Effects on monotherapy and reduction of antipsychotic drugs by clozapine therapy in Japanese patients with treatment-resistant schizophrenia

What is known and objective The schizophrenia guidelines in Japan and many other countries describe clozapine as the first-choice drug for patients with treatment-resistant schizophrenia. However, there have been no reports to date on the effects of the introduction of clozapine on the prescription of other antipsychotics and concomitant drugs. Methods In this study, we retrospectively investigated the prescription of antipsychotics and concomitant drugs before vs 6 months after and 12 months after switching to clozapine. Results and discussion Clozapine was introduced to 62 patients with treatment-resistant schizophrenia, and 51 patients continued on clozapine therapy. Six months after switching to clozapine, there was a significant decrease in the mean number of antipsychotic drugs (2.04 +/- 0.75 vs 1.10 +/- 0.30: p < 0.001) and in the mean chlorpromazine equivalent value (1024 +/- 73 mg/day vs 781 +/- 391 mg/day: p < 0.001) compared to before switching. Moreover, antipsychotic monotherapy increased from 24% to 90% after switching to clozapine. In addition, the number of concomitant benzodiazepines, anti-parkinson drugs and antidepressants also significantly decreased 6 and 12 months after switching to clozapine (p < 0.001 for benzodiazepines and anti-parkinson drugs, and p < 0.05 for antidepressants). What is new and conclusion Our study suggests that switching to clozapine may reduce the use of antipsychotic combination therapy, and may also reduce the number of concomitant drugs.