Shirmila Syamala^1,, Hanadi Khamis Mubarak Alhamad¹, Essa Al-Sulaiti¹, Asma Mirghani Sayed Abbas¹

Introduction: Mirtazapine is an antidepressant commonly used and considered safe in the elderly. It is favored in elderly patients suffering from insomnia and weight loss secondary to depression. Here, we present a case where mirtazapine caused an unexpected adverse effect of agitation and hallucinations contrary to the expected reaction of sedation. Case Presentation: An 86 year old female was admitted with complaints of poor oral intake. She was very frail and weighed 23 kilos. She was malnourished and suffering from hypoalbuminemia and electrolyte abnormalities. Her evaluation did not reveal an organic cause for weight loss. Her cognition was intact. She was started on mirtazapine 7.5 mg for depression and received 2 doses. During the second night, she was unable to sleep and started having visual hallucinations. The hallucinations were described as people in the wall, boxes, and cars coming from the window to hit her. Subsequently Mirtazapine was discontinued and hallucinations stopped 48 hours after the last dose. Discussion: Mirtazapine is a tetracyclic antidepressant with serotonergic and noradrenergic activity. Mirtazapine has been shown to be very effective in treating depression in elderly. The decision to treat with mirtazapine is also based on its side effect profile. Somnolence happens in 50 % of people and weight gain in 15% of patients. Therefore mirtazapine is commonly used to treat depression in patients with concomitant insomnia and anorexia. The relative tolerability of mirtazapine makes it a first-line medication for many elderly with major depression. Peak plasma concentrations are reached within 2.2 to 3.1 hours after single oral doses of 15 to 75mg. Mirtazapine is extensively metabolized in the liver. Protein binding is 85%. Mean elimination half-life is 22 hours, so it can be administered once a day. Despite its known sedative effect, there have been reports of visual and auditory hallucinations and insomnia occurring with the use of mirtazapine, which could be related to increase in dopamine levels in the frontal cortex. Our patient was elderly, frail and malnourished. Her hypoalbuminemia related to malnutrition and low protein binding could also be a factor as increased free drug will be available to enter the CNS. Although she was started at half the adult dose, it may still have been high for her due to her low weight. Per the Naranjo criteria, Mirtazapine was determined as the probable cause of hallucination in this case. This case illustrates that although Mirtazapine is a relatively safe drug to use in elderly, we need to be cautious when starting the drug or increasing the dose, especially in malnourished patients.

Mirtazapine, elderly, adverse effect, hallucinations, malnourished