Cost effectiveness of the two-compound formulation calcipotriol and betamethasone dipropionate gel in the treatment of scalp psoriasis in Scotland.

To compare the cost effectiveness of the two-compound formulation (TCF) calcipotriol plus betamethasone dipropionate gel used first-, second- or third-line to standard topical treatments for moderately severe scalp psoriasis from a Scottish NHS perspective. Treatment pathways for scalp psoriasis patients in primary care were defined by Scottish prescribing statistics, an interview programme and published sources. The extensive 1-year Markov model included 12 different topical treatment pathways, each simulating three lines of therapy. Seven pathways contained the TCF gel in first-, second- or third-line. The remaining five pathways were included as comparators, reflecting the heterogeneity across clinical practice. The cost effectiveness of TCF gel was compared to the average of five non-TCF gel pathways. The clinical effectiveness measure was the ability of topical treatments to control disease at 4 weeks. Response rates were derived from indirect comparisons of ten randomised controlled trials. Utilities were elicited from SF-36 (v2) scores in one TCF gel trial. The main outcome was the incremental cost per quality-adjusted life-year (QALY). Extensive sensitivity analyses were performed to assess the robustness of the results. TCF gel used first-, second- or third-line was projected to increase QALYs (around 0.0025) with cost savings per patient (£20-30) over 1 year. The study analysis acknowledged a number of limitations including lack of quality comparator data, the need to make assumptions in the absence of evidence and lack of model validation. However the results showed that TCF gel was the dominant treatment strategy across a broad range of credible scenarios. Scalp psoriasis is difficult to treat. Many different topical preparations can be used but several factors such as greasiness, irritation, time needed to apply, and lack of efficacy often result in reduced adherence to treatment regimens. Where cosmetic properties are important for patient acceptability and compliance is a major issue contributing to treatment failure, the once-daily TCF gel offers patients with scalp psoriasis an attractive, cost-saving treatment option.