Does Fluvoxamine Cause Bradycardia?
Yes, fluvoxamine can cause bradycardia, though this is typically a mild and clinically insignificant effect in most patients. The bradycardia is generally moderate, requires no treatment when occurring with therapeutic doses, and represents a statistically but not clinically significant slowing of heart rate 1.
Evidence from FDA Drug Labeling and Overdose Data
The FDA drug label for fluvoxamine explicitly documents bradycardia as an adverse effect 2. In overdose situations, bradycardia has been observed with doses below 1000 mg and was consistently moderate, requiring no treatment 3. The label also specifically warns about bradycardia when fluvoxamine is co-administered with diltiazem 2, and notes that one case of bradycardia and hypotension occurred with co-administration of fluvoxamine and metoprolol 2.
Clinical Significance in Therapeutic Dosing
In therapeutic doses, fluvoxamine's effect on heart rate is minimal and not clinically concerning 1. A controlled study comparing fluvoxamine to maprotiline in 33 depressed patients found that fluvoxamine caused no significant changes in ECG parameters, with only a nonsignificant trend toward lower heart rate 4. This contrasts sharply with tricyclic antidepressants, which cause clinically significant heart rate increases and conduction abnormalities 1.
The research demonstrates that fluvoxamine has no anticholinergic or quinidine-like properties that characterize tricyclic antidepressants, and its cardiac effects are limited to this mild heart rate slowing 1.
Key Drug Interactions That Increase Bradycardia Risk
Exercise extreme caution when combining fluvoxamine with:
Beta-blockers: Fluvoxamine increases propranolol levels 5-fold (range 2-17 fold), causing potentiation of heart rate reduction 2. One case each of bradycardia/hypotension with metoprolol and orthostatic hypotension have been reported 2. Reduce the initial beta-blocker dose and use more cautious titration when co-administering 2.
Diltiazem: Bradycardia has been specifically reported with this combination 2.
Tizanidine: This combination is contraindicated due to significant hypotension, bradycardia, and sedation risk 5.
Clinical Context and Management
The bradycardia from fluvoxamine alone is rarely a clinical problem. The 2018 ACC/AHA/HRS Bradycardia Guidelines emphasize that treatment should not be prescribed solely based on heart rate below an arbitrary cutoff—symptoms are the critical component 6, 7, 8.
If symptomatic bradycardia develops:
- First assess for reversible causes, particularly drug interactions 6, 7
- Consider dose reduction or discontinuation if fluvoxamine is not essential 6
- Evaluate for concomitant medications that slow heart rate (beta-blockers, calcium channel blockers, digoxin, antiarrhythmics) 6, 7
- Permanent pacing is only indicated if symptomatic bradycardia persists despite addressing reversible causes and the medication cannot be discontinued 6
Common Pitfalls to Avoid
- Do not assume all SSRIs have identical cardiac profiles—fluvoxamine's bradycardic effect distinguishes it from other SSRIs that may cause tachycardia in serotonin syndrome 9
- Do not overlook drug-drug interactions, particularly with CYP1A2 substrates like tizanidine (contraindicated) and beta-blockers (require dose adjustment) 9, 5, 2
- Do not confuse the mild bradycardia from therapeutic dosing with the more concerning cardiac effects in massive overdose, where ECG abnormalities including heart arrest, QT prolongation, and AV block can occur 2
Bottom line: Fluvoxamine causes mild bradycardia that is rarely clinically significant when used alone at therapeutic doses, but becomes concerning when combined with other rate-lowering medications, particularly beta-blockers and calcium channel blockers.