The pharmacovigilance of mirtazapine
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).