What muscle relaxer can be safely prescribed with fluvoxamine (Luvox)?

Muscle Relaxants That Can Be Safely Prescribed with Fluvoxamine

Baclofen is the safest muscle relaxant to prescribe for patients taking fluvoxamine, as it does not have significant interactions with this SSRI medication. 1

Understanding Fluvoxamine Drug Interactions

Fluvoxamine is a selective serotonin reuptake inhibitor (SSRI) that is a potent inhibitor of cytochrome P450 enzymes, particularly:

• Strong inhibitor of CYP1A2 2
• Moderate inhibitor of CYP2C19 and CYP3A4 3
• Weak inhibitor of CYP2D6 4

These enzyme inhibition properties create significant drug interaction concerns with several muscle relaxants:

• Tizanidine is contraindicated with fluvoxamine due to potentially dangerous interactions 2
• Benzodiazepines (especially those metabolized by hepatic oxidation like diazepam) should generally be avoided due to significantly reduced clearance and potential for substantial accumulation 2

Safe Muscle Relaxant Options with Fluvoxamine

Baclofen

• Recommended as first-line choice for patients on fluvoxamine 1
• Metabolized primarily by deamination, not significantly affected by CYP450 inhibition 1
• Standard dosing can be used (starting with 5-10mg three times daily) 1
• Should not be discontinued abruptly due to risk of withdrawal symptoms 1

Cyclobenzaprine (Second-line option)

• Can be considered if baclofen is not effective or not tolerated 5
• Use with caution and at lower doses (starting at 5mg) due to potential for increased sedation 5
• Monitor for anticholinergic side effects (confusion, constipation, urinary retention) 5

Muscle Relaxants to Avoid with Fluvoxamine

Tizanidine (Contraindicated)

• Absolutely contraindicated with fluvoxamine 2
• Fluvoxamine significantly reduces tizanidine clearance by inhibiting CYP1A2 6
• Co-administration can lead to dangerous hypotension, bradycardia, and excessive sedation 6

Benzodiazepines (Use with extreme caution)

• Alprazolam: If absolutely necessary, initial dose should be at least halved due to 50% reduction in clearance and doubled plasma concentrations when combined with fluvoxamine 2
• Diazepam: Co-administration is generally not advisable; clearance reduced by 65% 2
• Increased risk of respiratory depression when benzodiazepines are combined with other CNS depressants 1

Special Considerations

• Elderly patients: Require dose reductions of muscle relaxants due to reduced clearance 6
• Hepatic/renal dysfunction: Further increases risk of adverse effects with muscle relaxants 6
• Monitoring: Watch for signs of excessive sedation, respiratory depression, or hypotension 1
• Avoid co-prescribing opioids: The combination of muscle relaxants, SSRIs, and opioids significantly increases risk of respiratory depression 1

Practical Prescribing Algorithm

1. First-line: Baclofen starting at 5mg three times daily, titrate as needed up to 20mg three times daily 1
2. If ineffective: Consider cyclobenzaprine at reduced starting dose (5mg) 5
3. Avoid tizanidine completely 2
4. Avoid benzodiazepine muscle relaxants unless absolutely necessary, and then use at significantly reduced doses with careful monitoring 2

Remember that the risk of adverse effects increases with polypharmacy, particularly when combining medications that affect the central nervous system. Always use the lowest effective dose for the shortest duration necessary.