Oseltamivir, a neuraminidase inhibitor, plays a key role in the management of influenza. The most commonly reported adverse effect of oseltamivir is gastrointestinal discomfort including nausea and vomiting.1,2 Here we report a case of enterorrhagia, a rare and neglected adverse effect after oseltamivir use.

A twelve year old boy was at day four of empiric treatment for Influenza infection and began to experience hematochezia. His mother brings him to the Emergency Department reporting four episodes of anal bleeding. Physical examination was normal and there were no signs of hemodynamic commitment. Laboratorial screening was performed and no abnormalities were seen. Hematocrit was 43.1%, hemoglobin 14.8g/dL (NR: 13.5–17.5g/dL), platelets 175,000 (NR: 150,000–450,000), RNI 1.14 and creatinine 0.84 (NR: 0.5–1.5). The child had no prior history of diseases, surgery or medication use and had a proper development to his age. The treatment was suspended, hematochezia ceded and the patient was full recovered.

Brazil is experimenting a rise in the incidence of influenza cases. In 2015, 30% of flu syndromes were caused by influenza virus with 1.8% of influenza A(H1N1)pdm09. This year however, influenza virus is responsible for 78.5% of flu syndrome and influenza A(H1N1)pdm09 for 70.9% of them.3,4 This data makes the clinician alert to the problem and prompt to prescribe oseltamivir when facing a flu syndrome.

We are aware of controversial on the literature about the efficacy of oseltamivir.5 In a developing country scenario, confirmatory tests for H1N1 are not available everywhere. The clinician must be aware of adverse events and consider the risk-benefit of treatment before prescription.