What are the contraindications of Flexeril (cyclobenzaprine)?

Contraindications of Flexeril (Cyclobenzaprine)

Cyclobenzaprine (Flexeril) is absolutely contraindicated in patients with hypersensitivity to the drug, concomitant use of MAO inhibitors or within 14 days of their discontinuation, acute recovery phase of myocardial infarction, arrhythmias, heart block or conduction disturbances, congestive heart failure, and hyperthyroidism. 1

Absolute Contraindications

1. Hypersensitivity reactions:

   • To cyclobenzaprine or any component of the formulation

2. Cardiovascular conditions:

   • Acute recovery phase of myocardial infarction
   • Arrhythmias
   • Heart block or conduction disturbances
   • Congestive heart failure

3. Endocrine disorders:

   • Hyperthyroidism

4. Drug interactions:

   • Concomitant use of MAO inhibitors or within 14 days after their discontinuation (risk of hyperpyretic crisis, seizures, and death)

Relative Contraindications and Precautions

1. Serotonergic medications:

   • Use with extreme caution with SSRIs, SNRIs, TCAs, tramadol, bupropion, meperidine, or verapamil due to risk of serotonin syndrome 1, 2
   • Symptoms of serotonin syndrome include mental status changes, autonomic instability, neuromuscular abnormalities, and gastrointestinal symptoms

2. CNS depressants:

   • Caution with alcohol, barbiturates, and other CNS depressants due to enhanced effects 1

3. Pregnancy and lactation:

   • Not recommended for use in individuals who are pregnant, actively trying to conceive, or nursing 3

4. Liver and kidney disease:

   • Use with caution due to potential impaired elimination 4

5. Myasthenia gravis:

   • Contraindicated as it may interfere with pyridostigmine bromide 4

Monitoring and Precautions

1. Sedation and drowsiness:

   • More than 30% of patients experience drowsiness and sedative-hypnotic effects 5
   • Consider using lower doses (5 mg TID instead of 10 mg TID) to reduce sedation while maintaining efficacy 6

2. Serotonin syndrome risk:

   • Monitor for signs of serotonin syndrome when used with other serotonergic medications
   • Discontinue immediately if symptoms occur and provide supportive care 1, 7

3. Anticholinergic effects:

   • Monitor for dry mouth, constipation, urinary retention, and blurred vision

4. Neuropsychiatric effects:

   • Cases of delirium and hyperkinetic movement disorders have been reported 7

Dosing Considerations

• Standard dosing: 5-10 mg three times daily
• Consider starting with 5 mg three times daily to minimize sedation 4
• Limit treatment duration to short-term relief (≤21 days) when possible 4
• For elderly patients or those with liver impairment, lower doses are recommended

Mechanism Behind Contraindications

Cyclobenzaprine is structurally similar to tricyclic antidepressants and can cause similar adverse effects:

• Cardiovascular effects: Can produce arrhythmias, sinus tachycardia, and prolongation of conduction time 1
• Histamine H1 receptor antagonism: Contributes to sedation through noncompetitive antagonism of histamine H1 receptors 5
• Serotonergic effects: Can contribute to serotonin syndrome when combined with other serotonergic medications 2

By understanding these contraindications and using appropriate caution, healthcare providers can maximize the benefits of cyclobenzaprine while minimizing potential risks to patients requiring muscle relaxation therapy.