The cost effectiveness and budget impact of natalizumab for formulary inclusion

Crohn's disease (CD) and multiple sclerosis (MS) are debilitating autoimmune diseases, which represent a substantial cost burden in the context of managed care. As a corollary, there is an unmet pharmacotherapeutic need in patient populations with relapsing forms of MS, in addition to populations with moderately to severely active CD with evidence of inflammation who have experienced an inadequate response to other mainstream therapies. The purpose of this study was to analyze the clinical and economic data associated with natalizumab (Tysabri) and to determine the potential impact of its formulary inclusion in a hypothetical health plan.

Regarding MS, the implemented cost-effectiveness and budget-impact models demonstrated an anticipated reduction in relapse rate of 67% over 2 years, and a total therapy cost of $72,120 over 2 years, equating to a cost per relapse avoided of $56,594. With respect to the model assumptions, the market share of natalizumab would experience an increase to 8.5%, resulting in a total per-member, per-month healthcare cost increase of $0.003 ($0.002 for pharmacy costs and $0.001 for medical costs). Regarding CD, over a 2-year period outlined by the model, natalizumab produced the highest average time in remission, steroid-free remission, and remission or response in comparison to the other agents. The mean total costs associated with the initiation of natalizumab, infliximab, and adalimumab were $68,372, $62,090, and $61,796, respectively. Although natalizumab's costs were higher, the mean time spent in remission while on this medication was 4.5 months, as opposed to 2.4 months for infliximab and 2.9 months with adalimumab. This shift in market share was used to estimate the change in total costs (medical + pharmacy), and the per-member per-month change for the model's base case was calculated to be $0.035.

The aforementioned cost-effectiveness results for natalizumab in the treatment for CD and MS were limited by the model's predetermined assumptions. These assumptions include anticipated reduction in relapse rate after 2 years of therapy and acquisition costs in the MS model, as well as assuming a certain percentage of patients were primary and secondary failures of TNFalpha inhibitor therapy in the CD model.

The evidence presented here demonstrates that natalizumab provides clinical practitioners with another tool in their fight against both MS and CD, albeit by way of a different mechanism of action. After a thorough review of the evidence, the authors find that natalizumab has been shown to be relatively cost effective in the treatment of both conditions from a payer perspective; the therapy adds a new option for those patients for whom conventional treatment was unsuccessful.