. When these patients were exclud ed 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 patien ts who had postconversion changes in therapy, 8 (42%) were converted to dil tiazem ER, nifedipine CC, or doses of felodipine that were 50% of the origi nal 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 re sulted in statistically significant reductions in diastolic blood pressure and MAP, and was safe as well as cost-effective. Conversion to calcium chan nel antagonists other than felodipine or less than equal dosages of felodip ine may require dosage titration. When converting patients from amlodipine, dosages usually should be equal to those of felodipine; if converting to o ther calcium channel antagonists, the need for adjustments should be antici pated.