Lay summary: The Pharmacovigilance of Mirtazapine: results of a prescription event monitoring study on 13,554 patients in England
Mirtazapine is an antidepressant (i.e. is used to treat depression). It is the first of a new type of antidepressant that works by altering levels of chemicals in the brain,
known as noradrenaline and serotonin. We monitored the safety of mirtazapine during its introduction into use in general practice in England.
The research method used is known as prescription-event monitoring (PEM). Patients prescribed mirtazapine were identified from dispensed prescriptions issued
between September 1997 and February 1999. A questionnaire was sent by the DSRU to the prescribing general practitioner (GP). This requested information on all
medical events that had occurred since mirtazapine was prescribed for that particular patient. A medical event is defined as any new illness, or change in an existing
illness, regardless of whether or not it was thought to be related to treatment. The information received was then analysed and used to monitor the safety of mirtazapine.
Information was collected for 13,554 patients prescribed mirtazapine. Drowsiness and loss of energy were the most frequently reported events. These were both more
likely to occur during the first month of treatment than during subsequent months. Some events that were reported during this study are already recognised as side-effects
of mirtazapine in the product literature. These events were abnormal liver function tests, fainting, abnormal behaviour and visual disturbance. However, some events that
were reported during this study were not previously recognised in product information as side-effects of mirtazapine i.e. agitation, aggression, rash, hallucinations and
abnormal dreams. A few events were reported as suspected adverse drug reactions (i.e. the reporting GP suspected that the event had possibly been caused by mirtazapine),
the most serious of which were facial swelling (5 reports), allergy (3 reports) and abnormal bone marrow cells (3 reports).