Introduction Anaemia, leucopenia and thrombocytopenia have been rarely reported in patients receiving methylphenidate. There is no recommendation for routine blood testing unless clinically indicated. We report two children who developed reversible neutropenia on treatment with methylphenidate.

Method-case reports Case1: Routine blood test in a 14 year old boy with ADHD on Concerta XL 54 mg daily showed significant neutropenia (white cell count (WCC) - 3.1, neutrophil count - 0.8). The drug was discontinued following which WCC and neutrophil counts increased. Concerta was restarted but count started to decline after 2 weeks. Hence the drug was stopped. Since then, his counts have remained normal.

Case 2: Routine blood test in a 12 year old boy with ADHD on concerta XL 36 mg and 10 mg of methylphenidate immediate release daily showed neutropenia (1.72). The count was further reduced to 1.55 after a month. There was no history of any viral infection during or immediately before this period. Neutrophil count normalised 1 month after stopping medication.

Discussion Methylphenidate is the most commonly prescribed stimulant for ADHD. There are wide variation in haematological monitoring. A literature review indicates that previous clinical trials have failed to demonstrate statistically significant occurrence of serious haematological abnormalities. Our experience shows that neutropenia can indeed be a serious side effect. In both cases, prompt reversal of neutropenia was observed upon discontinuation. Given the cost and discomfort associated with routine investigations, we recommend large multicentric observation studies with the aim of creating a unified standard.