What is the appropriate dosing regimen of mirtazapine (Remeron) for use as an appetite stimulant in adults?

Mirtazapine Dosing for Appetite Stimulation

For appetite stimulation in adults, start mirtazapine at 7.5 mg at bedtime and titrate to a maximum of 30 mg at bedtime based on response and tolerability.

Dosing Regimen

Initial Dose

• Start with 7.5 mg at bedtime 1
• This lower-than-standard dose minimizes sedation while providing appetite-stimulating effects 2
• The FDA-approved starting dose for depression is 15 mg, but lower doses are commonly used off-label for appetite stimulation 3

Dose Titration

• Increase to 15 mg at bedtime if appetite response is inadequate after 1-2 weeks 1
• Maximum dose: 30 mg at bedtime for appetite stimulation 1
• Dose changes should not occur more frequently than every 1-2 weeks due to mirtazapine's 20-40 hour half-life 3

Timing

• Administer at bedtime to leverage sedating effects and minimize daytime impairment 1
• Steady-state plasma levels are achieved within 5 days 3

Mechanism and Clinical Effects

How It Works

• Mirtazapine blocks presynaptic alpha-2 adrenergic receptors and antagonizes 5-HT2 and 5-HT3 receptors 4
• This mechanism promotes sleep, appetite, and weight gain 1
• The appetite-stimulating effect is particularly pronounced at lower doses (7.5-15 mg) 2

Expected Response

• Appetite improvement may occur within 4-6 days of initiating therapy 5
• In cancer patients with anorexia, mirtazapine significantly increased energy intake by 379.3 kcal after 4 weeks, with particular increases in protein (22.5 g), carbohydrates (43.4 g), and fats (13.2 g) 6
• The NCCN guidelines specifically note mirtazapine may be especially effective in patients with depression and anorexia 1

Special Populations

Elderly Patients

• Start with 7.5 mg at bedtime 1
• Oral clearance is reduced by 40% in elderly males and 10% in elderly females compared to younger adults 3
• Females exhibit significantly longer elimination half-lives (37 hours) compared to males (26 hours) across all ages 3

Renal Impairment

• Reduce dose by approximately 30% in moderate renal impairment (CrCl 11-39 mL/min) 3
• Reduce dose by approximately 50% in severe renal impairment (CrCl <10 mL/min) 3
• Start with 7.5 mg and titrate cautiously 3

Hepatic Impairment

• Reduce initial dose by approximately 30% due to decreased oral clearance 3
• Start with 7.5 mg at bedtime and monitor closely 3

Adverse Effects and Monitoring

Common Side Effects

• Sedation is the most common adverse effect, particularly at higher doses 7, 4
• Increased appetite and weight gain are expected therapeutic effects when used for appetite stimulation 1, 7
• Dizziness may occur 7
• Nightmares were reported more frequently at 2 weeks in one trial but resolved by 4-8 weeks 6

Safety Considerations

• Mirtazapine is well tolerated with minimal cardiovascular and anticholinergic effects 4
• The American Heart Association notes mirtazapine is safe in cardiovascular disease and offers additional benefits including appetite stimulation 1
• Transient elevations in cholesterol and liver function tests may occur 7

Clinical Context

Primary Indications for Appetite Stimulation

• Cancer-related anorexia and cachexia 1, 6
• Alzheimer's disease and dementia with poor appetite 1
• Palliative care settings where appetite loss impacts quality of life 1

Advantages Over Alternatives

• Unlike corticosteroids and progestational agents (megestrol acetate, medroxyprogesterone), mirtazapine addresses both appetite loss and commonly comorbid depression/anxiety 1
• Provides additional benefit for insomnia, which frequently coexists with appetite loss 1
• Better side effect profile than traditional appetite stimulants in cardiovascular disease 1

Important Caveats

• Lower doses (7.5 mg) minimize sedation while maintaining appetite-stimulating effects, making this the preferred starting point 2
• The appetite-stimulating effect appears most robust for fat intake, which provides concentrated energy for malnourished patients 6
• While appetite scores may not always show statistical improvement, actual energy intake increases significantly 6
• Mirtazapine should be discontinued gradually over several weeks rather than abruptly to avoid withdrawal symptoms 3
• Allow at least 14 days between discontinuing an MAOI and starting mirtazapine, and vice versa 3