Mirtazapine-Induced Bicytopenia in a Patient With Multifactorial Delirium: A Case Report

Mirtazapine is often preferably used in geriatric patients with mood disorders due to its favourable side effects such as somnolence and weight gain. However, mirtazapine is associated with a rare but fatal side effect, agranulocytosis, which is not widely described. We present a case of mirtazapine-induced bicytopenia (moderate anaemia and leukopenia) in a geriatric patient. Notwithstanding scant available reports of mirtazapine-induced neutropenia, a case of iatrogenic anaemia from the drug is absent as per our literature review, although underreporting and undocumented cases are possibilities. We report a drug-induced bicytopenia in a 71-year-old Caucasian female patient, with a background of schizoaffective disorder, following mirtazapine use. The report shows declines in cell lines, 10 days after dose titration, complicated by SARS-CoV-2 infection and fever of unknown origin, with complete resolution of bicytopenia (moderate anaemia and leukopenia) following mirtazapine cessation. This was demonstrated by the definite temporal association displayed through the standardised Naranjo Adverse Drug Reaction Probability Scale. This case reports mirtazapine's rare side effects, anaemia and leukopenia and underscores the pharmacovigilance required in geriatric patients, who are prone to infections and complications of anaemia.