Research topic: Health economics of biological agents in Australia.

Abstract

Tumor necrosis factor (TNF) antagonists infliximab (IFX) and adalimumab (ADA) successfully induce and maintain remission in refractory Crohn's disease (CD) and ulcerative colitis (UC). Anti-TNF agents are associated with high costs, and their use is governed by the national Pharmaceutical Benefits Scheme (PBS). Analyses of the temporal trends and geographical distribution of anti-TNF usage and costs may identify inequity in access to drug and ensure cost-containment and sustainability of this drug class. We conducted a study to examine the Australian and state-based use and cost of IFX and ADA for treatment of luminal and fistulizing CD and acute severe UC under the PBS between January 2007 and July 2014. Prospectively collected PBS data were analyzed, data contained monthly number of prescriptions and expenditure for each PBS item code specific for disease indication, and were separated into Australian states and territories. From 2007 to 2014, a total of 167 213 prescriptions were written for combined CD and UC (IFX: 49 956; ADA: 117 257) with a total expenditure of $380 million (IFX: A$158 million; ADA: A$222 million) (Fig. 1). Drug expenditure increased linearly by a mean of $15 million every year. IFX annual prescription numbers increased fourfold over the study period whereas ADA by sixfold. ADA prescription exceeded IFX after December 2008, with expenditure rising from 51% (2008–2009) to 57% (2013–2014) of total cost. True biologic usage and costs were consistent with projected ranges by the pharmaceuticals benefits advisory committee (PBAC). For example, the cost of infliximab for luminal CD was $12 million and within the PBAC predicted range of $10–30 million. Marked geographical heterogeneity in anti-TNF usage was observed, where most prescriptions were made in the southern states of Tasmania (TAS), Victoria, and South Australia, with least prescriptions in Northern Territories (NT) after accounting for estimated IBD patient population. Latitude strongly predicted for the annual anti-TNF prescriptions per IBD patient (R2 = 0.86; P = 0.001). Use of anti-TNF in TAS was 3.3-fold higher than in the NT. This may indicate higher disease prevalence or more severe disease in the southern states. Possible confounders include differing patient access to care and state-based treatment practices, but speculative IBD environmental risk factors include geographical differences in temperature, sunlight exposure, microbiome, and vitamin D level. In summary, both IFX and ADA usage are increasing exponentially with ADA increasing more rapidly than IFX, while still remaining within PBAC predictions, which supports PBS sustainability. Biosimilar drugs are an avenue that should be explored, as introduction to PBS can lead to cost reductions of up to $79 million annually for IBD alone. Heterogeneity of biologic access was observed across Australian states and territories, with greater use associated with southern latitude, and this raises speculation for environmental influences on the disease.