The Association Between TNF Inhibitor Therapy Availability and Hospital Admission Rates for Patients with Ankylosing Spondylitis. A Longitudinal Population-Based Study.

BACKGROUND

TNF inhibiting drugs (TNFi) provide symptomatic relief for patients with ankylosing spondylitis (AS), but uncertainty remains about long-term benefits. We compared hospital admissions, emergency department (ED) presentations, and direct health care costs before and after the availability of subsidized TNFi therapy for AS patients.

METHODS

State-specific dispensing and cost data for TNFi therapy for AS in Western Australia (WA) were obtained from Pharmaceutical Benefits Scheme (PBS) and expressed as the number of defined daily doses (DDD)/1000 population/day. Linked admission and ED data for 1783 AS patients followed for 14,257 person-years between 1990 and 2015 were extracted. Pre- and post-2005 admission rates/100,000 population were compared by rate ratio (RR).

RESULTS

TNFi uptake in WA reached a DDD/1000 population/day 0.45 at an annual cost of AU$17.7 million in 2020. Hospital admission rates remained unchanged (RR: 0.95, CI 0.71-1.27, p = 0.66) but increased slightly in female patients (RR 1.22; CI 0.91-1.64, p = 0.20). While there was no change in cardiovascular admissions (6.3 vs. 6.2%, p = 0.6) or ED visit rates since 2005, frequency for cancer (2.7 vs. 3.8%, p < 0.01), infection (1.1 vs. 1.7%, p < 0.01) and mental health (4.0 vs. 4.5%, p < 0.02) admissions increased. Associated direct health care costs (2020 values) averaged AU$14.7 million before and AU$ 24.7 million per year after 2005.

CONCLUSIONS

The introduction of subsidized TNFi therapy did not change all-cause hospital admission or ED visit rates for existing AS patients. Whether the significantly increased direct health care costs are offset by reductions in other health care costs remains to be determined.