Tumor Necrosis Factor Inhibitors in Patients with Psoriatic Arthritis

San Francisco—Due to a lack of head-to-head studies demonstrating the comparative effectiveness of tumor necrosis factor inhibitors (TNFi), only indirect comparisons can be made, according to researchers. The National Institute for Health and Clinical Excellence (NICE) has created methods of indirect comparisons and provided background research for cost-effectiveness analyses.

Researchers recently conducted a study to assess the economic impact of TNFi in patients with psoriatic arthritis (PsA) over 1 year from the perspective of a US commercial payer. They reported results of the study at a poster session at the AMCP meeting. The poster was titled Number Needed to Treat, Cost per Responder, and Budget Impact of Long-Standing Tumor Necrosis Factor Inhibitors in Psoriatic Arthritis.

The researchers utilized data for comparative clinical response rates from a 2011 Health Technology Assessment (HTA) report within a NICE independent systematic review of 10 electronic databases of TNFi, adalimumab (ADA), etanercept (ETA), and infliximab (IFX) in patients with PsA. The data included randomized controlled trials (RCTs) of the specified TNFi, when used after failure on standard treatments (including disease-modifying antirheumatic drugs) up to and including data available as of June 2009.

The outcomes of interest in the current study were PsA response criteria (PsARC), Psoriasis Area and Severity Index (PASI) 50/75.9% response, and American College of Rheumatology Improvement Criteria (ACR) 20/50/70% response. Relative placebo-adjusted response rate differences from the RCTs were assumed to be maintained for 1 year, and annual cost data were included on biologic drug costs.

The TNFi drug costs assumed full compliance on labeled dosing and included all costs sourced from wholesale acquisition costs. The dosages were as follows: ADA, 40 mg every 2 weeks, 26 injections/year; ETA, 50 mg every week, 52 injections/year; and IFX, 5 mg/kg for average 80 kg patient, 4 infusions/year (administration costs of $177.70 per infusion based on a 2-hour infusion). Assuming full compliance, the annual drug costs in US dollars were: ADA, $24,913; ETA, $23,527; and IFX, $24,145.

The researchers divided the US annual drug costs by the NICE response rates for each outcome. The inverse of the response rates, multiplied by 100, generated the number needed to treat (NNT) to achieve 100 responders for each outcome. This figure was multiplied by the annual biologic costs to determine the required budget to achieve 100 responders for patients started on each TNFi.

According to the conclusions in the HTA report, “the results of the evidence synthesis found that IFX appears to be the most effective of the 3 biologics. An indirect analysis found that across all outcomes at 12 weeks (PsARC, ACR, and PASI) infliximab is associated with the highest probability of response.” Those differences led to the lowest derived cost per responder, NNT, and budget impact over 1 year.

Compared with starting patients on IFX, the cost to treat 100 PsARC responders for 1 year would be $2.948 million higher with ADA and $0.647 million higher with ETA.

Limitations cited by the researchers included limiting data to 6 studies, and lack of data from every study for every outcome for all tine points.

The researchers said that, “The results of this research suggest that there may be substantial incremental budget implications for US payers when PsA patients are initiated on ADA or ETA rather than IFX…Within a treatment decision-making context, this type of analysis may be useful.” They added that, “further sensitivity analyses based on indirect comparison credible limits are warranted.”

This study was supported by Janssen Scientific Affairs, Inc.