Generating EQ-5D-5L health utility scores from BASDAI and BASFI: a mapping study in patients with axial spondyloarthritis using longitudinal UK registry data

BACKGROUND

Preference-based health-state utility values (HSUVs), such as the EuroQol five-dimensional questionnaire (EQ-5D-5L), are needed to calculate quality-adjusted life-years (QALYs) for cost-effectiveness analyses. However, these are rarely used in clinical trials of interventions in axial spondyloarthritis (axSpA). In these cases, mapping can be used to predict HSUVs.

OBJECTIVE

To develop mapping algorithms to estimate EQ-5D-5L HSUVs from the Bath Ankylosing Disease Activity Index (BASDAI) and the Bath Ankylosing Spondylitis Functional Index (BASFI).

METHODS

Data from the British Society for Rheumatology Biologics Register in Ankylosing Spondylitis (BSRBR-AS) provided 5122 observations with complete BASDAI, BASFI, and EQ-5D-5L responses covering the full range of disease severity. We compared direct mapping using adjusted limited dependent variable mixture models (ALDVMMs) and optional inclusion of the gap between full health and the next feasible value with indirect response mapping using ordered probit (OPROBIT) and generalised ordered probit (GOPROBIT) models. Explanatory variables included BASDAI, BASFI, and age. Metrics to assess model goodness-of-fit and performance/accuracy included Akaike and Bayesian information criteria (AIC/BIC), mean absolute error (MAE) and root mean square error (RMSE), plotting predictive vs. observed estimates across the range of BASDAI/BASFI and comparing simulated data with the original data set for the preferred/best model.

RESULTS

Overall, the ALDVMM models that did not formally include the gap between full health and the next feasible value outperformed those that did. The four-component mixture models (with squared terms included) performed better than the three-component models. Response mapping using GOPROBIT (no squared terms included) or OPROBIT (with squared terms included) offered the next best performing models after the three-component ALDVMM (with squared terms). Simulated data of the preferred model (ALDVMM with four-components) did not significantly underestimate uncertainty across most of the range of EQ-5D-5L values, however the proportion of data at full health was underrepresented, likely due in part to model fitting on a small number of observations at this point in the actual data (4%).

CONCLUSIONS

The mapping algorithms developed in this study enabled the generation of EQ-5D-5L utilities from BASDAI/BASFI. The indirect mapping equations reported for the EQ-5D-5L facilitate the calculation of the EQ-5D-5L utility scores using other UK and country-specific value sets.

Cost-Effectiveness of Treatment Strategies with Biologics in Accordance with Treatment Guidelines for Ankylosing Spondylitis: A Patient-Level Model

BACKGROUND

Ankylosing spondylitis (AS) is a form of rheumatic disease caused by chronic inflammation of the axial skeleton. Patients with AS experience significant functional limitations and reduced quality of life. Consequently, AS imposes a substantial economic burden on society due to productivity loss and work disability. Biologics, including tumor necrosis factor (TNF) inhibitors and human anti-interleukin-17A monoclonal antibody (IL-17A) agents, are effective treatment strategies in relieving symptoms and slowing down disease progression. Currently, 5 TNF inhibitors and 2 IL-17A antibody agents are approved by the FDA for the management of AS. Of these agents, there is no clear preferred agent in initial biologic therapy, although an IL-17A antibody agent or alternative TNF inhibitor agent is recommended after failure of the initial TNF inhibitor therapy.

OBJECTIVE

To assess cost-effectiveness of treatment strategies with biologics, TNF inhibitor or IL-17A, in accordance with the treatment guidelines for patients with AS.

