Total asthma-related costs for patients taking inhaled corticosteroids were significantly lower than those for patients taking leukotriene modifiers (P<.05). Patients taking inhaled corticosteroids also incurred decreased annual total (allcause) medical care costs. Although this difference was qualitatively large (approximately $1900, or a decrease of over 17%), it did not reach statistical significance.
Pre- vs post-initiation of therapy
In addition to comparing the impact of the 2 therapies on resource use and costs, we were interested in the impact of initiating each therapy on the study outcomes. We therefore assessed resource use rates and costs before and after treatment initiation. These patients may have been receiving asthma therapies (or no asthma therapy) other than inhaled corticosteroids or leukotriene modifiers. The number of studies presenting data on costs was too small to allow comparison.
Results of this within-group analysis are presented in Table 3. For patients taking inhaled corticosteroids, hospitalization rates and emergency department visit rates decreased significantly after treatment initiation compared with the preinitiation values (P<.005 and P<.05, respectively). The decreases for patients taking leukotriene modifiers upon treatment initiation were smaller and not statistically significant.
Both groups showed similar small decreases in annual emergency department costs, neither of which was significant. The increases in annual total drug costs and annual total medical care costs after treatment initiation were significant for both groups of patients (all at P<.005). However, both increases were greater for patients taking leukotriene modifiers; the increase in drug costs was statistically significant (P<.001).
TABLE 3
Resource utilization and costs before and after therapy initiation for inhaled corticosteroids vs leukotriene modifiers*
| Before vs after treatment, mean (95% confidence interval) | |||
|---|---|---|---|
| Inhaled corticosteroid patients | Leukotriene modifier patients | Absolute difference | |
| Annual hospitalization rate | -2.37%† (-2.89 to -1.86) | -0.55% (-1.18 to 0.08) | -1.91%‡(-2.45 to -1.36) |
| Annual rate of visits to the emergency department due to asthma | -4.44%§ (-5.98 to -2.90) | -2.06% (-3.61 to -0.51) | -2.47%||(-3.09 to -1.86) |
| Total annual costs of the emergency despartment | -$5 (-21 to 10) | -$15 (-44 to 15) | $9 (-33 to 51) |
| Total annual drug costs | $415†(312-517) | $579† (472-686) | -$167||(-192 to 142) |
| Total annual medical care costs | $641† (113-1169) | $1712† (927-3529) | -$1080 (-2802 to 643) |
| *Post-therapy initiation values for inhaled corticosteroids and leukotriene modifiers are presented in Table 1. | |||
| †Before vs after treatment initiation significant at P<.005. | |||
| ‡Before vs after treatment initiation outcomes for inhaled corticosteroids vs leukotriene modifiers significant at P<.01. | |||
| §Before vs after treatment initiation significant at P<.05. | |||
| ||Before vs after treatment initiation outcomes for inhaled corticosteroids vs leukotriene modifiers significant at P<.001. | |||
Discussion
In this study, we used meta-analysis to combine data across studies and determine more robust estimates of the impact of inhaled corticosteroid vs leukotriene modifier therapy on medical resource use rates and costs. The primary analysis indicated that annual hospitalization rates among patients taking inhaled corticosteroids are significantly lower that those taking leukotriene modifiers. Other resource use rates and costs evaluated in this study also generally showed decreased values for patients taking inhaled corticosteroids.
Although meta-analysis generally has been used for clinical outcome measures, it is a highly appropriate method for resource use and cost outcomes. In general, studies of the impact of a particular treatment are powered to assess safety and efficacy or effectiveness; there is often insufficient power to detect differences in resource use or costs in any one study. Due to substantial variation in treatment patterns, the variance associated with resource use rates (and associated costs) may be substantially higher than that for clinical measures; such a wide variance adds to the difficulties in assessing differences for nonclinical outcomes.
Limitations
This study has a number of limitations. Only a few studies met inclusion criteria for the meta-analysis; the analysis should be replicated as additional studies become available. Data were abstracted from the included studies without modification (except for inflating costs to 2000 values when necessary). As in all meta-analyses, any problems present in the original data are present in the combined data; limitations of the original data are not addressed by this method.
Among the studies evaluated for the metaanalysis were a number published only as abstracts. Inclusion of unpublished literature in meta-analyses is controversial; however, several sources18,19 now recommend inclusion of published and unpublished studies. Egger and Smith26 found that studies with significant results are more likely to be published than are studies with nonsignificant results, leading to publication bias. Studies with significant results also may be more likely to be published in indexed journals, leading to “database bias.” As such, inclusion of unpublished studies is important to produce unbiased results.
Five of the 6 studies that met the inclusion criteria were observational, retrospective cohort analyses. Whereas many meta-analyses focus solely on prospective, randomized clinical trials, several have included retrospective data.27,28 Retrospective analyses and observational data have a number of limitations, in particular the lack of randomization that can lead to differences in characteristics of specified treatment groups. Further, as discussed by Egger et al,29 metaanalyses based on observational studies may involve bias and confounding.