Dapsone is an antibacterial sulfonamide with anti-inflammatory property, which showed therapeutic activity in patients with immune thrombocytopenia (ITP); the activity in patients who showed refractoriness to rituximab is unknown. We evaluated the effect of dapsone in 20 consecutive adult patients, median age 51 years, with primary ITP previously treated at least with steroids and rituximab. Median baseline platelet count was 19 × 10⁹/L, and the median interval between diagnosis of ITP and dapsone therapy was 46 months. Response (platelet count ≥ 30 × 10⁹/L) and complete response (CR; platelet count ≥ 100 × 10⁹/L) were 55 and 20%, respectively; median time to response (TTR) was 1 month. All responders were able to interrupt any other specific anti-ITP treatment. The median duration of dapsone therapy in responders and the median response duration were 31 and 42 months, respectively. None of responders lost response during treatment. One patient in CR interrupted dapsone after 9 months and still maintained the response after 48 months. None of the patients interrupted the treatment for toxicity. All the patients were screened for normal glucose-6-phosphate-dehydrogenase (G6PD); two patients showed mild increase of methemoglobin (MHb). These results highlight the therapeutic activity and good safety profile of dapsone in patients with ITP who previously failed rituximab treatment.
