Rx Update: April 2000

Mirtazapine

Mary Ross, R.Ph., M.B.A.
Peer Review Status: Internally Reviewed

Mirtazapine (Remeron® - Organon) is an antidepressant with a chemical structure unrelated to other currently available antidepressants. It is classified as a noradrenergic and specific serotonergic antidepressant (NaSSA). It has been shown to be as effective as tricyclic antidepressants (e.g., amitriptyline, desipramine, doxepin) and selective serotonin reuptake inhibitors (e.g., citalopram, fluoxetine, paroxetine) for the treatment of depression.

The most common adverse effects associated with the use of mirtazapine are somnolence, dizziness, dry mouth, increased appetite and weight gain. Mirtazapine has also been associated with increased cholesterol levels. It is metabolized by several CYP450 enzymes; however, in-vitro studies have shown that mirtazapine is not a potent inhibitor of CYP450 isoenzymes and no significant drug-drug interactions involving the CYP450 system have been reported. Agranulocytosis or severe neutropenia occurred in three patients during clinical trials. If a patient develops a sore throat, fever, stomatitis or signs of infection, along with a low WBC count, mirtazapine should be discontinued and the patient should be closely monitored. It is recommended that mirtazapine not be used in combination with a monoamine oxidase inhibitor (MAOI) or within 14 days of initiating or discontinuing MAOI therapy because there have been reports of serious, even fatal, reactions in patients receiving other antidepressants in combination with a MAOI.

Mirtazapine is available in 15 mg, 30 mg and 45 mg tablets. The recommended starting dose is 15 mg daily administered in a single dose at bedtime. Doses should be administered at bedtime to minimize daytime somnolence associated with mirtazapine. The usual effective dosage range is 15 to 45 mg daily. Dosage changes should not be made at intervals of less than one to two weeks in order to allow sufficient time for evaluation of therapeutic response. Caution should be used when administering mirtazapine to patients with compromised hepatic or renal function. Dose reductions may be necessary in these patients because of decreased clearance of mirtazapine.

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