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A comparative analysis of amlodipine and felodipine in a military outpatient population: efficacy, outcomes, and cost considerations |
Blivin S J, Pippins J, Annis L G, Lyons F |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology The use of amlodipine (AML) and felodipine (FEL), two dihydropyridine calcium-channel blockers, for the treatment of hypertension.
Economic study type Cost-effectiveness analysis.
Study population The study population consisted of patients who needed antihypertensive therapy and required a calcium-channel blocker such as ALM or FEL.
Setting The setting was a military hospital. The economic study was carried out at the Naval Hospital in Jacksonville (FL), USA.
Dates to which data relate The effectiveness and resource use data were gathered between January and March 1999. The price year was not explicitly stated, but it is likely to have been 1999.
Source of effectiveness data The effectiveness data were derived from a single study.
Link between effectiveness and cost data The costing was carried out retrospectively on the same patient sample as that used in the effectiveness analysis.
Study sample Power calculations, if performed, were not reported. The patients were randomly selected from all the charts available at the study institution, that is, more than 4,000 patients who had received AML and approximately 100 to 150 patients who had received FEL during the 3-month study period. The final sample comprised 42 patients who had received the study drugs for at least 6 months as outpatients at the authors' institution and had three pre-therapy and three post-therapy blood pressure (BP) measurements available. There were 30 patients in the AML group and 12 in the FEL group. The mean age was 55.7 years in the AML group and 60.5 years in the FEL group. The proportion of males was 50% in the AML group and 58% in the FEL group.
Study design This was a retrospective cohort study, which was carried out in a single centre. The method used for assigning the patients to the study groups (i.e. patient or physician preferences) was not described. The length of follow-up, which was derived from hospital records, was not reported clearly, although the authors provided the mean duration of antihypertensive therapy. All of the patients were available for follow-up assessment because only charts with complete records were selected.
Analysis of effectiveness All of the patients included in the initial study sample were considered in the effectiveness analysis. The primary health outcome was the proportion of patients who reached BP control. This was defined according to published guidelines as a systolic BP of less than 140 mmHg and a diastolic BP of less than 90 mmHg. The mean of three BP measurements before drug therapy and the mean of three BP measurements after drug therapy were taken. The secondary outcome measures were average drug dose, duration of antihypertensive therapy, use of concomitant antihypertensive drugs and adverse events. The study groups were shown to have been comparable at baseline in age, gender, co-morbidities and concomitant diagnoses.
Effectiveness results The proportion of patients achieving BP control was 87% (13% in the pre-drug period) in the AML group and 33% (25% in the pre-drug period) in the FEL group, (p<0.001).
The systolic BP changed from 157.5 (+/- 20.9) to 132.1 (+/- 10.5) mmHg (difference: -25.4 +/- 21.4) in the AML group, and from 148.5 (+/- 16.1) to 144.2 (+/- 17.2) mmHg (difference: -4.2 +/- 18.6) in the FEL group.
The diastolic BP changed from 91 (+/- 12.8) to 77.4 (+/- 9.1) mmHg (difference: -13.5 +/- 12.2) in the AML group, and from 81.8 (+/- 11.7 to 79.5 (+/- 11.3) mmHg (difference: -2.3 +/- 13.6) in the FEL group.
The average drug dose was 5.7 mg for AML and 7.8 mg for FEL.
The mean duration of antihypertensive therapy was 26 months for AML and 11 months for FEL, (p=0.00047).
Before drug therapy, 72% of AML patients and 67% of FEL patients were taking concomitant cardiovascular medication. After treatment, the use of concomitant antihypertensive drugs decreased to 60% for patients in the AML group, but increased to 75% for patients in the FEL group. However, the change in the total number of concomitant medications was not statistically significantly different between the groups, -0.2 (+/- 0.5) in AML patients versus 0.17 (+/- 0.6) in FEL patients, (p=0.06).
None of the AML patients reported any side effects, but 2 patients in the FEL group experienced headache, (p=0.076 versus AML patients), and 4 reported peripheral oedema, (p=0.004 versus AML).
Clinical conclusions The analysis of effectiveness showed that AML was more effective than FEL in achieving BP control. No side effects were observed with AML.
Measure of benefits used in the economic analysis The summary benefit measure used in the economic analysis was the efficacy rate, that is, the proportion of patients achieving BP control. This measure was derived directly from the effectiveness study.
