Cost effectiveness of early treatment with oral aciclovir in adult chickenpox Smith K J, Roberts M S

Transcription

1 Cost effectiveness of early treatment with oral aciclovir in adult chickenpox Smith K J, Roberts M S 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 limit first-lastutforal aciclovir for adult chickenpox. Type of intervention Treatment. Economic study type Cost-utility analysis. Study population Adult patients with chickenpox. The baseline analysis was conducted on patients aged 20 years, under the assumption that chickenpox severity and aciclovir effects did not change from that age onwards. Setting logo ""The setting was not stated directly, but was presumably in primary care. The study was carried out in Pennsylvania, USA. Dates to which data relate 1994 direct and indirect costs were used. The effectiveness data were taken from studies published from 1990 to The incidence of chickenpox related hospitalisations and deaths were taken from US general population statistics published in Source of effectiveness data The evidence for the effectiveness of oral aciclovir appears to have been taken from three studies. Modelling A decision-tree model in Decision Maker 7.0 was used to integrate estimates of outcome, utilities and costs, in order to estimate the cost-effectiveness of aciclovir. Outcomes assessed in the review The effect of aciclovir on the number of days of febrile illness and length of total illness was assessed. Study designs and other criteria for inclusion in the review Page: 1 / 5

2 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 Three primary studies were included. Methods of combining primary studies Investigation of differences between primary studies The differences between the studies were not investigated. Results of the review Baseline length of illness data were obtained from a single randomised controlled trial, although 2 other studies were also cited. This trial demonstrated a reduction in febrile illness by 0.5 days and length of total illness by 1.8 days resulting from oral aciclovir given within 24 hours of rash onset. It was assumed that there would be no treatmentrelated moderation of symptoms for days with fever (based on one study). Aciclovir was assumed not to reduce the rate or length of hospitalisation, or to lessen the mortality associated with chickenpox, although no references were provided. Measure of benefits used in the economic analysis The benefit from aciclovir was measured in terms of Quality Adjusted Life Years (QALYs) gained. A decision-tree model was used to estimate the effects of oral aciclovir versus no antiviral therapy. The utility values used were estimated from a number of sources. The utility value for days of chickenpox with fever was approximated from the Sackett and Torrance utility value for short term home confinement for an 'unnamed contagious disease'. Three apparently randomised controlled trials (RCTs) of aciclovir for chickenpox in addition to the Sackett and Torrance paper were used to estimate utility values for days without fever. The method of valuation was not stated. A further RCT of aciclovir for chickenpox, which was conducted in children, was also cited as a source of utility values in the text but not in the summary table. Direct costs Drug costs were estimated as the average wholesale price for a seven day course of aciclovir. Hospitalisation costs were estimated from disease-related group payments and physician reimbursement for pneumonia. The cost of an outpatient visit was estimated, but no data source was provided. No discounting was conducted on the basis that costs and benefits due to aciclovir therapy occurred only at the time of illness. The drug cost of aciclovir related to 1994, however dates for the other cost data were not provided. No reflation of costs was conducted. Statistical analysis of costs Page: 2 / 5

