Analytical approach:
A Markov model was developed to combine the cost and effectiveness data from published sources. The model's cycle length was one year and the time horizon was the patient's lifetime. The authors stated that the perspective was that of the UK NHS.
Effectiveness data:
The effectiveness data for zoledronic acid in retaining bone mineral density (BMD) was from a three-year interim analysis of several published trials. After treatment ceased, zoledronic acid was assumed to have no further effect. BMD without treatment was from a bone subanalysis of a published trial. Mortality in the first five years was from standard sources, and incorporated additional mortality due to hip fracture. After five years, mortality was from published cancer survival data. The main clinical effectiveness estimate was the fracture risk and these data were from published studies.
Monetary benefit and utility valuations:
The utility weights for fractures, including hip fractures that led to nursing home residency, were from published literature. It was assumed that the utility weight was reduced for one year, before recovering to a level between that of the first year after fracture and that before the fracture.
Measure of benefit:
The primary measure of benefit was quality-adjusted life-years (QALYs) and these were discounted at 3.5% per annum.
Cost data:
The cost categories were drug acquisition; medical supplies to administer zoledronic acid; physician and nurse time; physician visits; BMD scans; and fracture treatment. The drug acquisition costs were from the British National Formulary. Other costs were from published literature. The costs were reported in 2007 UK pounds sterling (£) and discounted at 3.5% per annum.
Analysis of uncertainty:
The uncertainty was explored, using probabilistic sensitivity analysis, with 1,000 simulations. Normal distributions were assumed for the changes in BMD and the relative risk of subsequent fracture. Beta distributions were assumed for the utilities, gamma for the costs, and triangular for the percentage of hip fractures leading to nursing home residency. The results of this sensitivity analysis were presented in a cost-effectiveness acceptability curve.