Analysis of a child who developed abnormal neuropsychiatric symptoms after administration of oseltamivir: a case report

BACKGROUND Neuropsychiatric side effects of oseltamivir occur occasionally, especially in infants and young patients, but nothing is known about possible contributory factors. CASE PRESENTATION We report a case of a 15-year-old Japanese female with influenza infection who developed abnormal psychiatric symptoms after administration of standard doses of oseltamivir. She had no history of neurological illness, had never previously taken oseltamivir, and had not developed psychiatric reactions during previous influenza infection. Her delirium-like symptoms, including insomnia, visual hallucinations, and a long-term memory deficit, disappeared after cessation of oseltamivir and administration of benzodiazepine. Detailed assessment was performed, including neurological examination (electroencephalogram, brain magnetic resonance imaging, single photon emission computed tomography with 99mTc-ethyl cysteinate dimer and with (123)I-iomazenil, cerebrospinal fluid analysis and glutamate receptor autoantibodies), drug level determination and simulation, and genetic assessment (OAT1, OAT3, CES1, Neu2). CONCLUSIONS Abnormal slowing in the electroencephalogram, which is characteristic of influenza-associated encephalopathy, was not observed in repeated recordings. The serum level determination of active metabolite Ro 64-0802 determined at 154 h after final dosing of oseltamivir was higher than the expected value, suggesting delayed elimination of Ro 64-0802. Thus, abnormal exposure to Ro 64-0802 might have contributed, at least in part, to the development of neuropsychiatric symptoms in this patient. The score on Naranjo's adverse drug reaction probability scale was 6. Mutation of c.122G > A (R41Q) in the sialidase Neu2 gene, increased CSF glutamate receptor autoantibodies, and limbic GABAergic dysfunction indicated by SPECT with (123)I-iomazenil were found as possible contributory factors to the CNS side effects.