Dapsone response in immune thrombocytopenic purpura is associated with dapsone dose and mediated through reduction in haemoglobin: A longitudinal data analysis of 58 adult and paediatric ITP patients demonstrates efficacy and safety.

Despite several studies reporting the effectiveness of dapsone in immune thrombocytopenic purpura (ITP), information on its mechanism of action, dose-response relationship and response predictors remains limited. To address this knowledge gap, we analysed 433 healthcare visit data of 58 ITP patients (29 males and 29 females; 39 adults and 19 paediatric) treated with dapsone (mean: 1.19 mg/kg/day) after 0-4 prior treatments. Among them, 14 had newly diagnosed, 23 had persistent and 21 had chronic ITP. The median ages for paediatric and adult patients were 6.4 and 40.9 years respectively. Median response time, response duration and follow-up period were 40, 151 and 142 days respectively. The overall response rate was 58.6%, of which 94.1% of patients responded within 6 months and 44.8% (n = 26) maintained a response at the last follow-up. Mediation analysis showed that the association between dapsone and responses was mediated via haemoglobin reduction. Response rates were 5.38 times higher in patients who experienced a reduction in haemoglobin than in those who did not experience a reduction in haemoglobin (p = 0.008). Age, sex, previous treatment numbers and response, ITP types, baseline platelets and concurrent treatments were not associated with a response. Two patients needed dapsone discontinuation due to adverse events.