|Cost utility of photodynamic therapy for predominantly classic neovascular age related macular degeneration
|Hopley C, Salkeld G, Mitchell P
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.
The study examined photodynamic therapy (PDT) as treatment for choroidal neovascularisation (CNV). The comparator treatment was placebo.
The hypothetical study population comprised patients with reasonable (model 1) or poor (model 2) initial visual acuity in the better seeing eye, predominantly classic CNV in that eye, poorer vision in the fellow eye, with an average age of 75 years.
The setting was primary care. The model data were derived from Australian studies. However, the costs were converted to UK pounds sterling and the treatment was assumed to have been carried out in the UK.
Dates to which data relate
The dates of the clinical study from which the effectiveness data were obtained were not stated. However, the paper reported that the costs and quality-adjusted life-years (QALYs) were adjusted to the reference year of 2003.
Source of effectiveness data
The effectiveness data were derived from a review and synthesis of completed studies.
The authors used a decision analysis model over 7 years to estimate annual incremental utility values and associated costs.
Outcomes assessed in the review
The outcomes assessed were:
the expected mortality rates,
the increased mortality rates associated with AMD, and
an AMD-related utility valuation.
Study designs and other criteria for inclusion in the review
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 authors appear to have used 3 primary studies in the review.
Methods of combining primary studies
Investigation of differences between primary studies
Results of the review
The decrease in the absolute risk of developing 3 lines or more vision loss with PDT treatment was 28% over 2 years.
The initial visual acuity utility for model 1 was 0.81 (95% confidence interval, CI: 0.73 - 0.89).
The loss of 3 lines of visual acuity utility for model 1 was 0.57 (95% CI: 0.47 - 0.67).
The initial visual acuity utility for model 2 was 0.52 (95% CI: 0.38 - 0.66).
The loss of 3 lines of visual acuity utility for model 2 was 0.40 (95% CI: 0.29 - 0.50).
The weighted average expected lifespan for a TAP study patient was 7 years.
Measure of benefits used in the economic analysis
QALYs were used to measure benefit in the economic analysis. The QALYs were calculated by multiplying each year in a given state by a utility score for that state. The benefits were discounted at 6%, which is the recommended rate. The authors stated that the source paper for the AMD-related utility values (Brown et al., see Other Publications of Related Interest) established utilities using time trade-off methodology for different ranges of best corrected visual acuity in the better eye. Further details were not given.
The study only included the variable incremental costs. These were initial consultation, fluorescein angiogram, verteporfin 15 mg vial, procedure, and subsequent consultations. These costs were identified by reviewing the literature and were supplemented by expert opinion on AMD resource use. The schedule fees were obtained from published 2003 Australian Medicare Benefits Schedule data. This is the schedule of fees against which the government reimburses the providers of medical services. All other costs were assumed to be the same in both the treatment and placebo arms, and were therefore not examined. The resource quantities were not reported separately. The costs were discounted at the recommended rate of 6%.
Statistical analysis of costs
The costs were treated deterministically.
The indirect costs were not included.
Australian dollars (Aus$) and UK pounds sterling (). Purchasing Power Parity (PPP) rates were used to convert costs between currencies. The reference year was 2003.
A preliminary analysis of the models using a fixed percentage change in input values was conducted on the relevant variables. The variables that most affected the incremental cost-effectiveness ratios were selected for further examination using a one-way sensitivity analysis. These were the incremental utility value, percentage risk reduction, continuing annual PDT treatments, and discount rate for QALYs and costs. No justification was given for the range of values used in the sensitivity analyses.
Estimated benefits used in the economic analysis
Model 1 resulted in an incremental adjusted QALY of 0.395 for a modelled total of 10.9 PDT treatments.
Model 2 resulted in an incremental adjusted QALY of 0.197 for a modelled total of 10.9 PDT treatments.
The time period was 7 years.
The total cost for both models was 12,478.
Synthesis of costs and benefits
The benefits and costs were combined to estimate a cost per QALY.
The incremental cost per QALY was 31,607 for model 1 and 63,214 for model 2.
Sensitivity analyses in model 1 produced incremental cost-effectiveness ratios ranging from 25,285 to 37,928 per QALY. The lowest ratio was associated with higher incremental utility values.
Sensitivity analyses in model 2 produced incremental cost-effectiveness ratios ranging from 54,183 to 75,856 per QALY. The lowest ratio was associated with higher incremental utility values.
Photodynamic therapy (PDT) is at least moderately cost-effective in people with reasonable visual acuity, given the assumptions made in the model. However, for those with poor initial visual acuity, PDT is relatively cost ineffective.
CRD COMMENTARY - Selection of comparators
The authors compared strategies of PDT with placebo. PDT was not explicitly stated to be current practice, although the authors stated that PDT is currently the only proven therapy for AMD and is now funded by the NHS after a lengthy appraisal study. You should decide if this is appropriate for your setting.
Validity of estimate of measure of effectiveness
The authors did not state that a systematic review of the literature had been carried out. They appear to have used the primary studies selectively. To explore the impact of uncertainty in parameter values, the authors conducted a sensitivity analysis on a number of parameters.
Validity of estimate of measure of benefit
The economic benefit was measured by QALYs, which were estimated using a decision model. The model accounted for the health states that the patients could enter and the probability of moving between the states. The utility weights were taken from published literature.
Validity of estimate of costs
The authors reported the study was conducted from a third-party payer perspective. The indirect costs were not assessed and other costs such as capital expenditure were assumed to be equal in both arms of the model. The price year was stated as 2003 and the method for converting currencies was clearly explained. The source of the cost data was appropriately reported.
The authors converted the costs from Australian dollars to UK pounds sterling using PPP rates. However, they did not state if treatment practices or resource use in the UK would be the same as in Australia. The authors did state that the converted PDT cost figure was comparable to published UK figures, but details were not given.
The authors made appropriate comparisons of their results with those from other studies. The issue of the generalisability of the study results was discussed in that the sensitivity analysis gave a range of effects that enabled robust cost generalisation over similar populations in Europe. The authors acknowledged that some estimates of treatment were pessimistic. However, this would improve the cost-effectiveness ratios. The authors noted further limitations to the study. For example, they did not account for any disutility associated with PDT treatment or the potential benefits of independent living.
Implications of the study
The authors did not make any clear recommendations for policy or practice, other than stating that the findings have implications for ophthalmic practice and health care planning. This refers to the different results apparent, depending on the level of initial visual acuity in a patient.
Source of funding
Supported by an initiating grant from the Westmead Milennium Institute, University of Sydney.
Hopley C, Salkeld G, Mitchell P. Cost utility of photodynamic therapy for predominantly classic neovascular age related macular degeneration. British Journal of Ophthalmology 2004; 88(8): 982-987
Other publications of related interest
Brown GC, Sharma S, Brown MM, et al. Utility values and age-related macular degeneration. Archives of Ophthalmology 2000;118:47-51.
Subject indexing assigned by NLM
Aged; Choroidal Neovascularization /drug therapy /economics /etiology; Cost-Benefit Analysis; Decision Support Techniques; Great Britain; Humans; Macular Degeneration /complications /economics; Models, Econometric; Photochemotherapy /economics /methods; Quality-Adjusted Life Years; Visual Acuity /physiology
Date bibliographic record published
Date abstract record published