Is Flexeril (cyclobenzaprine) 10mg indicated or contraindicated in a patient with atrial fibrillation when used with gabapentin?

Flexeril (Cyclobenzaprine) is Contraindicated in Patients with Atrial Fibrillation

Cyclobenzaprine is absolutely contraindicated in patients with arrhythmias, including atrial fibrillation, regardless of concomitant gabapentin use. 1

FDA-Mandated Contraindication

The FDA drug label for cyclobenzaprine explicitly lists "patients with arrhythmias, heart block or conduction disturbances, or congestive heart failure" as contraindications to its use. 1 This contraindication also extends to patients in the acute recovery phase of myocardial infarction. 1

• The structural similarity of cyclobenzaprine to tricyclic antidepressants underlies this contraindication, as these agents can worsen cardiac conduction abnormalities and precipitate arrhythmias. 1

Gabapentin Considerations in Atrial Fibrillation

While the question asks about the combination with gabapentin, the contraindication for cyclobenzaprine exists independently:

• Gabapentin itself has been associated with increased risk of atrial fibrillation, particularly in older patients with cardiovascular comorbidities. 2, 3
• Case reports document new-onset atrial fibrillation occurring within days of gabapentin initiation, even in younger patients without traditional risk factors. 2
• Systematic review data show gabapentinoids are associated with increased cardiovascular events including atrial fibrillation with chronic use. 3

Clinical Management Algorithm

For this 67-year-old patient with atrial fibrillation and lung cancer:

1. Discontinue cyclobenzaprine immediately due to absolute contraindication. 1

2. Consider alternative muscle relaxants that do not carry cardiac contraindications (e.g., tizanidine, baclofen, or non-pharmacologic approaches).

3. Evaluate the necessity of gabapentin given its association with atrial fibrillation, particularly if the patient has other cardiovascular risk factors. 2, 3

4. Ensure appropriate atrial fibrillation management with rate control using beta-blockers or nondihydropyridine calcium channel antagonists as first-line agents. 4

5. Assess anticoagulation needs based on CHA₂DS₂-VASc score, as this 67-year-old patient likely requires anticoagulation. 4

Critical Safety Point

The combination of cyclobenzaprine with atrial fibrillation represents a clear-cut contraindication that supersedes any consideration of drug-drug interactions with gabapentin. 1 The tricyclic-like structure of cyclobenzaprine poses direct cardiac risks including worsening arrhythmias and conduction disturbances that are unacceptable in patients with pre-existing atrial fibrillation. 1