Can Fluvoxamine (Luvox) and Mirtazapine (Remeron) Be Used Together?
Yes, fluvoxamine and mirtazapine can be combined for treatment-resistant depression, but this combination requires significant dose reduction of mirtazapine (by 50-75%) due to a major pharmacokinetic interaction, and close monitoring for serotonin syndrome and excessive sedation.
The Critical Drug Interaction
Fluvoxamine causes a 3-4 fold increase in mirtazapine blood levels 1. This occurs because fluvoxamine is a potent inhibitor of CYP1A2, CYP2D6, and CYP3A4—the same enzymes that metabolize mirtazapine 2. This is not a theoretical concern; documented cases show mirtazapine levels tripling when fluvoxamine 100 mg/day was added, and quadrupling with fluvoxamine 50 mg/day 1.
Dosing Strategy
Starting the Combination:
- If adding fluvoxamine to existing mirtazapine: Reduce mirtazapine dose by 50-75% when initiating fluvoxamine
- If adding mirtazapine to existing fluvoxamine: Start mirtazapine at 7.5 mg daily (half the usual starting dose)
- Fluvoxamine dosing: Start at 50 mg daily, can increase to 100-150 mg daily for optimal antidepressant effect 3, 4
- Mirtazapine target: With the interaction, 7.5-15 mg mirtazapine will achieve therapeutic levels equivalent to 30-60 mg when given alone
Rationale for Combination:
The evidence supports augmentation strategies when first-line antidepressants fail. Augmenting an SSRI (like fluvoxamine) with mirtazapine showed similar efficacy to switching strategies in treatment-resistant depression 5. Two trials with 1,231 participants found no difference between switching to mirtazapine versus augmenting with mirtazapine 5.
Safety Monitoring Requirements
Week 1-2 (Critical Period):
- Serotonin syndrome surveillance: Monitor for agitation, confusion, tremor, hyperthermia, muscle rigidity, autonomic instability 2
- Excessive sedation: Both drugs cause somnolence; the combination amplifies this effect
- Suicidality assessment: Required for all antidepressant initiations, especially in first 1-2 weeks 6
Ongoing Monitoring:
- Weight and appetite: Mirtazapine commonly causes increased appetite and weight gain 2
- Blood pressure: Monitor for orthostatic hypotension
- Complete blood count: Mirtazapine carries rare risk of agranulocytosis; if fever, sore throat, or infection develops with low WBC, discontinue immediately 2
- Liver function tests: Both drugs can elevate transaminases 2
Clinical Advantages of This Combination
This pairing offers complementary mechanisms:
- Fluvoxamine: SSRI action on serotonin reuptake
- Mirtazapine: Enhances noradrenergic and serotonergic neurotransmission through alpha-2 antagonism, blocks 5-HT2 and 5-HT3 receptors 7
Mirtazapine specifically improves sleep and anxiety symptoms associated with depression 2, 8, which can be beneficial if these are prominent features. One study showed mirtazapine superior to fluoxetine for sleep quality in severely depressed patients 8.
Common Pitfalls to Avoid
- Using standard mirtazapine doses: This will result in toxic levels, excessive sedation, and increased adverse effects
- Inadequate serotonin syndrome monitoring: The combination of two serotonergic agents increases this risk 2
- Ignoring sedation: Warn patients about additive sedation effects; advise against driving or operating machinery until tolerance develops 2
- Premature discontinuation: If stopping either medication, taper gradually to avoid withdrawal symptoms 2
Alternative Considerations
If the interaction management seems too complex, augmentation with bupropion or cognitive therapy showed similar efficacy to other augmentation strategies in the STAR*D trial 5. These alternatives avoid the pharmacokinetic interaction entirely.
Duration of Treatment
Once remission is achieved, continue combination therapy for 4-9 months minimum for first episode depression 6. For patients with 2+ prior episodes, longer maintenance treatment is beneficial 6.