Hematological parameters in patients with chronic pain on long-term dipyrone therapy followed in a tertiary hospital: a retrospective cohort study.

BACKGROUND: Chronic pain is a significant public health problem, with high prevalence and substantial impact on quality of life and costs in healthcare, particularly in the context of ongoing opioid abuse crises in many countries. Chronic pain management often involves a multimodal approach. Dipyrone or metamizole has been used widely for several decades as a non-opioid analgesic. Despite its effectiveness, concerns regarding potential side effects, such as agranulocytosis, have led to its ban in several countries. This study aimed to describe changes in erythrocyte, leukocyte, neutrophil, and platelet counts among patients with chronic pain receiving dipyrone therapy for longer than six months. METHODS: A retrospective cohort study was conducted using data manually collected from medical records of patients treated at the Pain Outpatient Clinic of a tertiary hospital in Brazil, between 2012 and 2022. The research was registered and approved by the institutional ethical Committee. A total of 1,880 adult patients with chronic pain of different causes who received well documented continuous dipyrone therapy for at least six months. Blood counts before dipyrone use and at the end of dipyrone therapy were evaluated. A control group of chronic pain patients not exposed to dipyrone was not available, which represents a major limitation. Statistical analyses such as paired t-tests, Pearson correlations, and multivariate regression were performed to assess changes in blood cell counts, identify any relationships with dipyrone dosage, therapy duration, and other factors. RESULTS: The mean age of the study population was 58.7 years, with a mean duration of dipyrone therapy of 6.5 years. Statistically significant decreases were observed in neutrophil, leukocyte, and platelet counts from baseline to follow-up; however, these reductions were not clinically relevant and within normal established laboratory reference values. No severe hematological or severe drug reaction such as agranulocytosis were observed. A limited multivariable model did not identify clinically meaningful associations between prescribed dipyrone dose or treatment duration and blood count changes. CONCLUSIONS: In this large cohort of chronic pain patients on long-term dipyrone therapy, only mild and clinically insignificant variations in hematological parameters were observed, and no cases of agranulocytosis were identified. However, the absence of an unexposed control group of chronic pain patients and the lack of systematic data on concomitant medications preclude attributing these observed changes to dipyrone alone.