856. Treatment-Resistant Schizophrenia: Definitions, Current Pharmacological Strategies, and Emerging Pipeline Therapies

Abstract

Abstract Background Antipsychotic monotherapy is the guideline-supported mainstay of treatment for schizophrenia. However, approximately 40% of patients fail to achieve an adequate response in randomized controlled trials, highlighting the significant clinical challenge of treatment-resistant schizophrenia (TRS). Despite clozapine being the gold standard for TRS, its use is often limited by concerns over its side effect profile and the need for mandatory blood monitoring. Furthermore, real-world evidence indicates that clinicians frequently prefer antipsychotic combinations over initiating clozapine. Aims & Objectives This lecture aims to provide a comprehensive overview of treatment resistance in schizophrenia. It will cover the definitions of TRS, provide an updated and detailed analysis of clozapine’s efficacy and side effect profile, examine the impact of illness duration on treatment response, and present a hierarchical ranking of pharmacological strategies through a network meta-analysis. Emerging non-pharmacological treatments will also be discussed. Method The presentation synthesizes data from multiple meta-analyses and systematic reviews, including: Clozapine Side Effect Profile: Analysis of 116 RCTs (n=8431) comparing clozapine to other antipsychotics (https://doi.org/10.1192/bjp.2025.10421) Response Rates and Illness Duration: Meta-analysis of 60 RCTs (n=11,375) examining clozapine response rates in non-TRS and TRS populations, and the nonlinear association with illness duration (https://www.nature.com/articles/s44220-026-00604-w ) Comparative Efficacy: A network meta-analysis (NMA) of 150 RCTs (n=11,375) evaluating 78 drug options, including antipsychotic monotherapies and combinations, for TRS (https://doi.org/10.1016/j.eclinm.2025.103291 ) Emerging Strategies: An unpublished systematic review including psychotherapy and neuromodulatory interventions (rTMS, ECT). Results Clozapine Safety: In 69 monotherapy RCTs, clozapine showed no significant difference from other antipsychotics in mortality or discontinuation due to adverse effects. However, it significantly increased the risk of seizures (RR 3.61, prevalence 3.1%), orthostatic hypotension/bradycardia/syncope (RR 1.66, prevalence 11%), and nearly tripled the risk of agranulocytosis (RR 2.81, prevalence 0.7%). In 47 combination RCTs, clozapine combinations were not associated with an increased risk of severe adverse effects like agranulocytosis or seizures. Response & Timing: Clozapine demonstrated a 81% response rate in non-TRS and 63% response rate in TRS patients. Response rates declined steeply in the first decade of illness (from >90% at onset to ~46% by year 10), after which they stabilized, underscoring a critical window for intervention. Comparative Efficacy: The NMA found clozapine monotherapy to be superior to several other antipsychotics. Certain clozapine combinations showed superior efficacy for overall, positive, and negative symptoms compared to clozapine monotherapy, though confidence in most estimates was low to very low. Data also suggested that some antipsychotic combinations may outperform monotherapy. Higher baseline severity was associated with higher clozapine efficacy. Discussion & Conclusions The findings reaffirm clozapine’s superior efficacy for TRS while providing an updated comprehensive view of its safety profile, which may help clinicians better weigh risks and benefits. The evidence of a critical window for treatment response highlights the urgent need for early identification of TRS and prompt clozapine initiation. While the network meta-analysis suggests that some clozapine combinations may offer additional benefits, the low confidence in these estimates necessitates cautious interpretation. The gap between guideline recommendations and real-world prescribing practices—where combinations are often favored over clozapine—must be addressed through education and system-level changes.