OBJECTIVES: To compare the prevalence, regulations, and pharmacovigilance practices of clozapine use in Eastern European countries (except Russia). METHODS: Questionnaires and data from administrative databases (2016 and 2021), package inserts and national guidelines were collected from 21 co-authors from 21 countries. Reports of clozapine adverse drug reactions (ADRs) sent to the global pharmacovigilance database (VigiBase™) were analyzed from introduction to December 31, 2022. RESULTS: Clozapine prescription among antipsychotics in 2021 varied six-fold across countries, from 2.8 % in the Czech Republic to 15.8 % in Montenegro. The utilization of antipsychotics in both 2016 and 2021 was highest in Croatia, and lowest in Serbia in 2016, and Montenegro in 2021, which had half the defined daily dose (DDD)/1000/day compared to the Croatian data. From 2016 to 2021, the prevalence of antipsychotic use increased in almost all countries; the proportion of clozapine use mainly remained unchanged. Differences were detected in hematological monitoring requirements and clozapine approved indications. Only a few national schizophrenia guidelines mention clozapine-induced myocarditis or individual titration schemes. The VigiBase search indicated major underreporting regarding clozapine and its fatal outcomes. By comparison, the United Kingdom had less than half the population of these Eastern European countries but reported to VigiBase more clozapine ADRs by 89-fold and clozapine fatal outcomes by almost 300-fold. CONCLUSION: Clozapine is under-utilized in Eastern European countries. Introducing individualized clozapine treatment schedules may help to maximize clozapine benefits and safety. Major improvement is needed in reporting clozapine ADRs and fatal outcomes in Eastern European countries.

Bureau of Pharmacovigilance Department of Post authorisation Safety State Agency of Medicines Estonia

Center for Drug Sciences Faculty of Pharmacy University of Medicine and Pharmacy Carol Davila Bucharest Romania

County Hospital Dr Fra Mihovil Sučić Livno Svetog Ive 2 Livno 80101 Bosnia and Herzegovina

Department of Internal Medicine Dermatology and Psychiatry School of Medicine University of La Laguna Canary Islands Spain; Instituto Universitario de Neurociencia Universidad de La Laguna San Cristóbal de La Laguna Spain

Department of Physical Medicine and Pharmacology School of Medicine Universidad de La Laguna Canary Islands Spain; Hospital Universitario de Canarias Tenerife Spain

Department of Psychiatry and Medical Psychology Belarusian State Medical University Minsk Belarus

Department of Psychiatry and Narcology Riga Stradinš University Riga Latvia; Department for Depression and Crisis Riga Center of Psychiatry and Narcology Riga Latvia

Department of Psychiatry Medical University of Gdańsk Gdańsk Poland

Department of Psychiatry Psychotherapy and Psychosomatics Hospital of Psychiatry University of Zurich Zurich Switzerland

Department of Psychiatry University Medical Centre Maribor Maribor Slovenia

Department of Social and Behavioural Medicine Faculty of Medicine Pavol Jozef Safarik University Kosice Slovakia

Medical Faculty University of Montenegro Psychiatric Clinic Clinical Centre of Montenegro Podgorica Montenegro

Mental Health Research Center at Eastern State Hospital Lexington KY United States of America; Biomedical Research Centre in Mental Health Net Santiago Apostol Hospital University of the Basque Country Vitoria Spain

National Institute of Mental Health Klecany Czech Republic; Department of Psychiatry Charles University 3rd Faculty of Medicine Prague Czech Republic

National Institute of Mental Health Neurology and Neurosurgery Budapest Hungary

Psychiatric Clinic Lithuanian Health Sciences University Kaunas Hospital Lithuanian Health Sciences University Kaunas Lithuania

Psychiatric Clinic University Hospital Prof Dr Stoyan Kirkovich Trakia University Stara Zagora Bulgaria

Psychiatric Services of Center of Psychosocial Recovery Yerevan Armenia; Department of Applied Psychology of the Armenian State Pedagogical University named after Kh Abovyan Yerevan Armenia

School of Medicine University of Zagreb Zagreb Croatia; University Hospital Centre Zagreb Zagreb Croatia

State University of Medicine and Pharmacy Nicolae Testemitanu Chişinău Republic of Moldova

Tbilisi State Medical University Department of Psychiatry Tbilisi Georgia

University Clinic of Psychiatry Medical Faculty University Ss Cyril and Methodius Skopje North Macedonia

University Hospital Center Mother Teresa Tirana Albania

University of Kragujevac Faculty of Medical Sciences Department of Psychiatry Kragujevac Serbia

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