Fluvoxamine

Fluvoxamine is a selective serotonin reuptake inhibitor (SSRI) commonly prescribed under the brand name Luvox. It is an oral antidepressant designed to help regulate mood by increasing serotonin availability in the brain.

It's FDA-approved for obsessive-compulsive disorder (OCD) and is also used off-label for depression and certain anxiety disorders.

Fluvoxamine blocks the serotonin transporter (SERT), which keeps more serotonin available between nerve cells. That's the basis for its effect on OCD and mood.

The key gene affecting fluvoxamine metabolism is CYP2D6, which encodes an enzyme in the liver responsible for processing many medications. Variants in CYP2D6 produce different metabolizer phenotypes—ranging from poor to ultrarapid—based on how active the enzyme is.

These genetic differences can alter how quickly fluvoxamine is cleared from the body. Poor metabolizers have reduced enzyme activity leading to slower clearance and higher drug exposure, while ultrarapid metabolizers break down the drug more quickly, potentially reducing its effectiveness.

CYP2D6 phenotype groups influence fluvoxamine exposure and risk profile: poor metabolizers may have increased drug levels and greater side‐effect risk, ultrarapid metabolizers may clear the drug too fast to achieve benefit, and intermediate or normal metabolizers fall between these extremes, guiding dose selection and monitoring.

Genetic variations in CYP2D6 influence fluvoxamine processing, altering drug exposure and side effect risk as follows:

Ultrarapid Metabolizer

• Effect on drug levels: Decreased drug levels due to rapid metabolism.
• Clinical consequence: Potential reduced efficacy and insufficient symptom control.
• Side effects: Lower incidence of common SSRI side effects (e.g., nausea); severity and frequency not well established.

Normal Metabolizer

• Effect on drug levels: Expected drug levels under standard dosing.
• Clinical consequence: Typical therapeutic response at recommended doses.
• Side effects: Common mild to moderate effects such as gastrointestinal upset or insomnia.

Intermediate Metabolizer

• Effect on drug levels: Slightly increased drug levels due to reduced metabolism.
• Clinical consequence: Increased risk of side effects without dose adjustment.
• Side effects: More frequent mild to moderate effects like nausea or drowsiness.

Poor Metabolizer

• Effect on drug levels: Markedly increased drug levels from greatly reduced metabolism.
• Clinical consequence: Heightened risk of adverse effects at standard doses.
• Side effects: More severe or frequent events (e.g., sedation, nausea, potential for serotonin syndrome).

Indeterminate/Not Available

• Effect on drug levels: Unknown.
• Clinical consequence: No specific guidance; follow standard dosing with clinical monitoring.
• Side effects: Unknown.

CYP2D6 Dosing Guideline

Examples from the CPIC guidelines: for CYP2D6 poor metabolizers, consider alternative antidepressants not predominantly metabolized by CYP2D6 such as sertraline or escitalopram. These are examples only and not a substitute for professional medical advice.

• CPIC – CPIC guideline for SSRI and SNRI antidepressants

Learn more about how genetics may affect your response to Fluvoxamine and related medications:

• Antidepressant Not Working? What to Know Before You Give Up
• Anxiety Medication Not Working? Genetics May Be Part of the Problem
• Escitalopram Not Working? Why Lexapro Might Not Be Helping
• Paroxetine Side Effects: Why Paxil Hits Some People Harder
• Sertraline Not Working? Here's What Might Be Going On