High-dose olanzapine in treatment-resistant schizophrenia: a systematic review

BACKGROUND: Treatment-resistant schizophrenia (TRS) affects approximately 30% of people with schizophrenia. Clozapine is the gold standard treatment for TRS but is not always suitable, with a proportion of individuals intolerant of side effects or unable to engage in necessary blood monitoring. Given the profound impact TRS can have on those affected, alternative pharmacological approaches to care are needed. OBJECTIVES: To review the literature on the efficacy and tolerability of high-dose olanzapine (>20 mg daily) in adults with TRS. DESIGN: This is a systematic review. DATA SOURCES AND METHODS: We searched for eligible trials published prior to April 2022 in PubMed/MEDLINE, Scopus and Google Scholar. Ten studies met the inclusion criteria [five randomised controlled trials (RCTs), one randomised crossover trial and four open label studies]. Data were extracted for predefined primary outcomes (efficacy, tolerability). RESULTS: Compared with standard treatment, high-dose olanzapine was non-inferior in four RCTs, three of which used clozapine as the comparator. Clozapine was superior to high-dose olanzapine in a double-blind crossover trial. Open-label studies demonstrated tentative evidence in support of high-dose olanzapine use. It was better tolerated than clozapine and chlorpromazine in two respective RCTs, and was generally well tolerated in open-label studies. CONCLUSION: This evidence suggests high-dose olanzapine is superior for TRS when compared with other commonly used first- and second-generation antipsychotics, including haloperidol and risperidone. In comparison with clozapine, the data are encouraging for the use of high-dose olanzapine where clozapine use is problematic, but larger, better designed trials are needed to assess the comparative efficacy of both treatments. There is insufficient evidence to consider high-dose olanzapine equivalent to clozapine when clozapine is not contraindicated. Overall, high-dose olanzapine was well tolerated, with no serious side effects. REGISTRATION: This systematic review was preregistered with PROSPERO [CRD42022312817].