A Cost Analysis of Switching Calcium Channel Blockers: RESULTS

In: Main

3 Jul 2010

Records Evaluated

A total of 372 randomly selected patient records were reviewed. Fifty-four of the patients whose records were selected were no longer receiving antihypertensive therapy, and they were excluded from the analysis. Four additional patients died during the follow-up period, and their records were also excluded. Thus, records from 314 patients form the basis for the results described in this section. The baseline demographic and clinical characteristics for these patients are summarized in Table 1. Despite the relatively restrictive criteria for maintaining patients on amlodipine, there were not substantive differences between the demographic and clinical characteristics of patients who did and did not switch antihypertensive therapy. Overall, 78% of the patients (n=245) had hypertension and 22% (n=69) had hypertension and angina. Prior to the switch, 65.9% of patients were being treated with once daily, and the remaining patients were taking 10 mg/day. The mean amlodipine daily dose prior to conversion was 6.7 mg.

Table 1 Patient Characteristics at the Time of Formulary Conversion

All Patients Control Group* Conversion Group**
Number of patients 314 62 252
Men 153 (48.7%) 28 (45.2%) l25 (49.6%)
Women 161 (51.3%) 34 (54.8%) l27 (50.4%)
Mean age (years) 66.6 66.8 66.5
Men: mean (range) 66.7 (40-90) 66.2 (46-84) 66.8 (40-90)
Women: mean (range) 66.5 (39-89) 67.4 (44-85) 66.2 (39-89)
Diagnosis
Hypertension only 245 (78%) 51 (82.3%) l94 (77%)
Hypertension + angina 69 (22%) 11 (l7.7%) 58 (23%)
*Patients remaining on amlodipine constituted the control group. **Patients converted to felodipine ER or nifedipine CC constituted the conversion group.

Current Therapy

Current therapy for the patients whose records were reviewed is summarized in Table 2. The average felodip-ine ER dose post-conversion was 7.9 mg/day and the dose for nifedipine CC was 55.5 mg/day. The average post-conversion dose of the patients who remained on amlodipine was 6.9 mg/day.

The average cost per day for amlodipine therapy prior to the switch was $0.67. Post-conversion, the average per-day cost for felodipine ER was $0.53 and the cost for nifedipine CC was $0.48. The daily cost for patients who remained on amlodipine canadian was $0.75.

Table 2 Comparison of Antihypertensive Therapy Before and After Conversion

DHP No. of Avg. Therapy Cost
Therapy Patients Dose (per day)
Initial Therapy
Amlodipine 314 6.7 mg/day $0.67
Post-conversion
Felodipine ER 190 7.9 mg/day $0.53
Nifedipine CC 53 55.5 mg/day $0.48
No DHP therapy 9 N/A N/A
Converted patients 252 N/A $0.52
Amlodipine 62 6.9 mg/day $0.75

Concomitant CV Medications

There was a substantial rise in the use of concomitant CV medications after the switch from amlodipine to either ER or nifedipine CC (Table 3). Overall, 52.2% of patients were taking at least one additional CV drug prior to the switch. After the switch, this value increased to 84.5%. In particular, there were increases in the use of ACE-inhibitors, a-blockers, angiotensin receptor blockers, p-blockers, diuretics, and nitrates. The use of additional CV medications fell to 43.5% in the patients maintained on amlodipine. The switch in therapy also resulted in an increase in doses for all CV medications, except for sublingual nitro-glycerin and nitroglycerin patches (Table 4).

Table 3 Concomitant Cardiovascular (CV) Medications

Before Switching After Switching
Drug No. of Patients Dose*

No. of Patients

Dose*
 

29

53.4

48

66.1

 

20

25.0

48

28.6

9

35.6

34

40.0

 

19

38.9

37

45.4

 

22

17.9

65

24.8

27

18.5

36

25.6

 

21

90.5

37

113.5

Nitroglycerin
Patch

5

10.0

12

10.0

 

33

0.4

44

0.4

Cost Analysis

The costs for dihydropyridines (DHPs) and other CV drugs are summarized in Table 5. The results show that the switch had the intended effect of reducing acquisition costs for DHPs, but the unintended result of increasing the overall cost for CV medications. Switching significantly reduced the mean daily cost of DHPs from $0.67 to $0.56 (P<0.001). However, it significantly increased the mean daily cost for concomitant CV medications from $0.08 to $0.30 (P<0.001) and the mean total cost for all CV medications, including DHPs, from $0.75 to $0.86 per day (P<0.001).