METHODS

An economic patient-level simulation combining decision-tree and Markov models was constructed from the U.S. health care payer's perspective over a 10-year time horizon. The current model examined 5 treatment strategies: (1) conventional care treatment with nonsteroidal anti-inflammatory drugs, (2) 1 TNF inhibitor, (3) an IL-17A antibody agent, (4) sequential therapy with 2 TNF inhibitors, and (5) sequential therapy with a TNF inhibitor followed by an IL-17A antibody agent. Initially, treatment responses were determined after 12-week treatments. Patients who responded to treatment entered a "responders" Markov model. Patients entered a "nonresponders" Markov model if they inadequately responded to treatment. In sequential treatment strategies, patients who inadequately responded to treatment with the first TNF inhibitor received a second TNF inhibitor or an IL-17A antibody agent. Health utility was estimated based on the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Functional Index (BASFI) scores. The models accounted for real-world adherence to TNF inhibitor treatment. Scenario and probabilistic sensitivity analyses were performed to test the robustness and uncertainty of the model results.

RESULTS

Over a 10-year time horizon and 100,000 simulated patients for each treatment strategy, base-case results produced average total discounted per-patient costs of $19,765, $130,302, $159,934, $190,553, and $179,118 and quality-adjusted life-years (QALYs) of 4.675, 5.410, 5.499, 5.919, and 5.893 for conventional care, treatment strategies with 1 TNF inhibitor, an IL-17A, 2 TNF inhibitors, and a TNF inhibitor followed by an IL-17A, respectively. The optimal treatments at willingness-to-pay (WTP) thresholds ≤ $130,813 per QALY, between $130,813 per QALY and $442,728 per QALY, and > $442,728 per QALY were conventional care and sequential treatment strategies with 1 TNF inhibitor, followed by an IL-17A agent and 2 TNF inhibitors, respectively.

CONCLUSIONS

Study findings suggested that all treatment strategies with biologics, TNF inhibitors or IL-17A antibody agents, in the treatment guidelines for AS were not cost-effective at the common WTP of $100,000 per QALY. However, the sequential treatment with 1 TNF inhibitor followed by an IL-17A antibody agent was considered cost-effective at a higher WTP of $150,000 per QALY.

DISCLOSURES

No outside funding supported this study. The authors have nothing to disclose. Primary findings of this study were presented in part at the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) in Baltimore, MD, May 2018.

Modeling Health State Utility Values in Ankylosing Spondylitis: Comparisons of Direct and Indirect Methods

OBJECTIVES

Cost-effectiveness analyses of technologies for patients with ankylosing spondylitis frequently require estimates of health utilities as a function of the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and the Bath Ankylosing Spondylitis Functional Index (BASFI).

METHODS

Linear regression, bespoke mixture models, and generalized ordered probit models were used to model the EuroQol five-dimensional questionnaire as a function of BASDAI and BASFI. Data were drawn from a large UK cohort study (n = 516 with up to five observations) spanning the full range of disease severity.

RESULTS

Linear regression was systematically biased. Three- and four-component mixture models and generalized probit models exhibit no such bias and improved fit to the data. The mean, median, mean error, and mean absolute error favored the mixture model approach. Root mean square error favored the generalized ordered probit model approach for the data as a whole. Model fit assessed using these same measures by disease severity quartiles tended to be best using the mixture models. The value of moving from good to poor health may differ substantially according to the chosen method. Simulated data from the mixture and probit models yield a very similar distribution to the original data set.

CONCLUSIONS

These results add to a body of evidence that the statistical model used to estimate health utilities matters. Linear models are not appropriate. The four-class bespoke mixture model approach provides the best performing method to estimate the EuroQol five-dimensional questionnaire values from BASDAI and BASFI.

Cost effectiveness of dipeptidyl peptidase-4 inhibitors for type 2 diabetes

BACKGROUND

Dipeptidyl peptidase-4 (DPP-4) inhibitors are a new class of antidiabetic drugs used for treating type 2 diabetes mellitus. While many studies have reported on the cost-effectiveness of DPP-4 inhibitors for treating type 2 diabetes, a systematic review of economic evaluations of DPP-4 inhibitors is currently lacking.

OBJECTIVES

The aim of this systematic review was to assess the cost effectiveness of DPP-4 inhibitors for patients with type 2 diabetes.

DATA SOURCES

MEDLINE, EMBASE, National Health Service Economic Evaluation Database (NHS EED), Web of Science, EconLit databases, and the Cochrane Library were searched in November 2013.

