Mirtazapine
Class: antidepressant – central presynaptic alpha 2 and 5HT antagonist
Indications (NB some may be unlicensed): major depression, nausea; pruritis in palliative care
Contraindications/cautions: bipolar depression, epilepsy, cardiac disease, prostatic hypertrophy, diabetes, abrupt withdrawal
Adverse reactions: common: increased appetite, weight gain, drowsiness in first few weeks of treatment, dizziness, headache, dry mouth; less common: convulsions, tremor, nightmares, mania, syncope, hyponatraemia, nausea
Metabolism/clearance: metabolised by metabolising enzyme CYP2D6, 1A2 and 3A mainly in the liver to at least one active metabolite (by CYP3A)
Interactions:
- increased clinical effect/toxicity of mirtazapine (due to increased blood concentrations of parent) may occur with some CYP metabolising enzyme inhibitors (see above) e.g. bupropion, aprepitant, ciprofloxacin, clarithromycin, fluconazole, fluoxetine, grapefruit juice, itraconazole, ketoconazole, paroxetine, quinine
- decreased clinical effect/toxicity of mirtazapine (due to decreased blood concentrations of parent) may occur with some CYP metabolism enzyme inducers (see above) e.g. broccoli, carbamazepine, dexamethasone, phenobarbitone, phenytoin, prednisone, rifampicin, smoking, St John’s wort
- additive risk of serotonin syndrome (potentially fatal syndrome – symptoms include sweating, diarrhoea, confusion) with other serotonergic drugs e.g. amitriptyline, carbamazepine, fluoxetine, paroxetine, tramadol, lithium
| Dosing: | |
|---|---|
| oral: | 15 to 45 mg at bed-time (start with 15 mg and increase slowly) |
| subcut: | not available |
Syringe driver: not available
Mechanism of action: blocks presynaptic alpha 2 and 5HT 2 and 3 receptors increasing central noradrenaline and serotonin (blocking 5HT 2 and 5HT 3 receptors allowing stimulation of 5HT 1 receptors)
Peak concentrations: oral: 2 hours Half life: 20 to 40 hours