Background Spending on biological agents has risen dramatically due to the high cost of the drugs and the increased prevalence of spondyloarthritis. Objective To evaluate the annual cost per patient and cost for each biological drug for treating patients with spondyloarthritis from 2009 to 2016, and to calculate factors that affect treatment cost, such as optimizing therapies by monitoring drug serum levels, the use of biosimilar-TNF inhibitors, and official discounts or negotiated rebates in biologicals acquired by the pharmacy department. Method Retrospective, observational study in a Spanish tertiary hospital. Main outcome Annual cost per patient and per drug. Factors that influenced the costs and socio-demographic parameters and disease activity. Results A total of 129, 215, and 224 patients were treated in 2009, 2013, and 2016, respectively. The annual cost per patient decreased: EUR11,604 in 2009, EUR8513 in 2013, and EUR7464 in 2016. The introduction of new drugs drives economic competition, leading to total savings per drug, with discounts reaching 5.8, 12.4, 16.7, 17.7, 13.7, and 24.8% for original infliximab, etanercept, adalimumab, ertolizumab, golimumab, and secukinumab, respectively, while rebates for biosimilar infliximab reached 31.90% in 2016. The number of patients with optimized therapies reached 47.5% in 2016, which led to cost savings of EUR798,614, in addition to savings from official discounts and rebates of EUR252,706 and savings from optimized therapies of EUR545,908 in 2016. Conclusion The cost of biological treatments declined after official discounts, negotiated rebates, and optimized therapies, leading to a significant decrease in the annual cost per patient. The greatest contribution to economic savings in biological therapy according to our study was biological therapy optimization.