Direct costs Discounting was not relevant and was not carried out because of the short time horizon of the analysis. The unit costs were not presented separately from the quantities of resource use. The categories of costs considered in the analysis were AML, FEL and other cardiovascular medications. The perspective of the study was that of the federal health authority. The drug prices were obtained from the federal health authority, while the resource use data were derived from the sample of patients included in the effectiveness study. The price year was not reported, but it is likely to have been 1999.
Statistical analysis of costs Statistical tests of the costs were not carried out.
Indirect Costs The indirect costs were not included.
Sensitivity analysis Sensitivity analyses were not conducted.
Estimated benefits used in the economic analysis See the 'Effectiveness Results' section.
Cost results The total daily medication costs were $0.756 in AML patients and $0.598 in FEL patients.
Synthesis of costs and benefits The average cost per patient with BP control was $0.87/day with AML and $1.79/day with FEL. An incremental cost-effectiveness analysis was not carried out.
Authors' conclusions Despite the initial acquisition costs, amlodipine (AML) treatment was cost-effective in comparison with felodipine (FEL) due to the higher proportion of patients achieving BP control. The annual savings for the military institution where the study was conducted would be about $1.3 million.
CRD COMMENTARY - Selection of comparators The authors did not provide any justification for the choice of the comparators as other calcium-channel blockers or other antihypertensive therapies were available. You should decide whether they represent valid comparators in your own setting.
Validity of estimate of measure of effectiveness The effectiveness study used a retrospective cohort study, but the use of a prospective and randomised trial would have been more appropriate. The patient data were retrieved from hospital charts, but for some outcome measures (e.g. length of follow-up) the information contained in the charts was not clearly available. The main limitation to the internal validity of the analysis was the small sample size and the fact that power calculations were not conducted. The two groups were comparable at baseline and the effectiveness analysis considered all the patients included in the study sample.
Validity of estimate of measure of benefit The benefit measure was derived from the effectiveness study (see commentary above). However, the measure was disease-specific and is difficult to compare with the benefits of other health care interventions.
Validity of estimate of costs The authors stated the perspective adopted in the study and provided a breakdown of the costs. Only the drug costs were included in the analysis and other items, such as outpatient visits or monitoring services, were not considered. The authors did not explain their choice of the categories of costs considered. Details of the unit costs, quantities of resources used and the price year were not reported. This could represent a limitation to the transferability of the results to other settings. The cost estimates were specific to the study settings and sensitivity analyses were not performed. No statistical tests of the costs were conducted.
Other issues The authors compared their findings with those from other studies and similar results were observed. However, the issue of the generalisability of the study results to other settings was not addressed. This resulted in a low external validity of the analysis. The authors calculated an average cost-effectiveness ratio, but an incremental analysis would have been more appropriate.
Implications of the study The authors noted some implications of their study. First, the information on the drug acquisition cost may be misleading when the total costs of treatment are evaluated. Second, the study institution has kept AML in the formulary, but has removed FEL due to the results of the study. Third, additional prospective analyses should be conducted to corroborate the findings of the present study.
Bibliographic details Blivin S J, Pippins J, Annis L G, Lyons F. A comparative analysis of amlodipine and felodipine in a military outpatient population: efficacy, outcomes, and cost considerations. Military Medicine 2003; 168(7): 530-535 Other publications of related interest Burt VL, Whelton P, Roccella EJ, et al. Prevalence of hypertension in the U.S. adult population: results from the Third National Health and Nutrition Examination Survey, 1988-1991. Hypertension 1995;25:305-13.
Oatis G, Stowers AD. A formulary conversion from amlodipine to felodipine ER: did the change fulfil expectations? Formulary 2000;35:432-42.
Indexing Status Subject indexing assigned by NLM MeSH Amlodipine /economics /pharmacology /therapeutic use; Analysis of Variance; Antihypertensive Agents /economics /pharmacology /therapeutic use; Blood Pressure /drug effects; Calcium Channel Blockers /economics /pharmacology /therapeutic use; Cost Control; Drug Costs /statistics & Felodipine /economics /pharmacology /therapeutic use; Female; Florida; Hospitals, Military; Humans; Hypertension /drug therapy; Male; Medical Audit; Middle Aged; Military Personnel /statistics & Naval Medicine /economics /methods; Retrospective Studies; Statistics, Nonparametric; Treatment Outcome; numerical data; numerical data AccessionNumber 22003009751 Date bibliographic record published 31/05/2004 Date abstract record published 31/05/2004 |
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