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Modelling the economic impact of managing a chronic anal fissure with a proprietary formulation of nitroglycerin (Rectogesic) compared to lateral internal sphincterotomy in the United Kingdom |
Christie A, Guest J 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 nitroglycerin (0.2% glycerine nitrate, GTN) (Rectogesic) for the treatment of chronic anal fissure.
Economic study type Cost-effectiveness analysis.
Study population The study population comprised a hypothetical patient with chronic anal fissure.
Setting The setting was not stated, but it was likely to have been secondary care. The economic study was carried out in the UK.
Dates to which data relate The effectiveness data were gathered from studies published between 1995 and 2000. No dates for the resource use data were reported. The costs were expressed in 1999/2000 values.
Source of effectiveness data The effectiveness evidence was derived from completed studies and experts' assumptions.
Modelling A deterministic decision tree model was constructed on the basis of experts' opinions to describe the treatment patterns of patients with chronic anal fissure. The tree comprised the initial treatment (either 0.2% GTN or LIS), subsequent treatments for unsuccessfully healed fissures, subsequent treatments following symptomatic relapses, probabilities of outcomes and treatments, and time to successful healing following the initial treatment. Resource use data were associated with each path of the model, which was presented in full in the article. The time horizon of the model was not reported, but it appears to have lasted for at least 2 years as a long-term analysis was performed.
Outcomes assessed in the review The health outcomes assessed from the published studies were the following probabilities:
successful treatment with GTN or LIS,
partial faecal incontinence after LIS,
relapse following surgery,
healing after a second course of GTN,
botulinum infection, and
healing using botulinum.
Study designs and other criteria for inclusion in the review It was unclear whether a formal review of the literature had been undertaken. Some of the primary studies were randomised controlled trials, but the details of the studies were unclear.
Sources searched to identify primary studies Criteria used to ensure the validity of primary studies Methods used to judge relevance and validity, and for extracting data Number of primary studies included The effectiveness data were derived from 12 primary studies.
Methods of combining primary studies Investigation of differences between primary studies Results of the review The probabilities were:
65% for successful treatment with GTN,
96% for successful treatment with LIS,
9% for partial faecal incontinence after LIS,
3% for relapse following surgery,
83% for healing after a second course of GTN,
8% would be expected to have a botulinum infection, and
62% for healing using botulinum.
Methods used to derive estimates of effectiveness A panel of 11 colorectal surgeons and 4 general practitioners from across the UK was contacted to supplement published data on the treatment patterns and care provided to patients with chronic anal fissures. Most of the assumptions concerned resource use.
Estimates of effectiveness and key assumptions The probability of undergoing a second surgical procedure following a relapse after LIS was assumed to have been 30%. Twelve per cent of patients successfully treated with botulinum were assumed to relapse in the short term.
Measure of benefits used in the economic analysis The outcome of the decision model was the long-term probability of successful treatment. This was used as the summary benefit measure in the economic analysis.
Direct costs A 6% discount rate was applied to the costs incurred from the second year. The unit costs were not presented separately from the quantities of resources used. The health services included in the economic analysis were GTN, LIS, tests, conservative treatment, co-medications, and visits to the colorectal surgeon, general practitioner, nurse and physiotherapist. The cost/resource boundary was that of the NHS. The resource use data were estimated on the basis of experts' opinions. The unit costs were estimated from national published data such as the Department of Health, Personal Social Services Research Unit, or other studies. All of the costs were expressed in 1999/2000 values.
Statistical analysis of costs The costs were treated deterministically and were presented as point estimates.
Indirect Costs The indirect costs were not considered.
Sensitivity analysis One-way sensitivity analyses were performed on all model inputs (probability values, resource use data and unit costs) to estimate the robustness of the estimated costs. No justification was provided for the ranges used. A break-even analysis was also carried out for some parameters.
Estimated benefits used in the economic analysis The long-term probability of successful treatment was 99% with GTN and 100% with LIS. Therefore, the two procedures were considered to be equivalent.
Cost results The estimated (discounted) long-term costs were 615.92 with GTN and 840.26 with LIS.
The undiscounted figures were only slightly highly due to the fact that most of the costs were incurred in the short term.
The main cost driver was the acquisition costs of GTN in the GTN group (32.7%) and the cost of surgery in the LIS group (56%).
The expected NHS costs for GTN would be below 400 in 41% of cases, and between 800 and 1,200 in 30% of patients. However, for LIS, the expected NHS costs would be between 400 and 800 in 94% of cases, and only 6% of all cases would cost more than 1,200.
