[The use of metamizole as a risk factor in the occurrence of agranulocytosis].

The risk of agranulocytosis following the use of metamizole was studied by the method of controlled cases. All cases of agranulocytosis and their control cases in Sofia for the period 1982-1986 were included in the study. The mean agranulocytosis morbidity for this period was 3.16 cases for one million population for one year. The etiologic fraction was 7.1%. The relative risk of agranulocytosis following the use of metamizole is 1.25, the maximal risk is 0.03 cases for one million persons using metamizole for one year and the maximal lethal risk is 0.007 cases for one million persons using metamizole for one year. The use of metamizole in Bulgaria for the same period was studied, too. The data presented as a number of defined daily doses used by 1000 population for one day show that the use of metamizole in this country is high. A tendency toward an increase of 7.3% per year was found during the investigation. At the same time the agranulocytosis morbidity remained constant during the period of investigation. The results of the study lead to the conclusion that the use of metamizole is not related to a higher risk of agranulocytosis.