What is the most commonly used muscle relaxant that starts with the letter C, including its typical dosing and safety considerations?

Muscle Relaxants Starting with "C"

The most commonly used muscle relaxants starting with "C" are cisatracurium (for anesthesia/intubation) and cyclobenzaprine (for outpatient musculoskeletal pain), with distinct clinical contexts and safety profiles that determine appropriate use.

Anesthetic Muscle Relaxants: Cisatracurium

Clinical Use

• Cisatracurium is a non-depolarizing neuromuscular blocking agent used during general anesthesia to facilitate tracheal intubation and surgical procedures 1
• It is one of the currently available muscle relaxants in France and Europe, alongside atracurium, rocuronium, mivacurium, and suxamethonium 1

Dosing Considerations

• Standard dosing is typically at or above the 95% effective dose (ED95) at the adductor pollicis muscle 1
• In patients with myasthenia gravis, a 50-75% dose reduction is required due to increased sensitivity and prolonged duration of action 1
• Neuromuscular blockade monitoring is essential to avoid overdosing, particularly in patients with neuromuscular disease 1

Safety Profile

• Cisatracurium demonstrates favorable pharmacodynamics in myasthenic patients compared to other non-depolarizing agents 1
• The drug requires careful monitoring of the train-of-four (TOF) ratio, especially when baseline TOF is <0.9, which predicts greater sensitivity 1

Oral Muscle Relaxant: Cyclobenzaprine

Clinical Use and Efficacy

• Cyclobenzaprine is a tricyclic skeletal muscle relaxant used for short-term management of acute musculoskeletal spasm, particularly neck and back pain 2, 3
• It acts centrally to reduce tonic somatic motor function, likely through modulation of noradrenergic and serotonergic systems 2

Dosing Recommendations

• The optimal dose is 5 mg three times daily, which provides equivalent efficacy to 10 mg three times daily with significantly less sedation 3
• The 2.5 mg three times daily dose is not significantly more effective than placebo 3
• Onset of relief occurs within 3-4 doses of the 5 mg regimen 3
• Duration of action is 4-6 hours, necessitating three-times-daily dosing to avoid painful untreated intervals 3

Critical Safety Considerations

• Cyclobenzaprine exhibits high-affinity noncompetitive antagonism at histamine H1 receptors, explaining the significant sedation experienced by >30% of patients 4
• The drug should be held on the day of surgical procedures due to CNS depressant effects and potential interactions with anesthetic agents causing drowsiness, bradycardia, and hypotension 5
• Avoid combining with other CNS depressants (benzodiazepines, opioids, sedatives) as this significantly increases respiratory depression risk 5

Special Populations

• In elderly patients, start at lower doses and monitor closely for excessive sedation, confusion, and cardiovascular effects 5
• In hepatic or renal impairment, elimination is significantly impaired and requires dose reduction 5
• Avoid in patients with seizure disorders due to potential CNS impairment and anticholinergic effects 6

Adverse Effects

• Most common: somnolence and dry mouth, which are mild and dose-related 3
• Anticholinergic effects are expected given its tricyclic structure 2, 7
• Cyclobenzaprine has reasonable safety in overdose compared to traditional tricyclic antidepressants, but toxicity can occur in combination with other substances 7

Comparative Context

Versus Other Oral Muscle Relaxants

• Cyclobenzaprine, metaxalone, and carisoprodol have equal efficacy, but cyclobenzaprine causes more anticholinergic side effects than metaxalone 7
• Carisoprodol raises the greatest concern for physical and psychological dependence and has the greatest toxicity profile 7
• Choice of skeletal muscle relaxant should be based on adverse-effect profile, tolerability, and cost rather than efficacy differences 8

Clinical Pitfalls to Avoid

• Never confuse anesthetic neuromuscular blocking agents (cisatracurium, rocuronium) with oral skeletal muscle relaxants (cyclobenzaprine)—these are entirely different drug classes for different clinical contexts 6
• Do not prescribe cyclobenzaprine long-term; evidence supports only short-term use for acute conditions 2, 3
• Avoid combination with anticholinergic medications, particularly in older adults who have increased fall risk 6