Table 5 Mean Daily Per-Patient Costs for Cardiovascular (CV) Drugs (All Patients)*

Drug Initial Therapy Current
Therapy (Amlodipine) Therapy

Significance

DHPs $0.67 ±0.13 $0.56 ± 0.31

P<0.001

Concomitant
CV medications $0.08 ±0.15 $0.30 ± 0.37

P<0.001

All CV
medications $0.75 ± 0.20 $0.86 ± 0.49

P<0.001

Additional analyses indicated the same outcome as above when the results for patients maintained on amlodipine were compared with those from patients switched to either canadian felodipine ER or nifedipine CC. The mean daily DHP costs, the costs for concomitant CV drugs, and the total CV drug costs for patients maintained on amlodipine were $0.75 ± 0.56, $0.07 ± 0.18, and $0.82 ± 0.58, respectively; the corresponding values for the patients switched from amlodipine were $0.52 ± 0.17, $0.36 ± 0.38, and $0.88 ± 0.42.

The between-group differences in DHP and concomitant CV medication costs were both statistically significant (P=0.0007 and P<0.0001, respectively).

A calculation of the total monthly costs for the 314 patients whose records were included in the analysis indicated that the overall cost of DHPs decreased from $6,311 to $5,275 as a result of the switch. The cost for concomitant CV medications increased from $754 to $2,826, and the total cost for all CV drugs increased from $7,065 to $8,101 (Figure 1). The average monthly per-patient cost for all CV drugs increased from $22.50 to $25.80 (14.7%). Importantly, this analysis includes patients maintained on amlodipine in the post-switch averages. The average monthly per-patient cost for all CV medications in the amlodipine group was $24.59, whereas the cost for the patients who changed antihyper-tensive therapies was $26.40.

Table 6 Numbers and Costs of Concomitant Cardio¬vascular (CV) Drugs for Hypertensive Patients (HTN) and Those With Hypertension and Angina Before and After Switching from Amlodipine

DHP         No. of On Concomitant     No. of     Cost/ Therapy     Patients   CV Drugs (%)   Drugs/Patient Day
Initial Therapy
Amlodipine
HTN

245

42.4 0.50

$0.05

HTN + angina

69

86.9 1.38

$0.18

Current Therapy
Felodipine ER
HTN

143

77.6 1.24

$0.21

HTN + angina

47

100 2.83

$0.78

Canadian Nifedipine CC
HTN

44

84.1 1.41

$0.28

HTN + angina

9

100 2.44

$0.52

No DHP
HTN

7

100 2.43

$0.73

HTN + angina

2

100 4.00

$0.92

Amlodipine
HTN

51

31.4 0.33

$0.03

HTN + angina

11

100 1.82

$0.23

Results for Patients with Hypertension Alone Versus Those for Patients with Hypertension Plus Angina

A review of the results in Table 4 suggests that a substantial portion of the increased use of concomitant CV medications after the switch from amlodipine was for additional drugs (e.g., isosorbide mononi-trate, nitroglycerin or possibly atenolol canadian, metoprolol) that were required for the control of angina symptoms. Therefore, it was important to assess the effects of the switch on patients with hypertension alone versus those with hypertension and angina. The results of this analysis are presented in Table 6. They show that the costs of concomitant CV drugs for patients switched to felodipine ER or nifedipine CC were higher than those prior to the switch. They also demonstrate that the cost of concomitant CV drugs for patients switched to felodip-ine ER or CC were higher than those for patients maintained on amlodipine. This applied to individuals with hypertension alone and to those with hypertension plus angina. For patients with hypertension, the average daily costs for concomitant CV drugs for individuals receiving amlodipine before and after the switch were $0.05 and $0.03, respectively. The respective values for hypertensive patients switched to felodipine ER and nifedipine CC were $0.21 and $0.28. For patients with hypertension plus angina, the average daily costs for concomitant CV drugs for individuals receiving amlodipine before and after the switch were $0.18 and $0.23, respectively. The corresponding values for the patients switched to felodipine ER and nifedipine CC were $0.78 and $0.52, respectively.


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