STUDY ELIGIBILITY CRITERIA, PARTICIPANTS AND INTERVENTIONS

Studies assessing the cost effectiveness of DPP-4 inhibitors for type 2 diabetes were eligible for analysis. DPP-4 inhibitor monotherapy or combinations with other antidiabetic agents were included in the review. The DPP-4 inhibitors were all marketed drugs. Two reviewers independently reviewed titles, abstracts, and articles sequentially to select studies for data abstraction based on the inclusion and exclusion criteria. Disagreements were resolved by consensus.

STUDY APPRAISAL AND SYNTHESIS METHODS

The quality of included studies was assessed according to the 24-item checklist of the Consolidated Health Economic Evaluation Reporting Standards (CHEERS) statement. The costs reported by the included studies were converted to US dollars via purchasing power parities (PPP) in the year 2013 using the CCEMG-EPPI-Center Cost Converter.

RESULTS

A total of 11 published studies were selected for inclusion; all were cost-utility analyses. Nine studies were conducted from a payer perspective and one used a societal perspective; however, the perspective of the other study was unclear. Four studies were of good quality, six were of moderate quality, and one was of low quality. Of the seven studies comparing DPP-4 inhibitors plus metformin with sulfonylureas plus metformin, six concluded that DPP-4 inhibitors were cost effective in patients with type 2 diabetes who were no longer adequately controlled by metformin monotherapy. Five studies compared DPP-4 inhibitors with thiazolidinediones, and whether DPP-4 inhibitors were cost effective was uncertain. Only two economic evaluations provided data to compare DPP-4 inhibitors versus insulin, and the results favored the use of DPP-4 inhibitors as second-line therapy.

LIMITATIONS

Synthesis of the data was impossible because of heterogeneity in the methodology and data sources of the economic evaluations, and the inclusion criteria excluded conference abstracts. It was difficult to find reliable weightings for each of the items of the CHEERS checklist, and the ratings were dichotomous.

CONCLUSIONS AND IMPLICATIONS OF KEY FINDINGS

This study provides the first systematic evaluation of DPP-4 inhibitors for patients with type 2 diabetes. It found that, in patients with type 2 diabetes who do not achieve glycemic targets with antidiabetic monotherapy, DPP-4 inhibitors as add-on treatment may represent a cost-effective option compared with sulfonylureas and insulin. However, high-quality cost-effectiveness analyses that utilize long-term follow-up data and have no conflicts of interest are still needed.

The cost-effectiveness of solifenacin vs. trospium in the treatment of patients with overactive bladder in the German National Health Service

OBJECTIVE

To carry out a cost-utility analysis comparing initial treatment of patients with overactive bladder (OAB) with solifenacin 5 mg/day versus either trospium 20 mg twice a day or trospium 60 mg/day from the perspective of the German National Health Service.

METHODS

A decision analytic model with a 3 month cycle was developed to follow a cohort of OAB patients treated with either solifenacin or trospium during a 1 year period. Costs and utilities were accumulated as patients transitioned through the four cycles in the model. Some of the solifenacin patients were titrated from 5 mg to 10 mg/day at 3 months. Utility values were obtained from the published literature and pad use was based on a US resource utilization study. Adherence rates for individual treatments were derived from a United Kingdom general practitioner database review. The change in the mean number of urgency urinary incontinence episodes/day from after 12 weeks was the main outcome measure. Baseline effectiveness values for solifenacin and trospium were calculated using the Poisson distribution. Patients who failed second-line therapy were referred to a specialist visit. Results were expressed in terms of incremental cost-utility ratios.

RESULTS

Total annual costs for solifenacin, trospium 20 mg and trospium 60 mg were €970.01, €860.05 and €875.05 respectively. Drug use represented 43%, 28% and 29% of total costs and pad use varied between 45% and 57%. Differences between cumulative utilities were small but favored solifenacin (0.6857 vs. 0.6802 to 0.6800). The baseline incremental cost-effectiveness ratio ranged from €16,657 to €19,893 per QALY.

