Starting Dose of Mirtazapine
Start mirtazapine at 15 mg once daily at bedtime. 1
Dosing Algorithm
Initial Dosing
- Begin with 15 mg once daily, administered in the evening prior to sleep 1
- This is the FDA-approved starting dose and is supported by multiple clinical guidelines 2
- The 15 mg starting dose balances efficacy with tolerability, as lower doses (7.5 mg) are associated with increased sedation 2
Titration Strategy
- If inadequate response after 1-2 weeks at 15 mg, increase to 30 mg daily 1
- Maximum dose is 45 mg daily 1
- Do not make dose changes more frequently than every 1-2 weeks to allow sufficient time to evaluate response 1
Special Considerations for This Patient
Context-Specific Factors
Depression with Anxiety: Mirtazapine is particularly well-suited for patients with comorbid anxiety, as it has demonstrated beneficial anxiolytic effects 2, 3, 4
History of Eating Disorders: This requires careful consideration:
- Mirtazapine promotes appetite and weight gain 2
- In patients with a history of restrictive eating disorders who are weight-restored, this may be acceptable
- However, in patients with active concerns about weight or body image, this side effect profile may be problematic
- The 2023 APA Eating Disorders guideline recommends fluoxetine 60 mg daily for bulimia nervosa 2, but does not specifically address mirtazapine use
Concurrent Fluoxetine Use:
- There are no absolute contraindications to combining mirtazapine with fluoxetine 1
- This combination may provide complementary mechanisms of action
- Monitor for serotonin syndrome, though risk is lower with mirtazapine than with other combinations 1
- No specific dose adjustments are required for this combination 1
Age-Related Dosing (59-Year-Old Patient)
- Standard adult dosing applies - start at 15 mg daily 1
- While older adults (typically defined as ≥65 years) may require lower starting doses, a 59-year-old patient should receive standard adult dosing unless other factors (renal/hepatic impairment) are present 2
Dose Modifications
Drug Interactions Requiring Adjustment
- Strong CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin): May require dose reduction 1
- Strong CYP3A4 inducers (e.g., carbamazepine, phenytoin): May require dose increase 1
- Cimetidine: May require dose reduction 1
Organ Dysfunction
- Hepatic impairment: Consider dose reduction and careful titration 1, 3
- Renal impairment: Consider dose reduction and careful titration 1, 3
Clinical Advantages in This Patient
Rapid Onset: Mirtazapine may demonstrate earlier response than SSRIs, with significant improvements noted as early as 1 week 2, 5, 6, 7
Sleep Benefits: The sedating properties at bedtime dosing can improve sleep disturbances commonly associated with depression 2, 4
Anxiety Management: Dual enhancement of noradrenergic and serotonergic neurotransmission provides anxiolytic effects 2, 4
Critical Monitoring
Screen for bipolar disorder before initiating treatment, as antidepressants can precipitate manic episodes 1
Monitor for agranulocytosis: Though rare, reversible severe neutropenia has been reported; consider baseline CBC and monitoring if fever, sore throat, or other signs of infection develop 5, 6
Weight monitoring: Given the eating disorder history, regular weight checks are essential 2
Discontinuation: If stopping mirtazapine, taper gradually rather than stopping abruptly to minimize withdrawal symptoms 1