3 Indirect Costs The indirect costs for illness, hospitalisation, and death were derived from the average weekly wage for non-farm workers in the US in 1994, unadjusted for age, gender, race or employment status. The indirect cost of illness was calculated on a daily basis, with hospitalisation estimated at an average of two weeks' absence. The indirect costs of death were calculated as wages lost from the time of death to the age of 65 years (human capital approach). These estimates appear to have been guesses. No discounting or reflation of costs were performed. Currency US dollars ($). Sensitivity analysis All probabilities and utilities used in the model were varied using one-way sensitivity analyses. Direct costs were varied from 0 to 5 times their baseline values. Multivariate sensitivity analyses were performed on estimated efficacy, utility values and aciclovir costs. Multivariate sensitivity analyses were also conducted using chickenpox illness utilities and aciclovir illness assumptions which would be unfavourable to an aciclovir treatment strategy. Estimated benefits used in the economic analysis Using baseline assumptions, the treatment of adult chickenpox patients within 24 hours of rash onset produced additional QALYs (or 1.07 quality-adjusted life days) compared with symptomatic therapy only. Cost results The average total direct cost of the aciclovir strategy was $ compared to $ for the no antiviral therapy strategy. From the societal perspective, the total cost of the aciclovir strategy was $ compared to $ for the no antiviral therapy strategy. Therefore the incremental cost of aciclovir treatment from the third-party payer perspective was $ and from the societal perspective was $ (i.e. cost-saving). Synthesis of costs and benefits From the third-party payer perspective the incremental cost per QALY gained from aciclovir treatment was $42,900. From the societal perspective, aciclovir was found to be cost saving compared with no antiviral treatment and no costeffectiveness ratio was presented. From the third-party payer perspective the one-way sensitivity analyses showed the incremental cost-effectiveness of aciclovir to be sensitive to illness utility values, degree of symptomatic relief and shortening of illness provided by aciclovir. Variation of these parameters could increase the incremental cost-effectiveness ratio to over $50,000 per QALY gained. The model was also found to be sensitive to the assumption that aciclovir does not affect chickenpoxrelated hospitalisations or deaths. Under the assumption that aciclovir can reduce these outcomes, the incremental costeffectiveness ratio decreased significantly. There was no reporting of any sensitivity analysis of costs. From the societal perspective, the one-way sensitivity analyses found the model to be sensitive only to variations in aciclovir related shortening of illness, or to variation in medication costs. Changes in these variables made aciclovir costgenerating rather than cost-saving. If days of illness were shortened by less than 1.63 days but greater than 0.17 days (baseline value 1.8 days), the cost per QALYgained remained less than $50,000. Likewise, if medication costs were greater than $ but less than $282, the cost per QALY gained from aciclovir remained less than $50,000. Authors' conclusions The authors concluded that aciclovir for adult chickenpox is cost-effective and is probably cost saving when indirect costs of illness are considered. The cost-effectiveness ratio when only direct costs were considered ($42,000 per QALY), was shown to compare favourably with other accepted therapeutic interventions. Page: 3 / 5

4 CRD COMMENTARY - Selection of comparators The selection of comparators appears to be adequate, although there may be other treatments for chickenpox which were not discussed in the study. Validity of estimate of measure of benefits: The estimates of benefit produced by aciclovir were very poor. Three studies appear to have been used to estimate the efficacy of the treatment. No detail was provided regarding the retrieval or assessment of these studies (i.e. the literature search, inclusion/exclusion criteria, validity assessment or data extraction). No study details were provided. No rationale was provided as to why one particular study was relied upon more heavily than the others. It is impossible to assess whether the efficacy estimates are appropriate or generalisable. The estimates for health state utilities used in the model were derived from the literature for an 'unnamed contagious disease' rather than chickenpox and as such need to be treated with some caution. Validity of estimate of costs The economic study design was appropriate for the analysis under consideration, however the estimation of the costs used does not appear to have been valid. Direct hospitalisation costs were based on tariffs, which are not true reflections of actual costs and no data source was provided regarding the cost of an outpatient visit. Direct costs were varied from 0 to 5 times the baseline value in the sensitivity analysis yet no rationale for this was provided. Indirect costs were based only on an estimate of lost productivity and no attention was paid to other societal costs including patient costs or time spent caring for patients by their families. The indirect cost of illness was calculated on a daily basis, yet no baseline length of illness data were presented. The indirect cost of hospitalisation was based on an average of two weeks absence from work, but no basis for this assumption was provided. The indirect cost of death was calculated using the human capital approach but there is no discussion of the problems with using such an approach. No sensitivity analyses were conducted for indirect costs. Other issues The authors' conclusions regarding the cost-effectiveness of aciclovir were based on rather weak evidence given the problems with the estimates of both benefits and costs. In addition the model is highly sensitive to small changes in the variables suggesting that the estimated cost-effectiveness ratios are not very reliable. Source of funding None stated. Bibliographic details Smith K J, Roberts M S. Cost effectiveness of early treatment with oral aciclovir in adult chickenpox. PharmacoEconomics 1998; 13(5 Part 2): PubMedID Indexing Status Subject indexing assigned by NLM MeSH Acyclovir /economics /therapeutic use; Administration, Oral; Adult; Antiviral Agents /therapeutic use; Chickenpox /drug therapy; Cost-Benefit Analysis; Humans; Quality of Life; Quality-Adjusted Life Years AccessionNumber Page: 4 / 5

5 Powered by TCPDF ( Date bibliographic record published 30/11/1998 Date abstract record published 30/11/1998 Page: 5 / 5