Short-term cost-effectiveness of siltartoxatug versus human tetanus immunoglobulin for post-traumatic tetanus prophylaxis in Chinese adults: a trial-based economic evaluation

Tetanus is a vaccine-preventable but potentially fatal post-traumatic infection with substantial healthcare resource use once disease develops. Passive immunization is recommended for patients with tetanus-prone wounds. Human tetanus immunoglobulin (HTIG) is the conventional passive immunizing product, but dependence on human plasma may constrain supply and complicate blood-product handling and management. Siltartoxatug is a recombinant fully human anti-tetanus toxin IgG1 monoclonal antibody that produced earlier and more sustained anti-tetanus neutralizing antibody responses than HTIG in a phase III trial. We conducted a short-term, trial-based, two-arm cost-effectiveness analysis of siltartoxatug 10 mg versus HTIG 250 IU from a Chinese hospital pharmacy perspective. Drug acquisition prices were combined with aggregate response data from the TNM002-301 phase III trial. Effectiveness was defined as the proportion of patients achieving the trial-prespecified increase from baseline in anti-tetanus neutralizing antibody titer (ΔTiter) of at least 0.01 IU/mL at 12 h and 90 days. Outcomes included the natural-unit incremental cost-effectiveness ratio (ICER), expressed as incremental drug cost per additional responder, standardized drug-budget consequences per 1000 eligible patients, deterministic price scenarios, and a restricted probabilistic sensitivity analysis (PSA) of response-rate uncertainty. Per-dose costs were CNY 303.80 for siltartoxatug and CNY 245.38 for HTIG, yielding an incremental cost of CNY 58.42 per patient. Response-rate differences were 42.2% points at 12 h (95.4% vs. 53.2%) and 81.4% points at 90 days (91.5% vs. 10.1%). The corresponding natural-unit ICERs were CNY 138.4 and CNY 71.8 per additional trial-defined responder. Complete hypothetical replacement of HTIG in a standardized cohort of 1000 eligible patients increased drug expenditure by CNY 58,420 and yielded approximately 422 additional 12-h responders and 814 additional 90-day responders. In 10,000 simulations, median ICERs were CNY 139.1 (95% simulation interval 119.6-165.3) at 12 h and CNY 72.2 (68.3–77.4) at 90 days. At the evaluated prices, siltartoxatug produced higher trial-defined immunological response rates than HTIG for a modest incremental drug cost. These results describe drug cost per additional pharmacodynamic responder and standardized budget consequences; they do not establish cost effectiveness against an accepted willingness-to-pay threshold or demonstrate reductions in clinical tetanus, hospitalization, mortality, or quality-adjusted life-years. At the evaluated prices, the natural-unit ICER was CNY 138.4 per additional patient achieving the 12-h trial-defined immunological response and CNY 71.8 per additional patient achieving the 90-day response. The response measure is mechanism-proximal and clinically interpretable for passive immunization, but it has not been validated as a surrogate for clinical tetanus incidence, hospitalization, mortality, or quality-adjusted life-years. The analysis includes drug acquisition costs only and reports standardized replacement scenarios rather than a full budget impact analysis. The restricted PSA and exploratory supplementary CEAC quantify conditional uncertainty but do not establish a national willingness-to-pay threshold.