Ten-Year Public Expenditure Savings Associated with TNF Inhibitor Biosimilars under Australia's Pharmaceutical Benefits Scheme.

Biologic therapies are a major and growing driver of pharmaceutical expenditure globally, with tumor necrosis factor (TNF) inhibitors among the most widely used and costly biologics. In Australia, these therapies are funded through the Pharmaceutical Benefits Scheme (PBS), where biosimilars offer lower cost alternatives; however, the long-term public expenditure impact of TNF inhibitor biosimilars under regulated pricing systems has not been comprehensively quantified. We conducted a retrospective, population-level expenditure analysis using publicly available PBS Item Reports data from 2015 to 2025 to estimate PBS cost savings associated with the listing of adalimumab, etanercept, and infliximab biosimilars for inflammatory arthritis. Counterfactual scenarios were constructed to estimate expected expenditure in the absence of biosimilar entry, explicitly accounting for key PBS pricing mechanisms, including mandatory price reductions and price-disclosure cycles. Biosimilar listing was associated with cumulative PBS savings of AU$562.3 million over the study period. Etanercept biosimilar generated the largest absolute savings (AU$341.5 million; 23.7% reduction), whereas adalimumab biosimilars generated smaller relative savings (AU$195.3 million; 9.4% reduction), reflecting delayed biosimilar entry despite high utilization. Most savings accrued in rheumatoid arthritis, followed by ankylosing spondylitis and psoriatic arthritis. In conclusion, TNF inhibitor biosimilars were associated with substantial and sustained reductions in public medicine expenditure in Australia. The magnitude of savings varied markedly by molecule and was jointly determined by the timing of biosimilar entry and statutory pricing mechanisms, illustrating how regulated reimbursement systems shape realized biosimilar value.