4CPS-198 Clozapine monitoring: efficacy, safety and the influence of smoking on plasma levels

<h3>Background and Importance</h3> Monitoring clozapine plasma levels is crucial to optimise treatment efficacy and minimise haematological toxicity risks, including agranulocytosis and leukopenia. Additionally, smoking significantly affects clozapine metabolism, leading to lower plasma concentrations and potential subtherapeutic effects, emphasising the need for tailored monitoring in patients. <h3>Aim and Objectives</h3> To analyse the treatment of patients with schizophrenia and psychosis using clozapine, focusing on its efficacy and safety. The assessment was conducted by determining trough plasma concentrations of clozapine. <h3>Material and Methods</h3> A retrospective observational study was carried out involving patients diagnosed with schizophrenia or psychosis treated with clozapine. Clozapine plasma levels were measured between January 2023 and September 2024. The variables collected included sex, age, diagnosis, smoking habits, dose, trough plasma levels (therapeutic range: 250–700 ng/mL), and haematological toxicity parameters (leukopenia, neutropenia, eosinophilia, and thrombocytopenia). Additionally, dose adjustment recommendations were made when necessary, and the acceptance of these recommendations was evaluated. <h3>Results</h3> The study included 31 patients, with a median age of 46 years (range 20–67), of whom 17 were male. Most patients were diagnosed with schizophrenia (90.3%) or psychosis (9.7%), and 19 patients were smokers. A total of 75 clozapine plasma levels were measured, with 42 falling outside the recommended therapeutic range (34 subtherapeutic and 8 supratherapeutic). Dose adjustment recommendations were made in these cases, but 20 (47.6%) were not accepted due to the good clinical condition of the patients. The average clozapine dose was similar in smokers (320 mg) and non-smokers (350 mg). However, average trough plasma concentrations were nearly half in smokers (239 ng/mL) compared to non-smokers (530 ng/mL). No cases of leukopenia, neutropenia, or eosinophilia were observed. Six cases of thrombocytopenia (&lt;150,000/mm³) were recorded, but none were severe (&lt;50,000/mm³). <h3>Conclusion and Relevance</h3> Some patients benefit from clozapine treatment despite subtherapeutic plasma levels. Smoking significantly lowers clozapine plasma concentrations. Monitoring clozapine levels is essential to ensure both the safety and efficacy of the treatment. <h3>References and/or Acknowledgements</h3> <h3>Conflict of Interest</h3> No conflict of interest