LIMITATIONS

The difference in cumulative utility favoring solifenacin was small (0.0055-0.0057 QALYs). A small absolute change in the cumulative utilities can have a marked impact on the overall incremental cost-effectiveness ratios (ICERs) and care should be taken when interpreting the results.

CONCLUSION

Solifenacin would appear to be cost-effective with an ICER of no more than €20,000/QALY. However, small differences in utility between the alternatives means that the results are sensitive to adjustments in the values of the assigned utilities, effectiveness and discontinuation rates.

Cost effectiveness of therapeutic interventions in ankylosing spondylitis: a critical and systematic review

OBJECTIVES

This report reviews the cost effectiveness of different therapeutic interventions used in the treatment of ankylosing spondylitis (AS).

METHODS

We performed a systematic search of the databases MEDLINE via PubMed, EMBASE and the Cochrane Library and used hand-searching to identify articles on cost effectiveness of therapies for adult patients with AS published up to November 2010.

RESULTS

Of 135 articles, 13 studies were analysed. Two articles were on physical therapies, one article was on NSAIDs and ten articles were on tumour necrosis factor (TNF) inhibitors (infliximab = 6, etanercept = 2, infliximab and etanercept = 1 and adalimumab = 1). Of the latter, no article directly compared TNF inhibitors. Articles showed substantial heterogeneity in methodological approaches and thus results, which prevented us from any extensive comparison, data pooling or meta-analysis. The incremental cost-effectiveness ratio (ICER) for spa-exercise treatment was &U20AC;7465 (95% CI 3294, 14 686) per QALY. The ICERs for infliximab, etanercept and adalimumab were &U20AC;5307-237 010, &U20AC;29 815-123 761 and &U20AC;7344-33 303 per QALY, respectively.

CONCLUSIONS

Modelling treatment strategies in chronic relapsing diseases such as AS presents specific challenges, as reflected in the variation in the cost-effectiveness results reported. Although quite variable, the cost-effectiveness ratios for AS therapies remain within an acceptable range.

Cost-effectiveness of vaccinating adults with the 23-valent pneumococcal polysaccharide vaccine (PPV23) in Germany

The introduction of routine infant vaccination against pneumococcal disease has resulted in a decreased overall invasive pneumococcal disease incidence in adults but also a change in invasive pneumococcal disease serotypes. This study aimed to assess the cost-effectiveness of 23-valent pneumococcal polysaccharide vaccine (PPV23) in Germany in this context. A population-based Markov model was developed. A cohort of adults currently eligible for vaccination was followed until death. Adult vaccination with PPV23 was associated with an incremental cost-effectiveness ratio of €17,065/quality-adjusted life years gained from the third-party payer's perspective. Univariate sensitivity analyses showed that the incremental cost-effectiveness ratio was below €50,000/quality-adjusted life years gained in most test scenarios. The model suggests that adult PPV23 vaccination is cost effective in Germany, due to its broad serotype coverage. This is despite epidemiological changes in Streptococcus pneumoniae serotypes caused by wider use of pneumococcal conjugate vaccines during childhood.

Economic considerations of the treatment of ankylosing spondylitis

Ankylosing spondylitis (AS) is associated with both significant direct and indirect costs, which vary by country, and have generally increased dramatically since the introduction of anti-tumor necrosis factor therapy. The cost-effectiveness of biologic agents is controversial, although cost-effectiveness studies need to consider the potential impact of anti-tumor necrosis factor treatments on work ability. Alternatives to reduce costs associated with biologics have been examined, including on-demand dosing and lower dose alternatives. Other treatment measures, such as total hip arthroplasty and physical therapy, are also effective in reducing pain and improving function in patients with AS, although the optimal type or combination of physical therapy treatment modalities, the optimal frequency and duration of treatment and whether therapy is equally effective in stable disease and uncontrolled AS need to be determined. No studies have examined differences in patient outcomes based on subspecialty care. Establishing an evidence base for these questions would help inform policy decisions to design the most cost-effective measures to treat AS.