The sensitivity analysis showed that the estimated costs were strongly affected by the probability of successful treatment with GTN, the number of colorectal surgeon visits associated with GTN treatment, and the acquisition cost of GTN. The other model inputs had negligible effects on the expected costs.
Synthesis of costs and benefits A synthesis of the costs and benefits was not carried out because the two interventions were considered as equally effective. Therefore, the analysis was classified as a cost-minimisation analysis.
Authors' conclusions The use of glycerine nitrate (GTN) rather than lateral internal sphincterotomy (LIS) for the treatment of chronic anal fissure led to cost-savings in the long term, from the perspective of the National Health Service (NHS), while the two approaches provided comparable effectiveness.
CRD COMMENTARY - Selection of comparators The choice of the comparator, LSI, was appropriate because it represented the standard approach for patients with chronic anal fissures. The authors stated that alternative newer treatments (botulinum toxin or calcium antagonists) were available, but none of them was perceived as a sound comparator due to the high costs that limit widespread use (botulinum) or the lack of reliable evidence (calcium antagonists). You should decide whether LSI represents a valid comparator in your own setting.
Validity of estimate of measure of effectiveness The analysis of effectiveness was conducted using data coming from the literature and a panel of experts. However, it was not always clear which source had been used, and some published estimates were adjusted using experts' opinions. A systematic review of the literature was not performed and details of the primary studies, used to derive most of the effectiveness estimates, were not provided. Therefore, the quality of the sources used was unclear. In addition, the authors noted that most of the experts had a specific interest in using GTN. Thus, their estimations could have been biased and might not reflect the preferences of other surgeons with less interest in the treatment of anal fissures. Only some of the estimates derived from the expert panel were varied in the sensitivity analysis. These issues tend to limit the internal validity of the analysis.
Validity of estimate of measure of benefit The summary benefit measure used in the analysis was derived from the decision model. It was not combined with the costs in a cost-effectiveness ratio as, in effect, a cost-minimisation analysis was conducted. However, the benefit measure reflected a clinical end point and differences in patient preferences or quality of life issues were not considered. This could have been helpful as the study interventions had a substantial impact on the patients' well-being.
Validity of estimate of costs The perspective used in the analysis of costs was clearly stated. It appears that all the relevant categories of costs have been considered. A breakdown of the items was provided, although details on the unit costs and resources used were not reported. This limits the possibility of replicating the study in other settings. The costs were estimated from standard national sources, which were appropriate as NHS expenses were considered. The resource use data came from the expert panel. The authors carried out extensive sensitivity analyses to estimate the impact of variations in such data on the expected costs. This enhanced the robustness of the conclusions of the analysis. The price year was reported and an appropriate discount rate was used.
Other issues The authors compared their findings with those from other studies. Although few published studies were found, it appears that results consistent with those of the current economic evaluation have been observed, mainly in relation to the cost-savings associated with the use of GTN over LIS. The issue of the generalisability of the study results to other settings was not addressed explicitly. However, the results of the sensitivity analyses were reported very clearly, which increases the external validity of the analysis. The authors discussed some limitations of the analysis. In particular, the wide use of experts' opinion due to the lack of published data and the exclusion of indirect, intangible and non-medical costs.
Implications of the study The study results suggest that the use of GTN reduced health care costs associated with the long-term treatment of chronic anal fissures, without altering the effectiveness of the intervention. GTN therefore has the potential to be considered as a first-line treatment.
Source of funding Supported by Cellegy Pharmaceuticals Inc. (manufacturer of Rectogesic).
Bibliographic details Christie A, Guest J F. Modelling the economic impact of managing a chronic anal fissure with a proprietary formulation of nitroglycerin (Rectogesic) compared to lateral internal sphincterotomy in the United Kingdom. International Journal of Colorectal Disease 2002; 17(4): 259-267 Indexing Status Subject indexing assigned by NLM MeSH Anal Canal /surgery; Cost Control; Decision Trees; Fissure in Ano /economics /therapy; Great Britain; Health Care Costs /statistics & Health Resources /utilization; Humans; Models, Economic; Nitroglycerin /economics /therapeutic use; State Medicine /economics; Vasodilator Agents /economics /therapeutic use; numerical data AccessionNumber 22002001209 Date bibliographic record published 30/06/2004 Date abstract record published 30/06/2004 |
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