Nifurtimox therapy for Chagas disease does not cause hypersensitivity reactions in patients with such previous adverse reactions during benznidazole treatment.

Currently, only two drugs are approved for treating Trypanosoma cruzi infection: benznidazole and nifurtimox. Adverse reactions are frequent with both drugs: they have chemical similarities and common metabolic pathways making cross reactions a possibility. Our objective was to describe the safety/tolerability profile of nifurtimox in patients who had previously discontinued benznidazole due to hypersensitivity reactions. We performed a prospective observational study from September 2009 to December 2011. Patients who discontinued benznidazole therapy due to hypersensitivity reactions (HR) and were later treated with nifurtimox were included. HR to benznidazole were defined as presence of a rash with or without mucosal involvement, fever or laboratory abnormalities (such as eosinophilia, leucopaenia or impaired liver function tests). The drugs were prescribed for 60 days (benznidazole) or 60-90 days (nifurtimox). The National Cancer Institute criteria (CTCAE, 2006, Version 3.0) were used for grading and reporting of adverse reactions (AR). Eighteen patients (16 females, two males, median age 35.5 years, range 15-50 years) with asymptomatic late chronic infection, were included. Median time between benznidazole interruption and start of therapy with nifurtimox was 121.5 days (IQR 72-223 days). Fifteen patients (83.3%) developed an AR to nifurtimox, gastrointestinal complaints and anorexia being the most common, and 13 patients (72%) completed the treatment schedule. Five patients interrupted therapy (27.8%) mainly because of gastrointestinal intolerance and/or nervous system toxicity. Only one patient developed skin lesions, a mild maculopapular rash not requiring specific therapy or treatment withdrawal. There was no severe AR. Nifurtimox as second line therapy in patients who discontinued benznidazole specifically due to HR appears to be safe and does not seem to be associated with a higher incidence of AR.