Safety of mirtazapine: a review

The clinical trial development programme of mirtazapine (Org 3770), performed in Europe and the United States, demonstrated an outstanding safety profile of this compound. The evaluation of the safety was based on data from all patients who took at least one dose of study medication during studies comparing mirtazapine with placebo, amitriptyline or other active comparators. A general indication of mirtazapine's safety is the significantly lower percentage of patients (65%) who complained of any adverse clinical experiences compared with the placebo- (76%) or amitriptyline-treated group (87%). Moreover, drop-out rates due to adverse clinical experiences were significantly lower than in the amitriptyline-treatment group. Mirtazapine has virtually no anticholinergic, adrenergic or typical selective serotonin reuptake inhibitor (SSRI) side effects. The only significantly higher incidences versus placebo were seen in the adverse clinical effects of drowsiness (23% versus 14%), excessive sedation (19% versus 5%), dry mouth (25% versus 16%), increased appetite (11% versus 2%) and weight increase (10% versus 1%). These complaints were typically mild and transient in nature, and decreased over time despite increased doses of mirtazapine. In contrast, significantly higher incidences of headache (5% versus 10%) and weight decrease (2% versus 6%), symptoms commonly seen in depressed patients, were recorded in the placebo-treated patients. Also, typical SSRI adverse events, such as nausea, vomiting, diarrhoea and insomnia, and symptoms of sexual dysfunction were registered less frequently in mirtazapine-treated patients than in the placebo-treated patients. Approximately 10% of the mirtazapine-treated patients in the clinical trial programme were older than 65 years. The pattern of adverse clinical experiences seen in this group of patients is fully in line with that seen in the overall patient population. The analysis of vital sign indices, i.e. blood pressure and heart rate, showed that no changes occurred with mirtazapine treatment; this pattern was fully comparable to that seen with placebo. Furthermore, very low incidences of clinically relevant changes in laboratory indices, such as the liver enzymes alanine aminotransferase and aspartate aminotransferase or neutropenia, were recorded in each treatment group. Mirtazapine has a very low seizure-inducing potential: only one case was recorded in a patient with a history of seizures during previous treatment with clomipramine. The low seizure-inducing potential combined with a lack of cardiotoxic properties allows safety in an overdose of mirtazapine, even in elderly patients. The only symptom seen in the patients taking an overdose of mirtazapine alone or in combination with other drugs was excessive but transient somnolence, which resolved spontaneously within a few hours. In conclusion, the new antidepressant mirtazapine offers clinicians a unique combination of strong efficacy and good safety.