mirtazapine: clinical use

Prescribing considerations

• Licensed for adults with episodes of major depression; selected products advise against use in people under 18 because efficacy was not demonstrated and safety concerns exist.
• Assess suicide and self-harm risk and monitor clinical worsening, unusual behaviour and suicidality, especially early in treatment and after treatment changes.
• Review renal and hepatic function because impaired clearance can increase exposure.
• Use caution with seizure disorders, bipolar disorder or previous mania, psychosis, diabetes, hypotension, glaucoma, urinary retention and cardiovascular or QT-risk factors.
• Avoid abrupt withdrawal; plan gradual discontinuation.
• Consider excipients and swallowing needs when selecting a formulation.

Contraindications and cautions

• Hypersensitivity to mirtazapine or a formulation excipient.
• Concomitant use with a monoamine oxidase inhibitor.
• Oral solution is unsuitable in hereditary fructose intolerance because it contains maltitol; tablet excipient restrictions vary by product.

Monitoring

• Mood, response, adherence, suicidal thoughts and behavioural change.
• Sedation, dizziness, falls risk, appetite and weight.
• Blood glucose control in people with diabetes.
• Serum sodium when symptoms or risk factors suggest hyponatraemia.
• Full blood count if signs of infection occur.
• Manic symptoms, seizures and akathisia.
• ECG and electrolytes when clinically indicated by cardiac disease, overdose, QT-risk factors or interacting medicines.
• Liver function when symptoms suggest hepatic injury.

Clinical pharmacology

Mirtazapine enhances central noradrenergic and serotonergic transmission through presynaptic alpha-2 antagonism. It blocks 5-HT2, 5-HT3 and H1 receptors, with H1 antagonism contributing to sedation. It is well absorbed orally, extensively metabolised through pathways involving CYP enzymes, and eliminated in urine and faeces; clearance may fall with renal or hepatic impairment.

Formulation and product differences

• Film-coated tablets should be swallowed whole and may contain lactose, depending on the product.
• Orodispersible tablets disintegrate on the tongue and can be swallowed without water; the selected product contains lactose, sorbitol and aspartame.
• Oral solution is measured with the supplied syringe and may be swallowed directly or mixed with water. It contains maltitol and sodium benzoate.
• Slight pharmacokinetic differences exist between tablets and oral solution; exercise care when switching formulations.

Dispersible tablet

Route: Oral

Strengths: 15 mg, 30 mg, 45 mg

Oral solution

Route: Oral

Strengths: 15 mg/mL