Can Flexeril (cyclobenzaprine) affect heart rhythm?

Can Flexeril (Cyclobenzaprine) Affect Heart Rhythm?

Yes, Flexeril (cyclobenzaprine) can affect heart rhythm due to its structural similarity to tricyclic antidepressants, which are known to cause arrhythmias, sinus tachycardia, and prolongation of cardiac conduction time. 1

Mechanism of Cardiac Effects

Cyclobenzaprine's cardiac effects stem from its pharmacological profile:

• Structurally related to tricyclic antidepressants (TCAs) like amitriptyline and imipramine 1
• Causes "slight to moderate increase in heart rate in animals" according to FDA labeling 1
• Has anticholinergic effects that can influence cardiac conduction 1
• FDA labeling specifically warns that "tricyclic antidepressants have been reported to produce arrhythmias, sinus tachycardia, prolongation of the conduction time leading to myocardial infarction and stroke" 1

Risk Factors for Cardiac Effects

The risk of cardiac rhythm disturbances with cyclobenzaprine is higher in:

• Elderly patients (≥65 years) who have approximately 1.7-fold higher plasma concentrations 1
• Patients with hepatic impairment who have approximately double the plasma concentration values 1
• Patients taking other medications that affect heart rhythm or serotonergic pathways 1, 2

Drug Interactions Affecting Cardiac Function

Cyclobenzaprine can have dangerous interactions with:

• Serotonergic medications (SSRIs, SNRIs, TCAs, tramadol, bupropion) potentially causing serotonin syndrome 1, 2
• MAO inhibitors (contraindicated) 1
• Verapamil (can increase risk of serotonin syndrome) 1
• Other CNS depressants including alcohol and barbiturates (enhanced effects) 1

Clinical Recommendations

When considering cyclobenzaprine use:

• Start with lower doses (5 mg) in elderly patients and those with mild hepatic impairment 1
• Titrate slowly upward if needed 1
• Avoid use in patients with moderate to severe hepatic impairment 1
• Be cautious in patients with pre-existing cardiac conduction abnormalities
• Monitor for signs of cardiac rhythm disturbances, especially when used with other medications that affect heart rhythm
• Consider alternatives in patients with cardiac disease or risk factors for arrhythmias

Monitoring Considerations

When a patient is taking cyclobenzaprine:

• Be alert for symptoms of cardiac rhythm disturbances (palpitations, dizziness, syncope)
• Monitor for signs of serotonin syndrome if combined with other serotonergic medications 1, 2
• Consider ECG monitoring in high-risk patients, especially those with pre-existing cardiac disease

Common Pitfalls

• Underestimating the cardiac effects due to its classification as a muscle relaxant rather than a psychotropic medication
• Failing to recognize cyclobenzaprine's structural similarity to TCAs and their associated cardiac risks
• Not adjusting dosage in elderly patients or those with hepatic impairment
• Missing potential drug interactions that could increase cardiac risks

While cyclobenzaprine is primarily prescribed as a muscle relaxant, healthcare providers should remain vigilant about its potential cardiac effects, especially in vulnerable populations and when used in combination with other medications that affect cardiac rhythm.