Mirtazapine

Key points

• The label indicates it for the treatment of major depressive disorder in adults.
• The boxed warning states antidepressants increased the risk of suicidal thoughts and behaviours in paediatric and young adult patients in short-term studies, and that all antidepressant-treated patients should be closely monitored for clinical worsening and emergence of suicidal thoughts and behaviours.
• It is not approved for use in paediatric patients.
• If sore throat, fever, stomatitis or signs of infection occur along with a low white blood cell count, treatment should be discontinued and the patient closely monitored.

How it works

Mirtazapine is an antidepressant with a different side effect profile from the SSRIs, notably its effects on appetite and sleep. The label records that it has been associated with increased appetite and weight gain, and that somnolence may impair judgment, thinking or motor skills. Those two effects are sometimes the reason it is chosen rather than reasons to avoid it, particularly where poor appetite and disturbed sleep are part of the presentation.

Safety specific to mirtazapine

Suicidal thoughts and behaviours. Antidepressants increased the risk of suicidal thoughts and behaviours in paediatric and young adult patients in short-term studies. The label directs close monitoring of all antidepressant-treated patients for clinical worsening and for emergence of suicidal thoughts and behaviours, and states that mirtazapine is not approved for use in paediatric patients.

Agranulocytosis. This is the instruction specific to mirtazapine. If sore throat, fever, stomatitis or signs of infection occur, along with a low white blood cell count, treatment should be discontinued and the patient closely monitored.

The practical consequence is unusual and worth stating plainly: on this medicine, an ordinary-seeming sore throat with fever is a reason to contact a prescriber and ask about a blood count, rather than something to treat as a passing infection.

Somnolence. Somnolence may impair judgment, thinking or motor skills, which matters for driving and for operating machinery, particularly when starting or after a dose increase.

Appetite and weight. Mirtazapine has been associated with increased appetite and weight gain.

When to seek urgent care

New or worsening suicidal thinking, or unusual changes in behaviour, need to reach the prescriber promptly. A sore throat with fever or mouth ulceration while taking mirtazapine warrants a blood count rather than watchful waiting.

Further reading

• DailyMed - REMERON- mirtazapine tablet, film coated
• Mirtazapine 15mg Tablets - Summary of Product Characteristics
• Mirtazapine: MedlinePlus Drug Information