In a 78-year-old male following hip replacement who has major depressive disorder with depressed mood, anorexia, and weight loss, what is the recommended first‑line antidepressant and initial dosing?

Recommended First-Line Antidepressant: Mirtazapine (Remeron)

For this 78-year-old male with major depressive disorder presenting with anorexia and weight loss following hip replacement, mirtazapine (Remeron) is the optimal first-line choice, starting at 7.5 mg at bedtime and titrating to 30 mg at bedtime as tolerated.

Rationale for Mirtazapine Selection

The clinical presentation of depression with prominent anorexia and weight loss makes mirtazapine uniquely suited for this patient. Mirtazapine is specifically noted to promote sleep, appetite, and weight gain—directly addressing this patient's core symptoms 1. In elderly patients, the medication is well-tolerated and potent 1.

Dosing Strategy

• Initial dose: 7.5 mg at bedtime
• Target dose: 30 mg at bedtime
• Titration: Gradual increase based on tolerability and response 1

Why Not the Other Options?

Bupropion (Wellbutrin)

• Activating properties make it inappropriate for elderly patients with anorexia
• Can worsen insomnia and should not be given after 3 PM 1
• Does not promote appetite or weight gain
• Better suited for apathetic depression without weight loss 1

Duloxetine (Cymbalta)

• Nausea is the most common adverse effect, which would be particularly problematic in a patient already experiencing anorexia 2
• Does not specifically promote appetite or weight gain
• Requires dose reduction in renal/hepatic disease 3

Fluoxetine (Prozac)

• Activating SSRI with very long half-life 1
• Should not be used in older adults due to greater risk of agitation and overstimulation 3
• Can worsen appetite and cause weight loss
• Side effects may not manifest for weeks due to long half-life 1

Venlafaxine

• Requires 2-4 weeks to titrate to efficacious dose (150-225 mg/day) 2
• Can cause blood pressure increases and cardiac conduction abnormalities—concerning in a 78-year-old post-surgical patient 2
• Does not specifically address appetite or weight concerns

General Principles for Elderly Patients

Start low, go slow: Older adults typically require approximately 50% of standard adult starting doses due to altered pharmacokinetics and increased sensitivity to adverse effects 3, 4. However, many eventually need the same maintenance doses as younger patients 4.

Monitoring Requirements

• Begin monitoring within 1-2 weeks of initiation 5
• Assess for suicidal ideation, agitation, irritability, or unusual behavioral changes 5
• Monitor weight, appetite, and sleep patterns given presenting symptoms
• Evaluate therapeutic response at 6-8 weeks; modify treatment if inadequate response 5

Expected Timeline

• Appetite improvement: May occur within 1-2 weeks
• Mood improvement: Typically requires 4-6 weeks
• Full response assessment: 6-8 weeks at therapeutic dose 5

Treatment Duration

Continue antidepressant for 4-9 months minimum after achieving satisfactory response for a first episode 5. Given this patient's age and post-surgical status, longer maintenance may be warranted to prevent recurrence 5.

Common Pitfalls to Avoid

• Do not use paroxetine in older adults—higher anticholinergic effects and sexual dysfunction 1, 3
• Avoid tertiary-amine TCAs (amitriptyline, imipramine) due to significant anticholinergic burden and cardiac risks in elderly patients 3
• Do not underdose—while starting low is appropriate, failure to titrate to therapeutic doses is a common cause of treatment failure
• Do not discontinue prematurely—weight restoration and full mood recovery take time

The evidence consistently supports that no second-generation antidepressant demonstrates superior efficacy over others 5, 6, making selection based on adverse effect profile, patient-specific symptoms, and comorbidities the appropriate strategy. In this case, mirtazapine's unique profile of promoting appetite and weight gain while treating depression makes it the clear first choice.