This economic evaluation used a Markov model based on individual patient simulations to examine the clinical and economic impact of the two treatments. The time horizon of the analysis was 12 weeks. The authors reported that the perspective of the Spanish National Health Care System was adopted.
The clinical data were derived from a selection of known, relevant studies. Specifically, treatment effect for the two drugs was derived from three randomised controlled trials (RCTs), which were double-blind and placebo-controlled. The data on PGB were derived from a single trial, while data on GBP were obtained from two studies. Thus, no head-to-head trials were used as a source of clinical effectiveness. The patient characteristics were taken from the PGB trial. The key clinical outcome was reduction in pain with the two drugs.
Monetary benefit and utility valuations:
The utility valuations were derived from a combined analysis of two cross-sectional studies carried out on Spanish patients using the Spanish version of the Leeds Assessment of Neuropathic Symptoms and Signs and the Douleur Neuropathique Four scales. These were converted into utility weights using the Spanish version of the Health Utility Index Mark Three and a visual analogue scale.
Measure of benefit:
The summary benefit measures were quality-adjusted life-years (QALYs), days with no or mild pain, and number of patients with no or mild pain.
The direct medical costs were drugs, outpatient visits to specialists and the pain clinic, diagnostic tests, and non-pharmacological treatments. The side effects of the drugs had a negligible impact and were not included. The resource quantities were reported for different levels of pain intensity and unit costs were reported. The resource use for most items was determined from a panel of 13 experts in Spain. The direct health care costs were derived from a national health cost database. Drug costs were valued using public sales prices obtained from the Catalogue of Medicinal Products of the Spanish General Council of Official Pharmaceutical Colleges. All costs were in Euros (EUR) and the price year was 2006.
Analysis of uncertainty:
The decision model was replicated for 1,000 samples of 1,000 patients each to allow the calculation of 95% confidence interval (CI)s for cost-utility and cost-effectiveness ratios. A probabilistic sensitivity analysis focused on variations in weekly mean pain changes. A deterministic sensitivity analysis investigated alternative assumptions and scenarios, especially around cost assumptions and utility values.