BACKGROUND
Psoriasis is a common immune disease characterized by thick scaly red lesions and systemic comorbidities. Psoriasis has an enormous effect on patients’ lives, reducing health-related quality of life to an extent similar to that seen with other major medical conditions.1 The total cost of psoriasis to society encompasses third-party medical and prescription drug costs, patient expenditures for over-the counter medicines, lost work time, reduced productivity, and diminished quality of life. Estimates of direct psoriasis costs alone in the United States (US) in US dollars, year 2013 values, ranged from $51.7 to $63.2 billion per annum, with the annual US cost of psoriasis to society approximating $112 billion.2 A large number of treatments are available for moderate-to-severe psoriasis, ranging from phototherapy to systemic agents, including adalimumab, etanercept, infliximab, secukinumab, ustekinumab, and ixekizumab. Ixekizumab is a high-affinity monoclonal antibody that selectively targets interleukin-17A.3 The efficacy and safety of ixekizumab were established in three randomized clinical trials, including two prospective, double-blind, multicenter, international, phase 3 studies (UNCOVER-2 [NCT01597245] and UNCOVER-3 [NCT01646177]) that compared ixekizumab and etanercept with placebo. In both UNCOVER-2 and UNCOVER-3, ixekizumab was more effective than etanercept.4 The Psoriasis Area and Severity Index (PASI) is the most commonly utilized outcome measure for efficacy evaluation in clinical trials; success is often measured by the proportion of people who achieve at least a 75% reduction in PASI score from baseline (PASI 75). However, patients prefer even greater levels of clearing,5–6 and newer psoriasis treatments achieve these greater levels of improvement (90% and 100% reductions in PASI scores) more frequently.7 To allow healthcare decision makers to compare the relative cost per additional responder needed to achieve higher levels of clearance (PASI 90 and PASI 100 response rates) across
