Carisoprodol - Drug Monograph

Introduction

Carisoprodol is a centrally-acting skeletal muscle relaxant approved for the short-term relief of acute musculoskeletal pain and discomfort. Marketed under brand names including Soma, it is classified as a Schedule IV controlled substance in the United States due to its potential for abuse and dependence. Carisoprodol is typically prescribed as adjunctive therapy alongside rest, physical therapy, and other measures for acute musculoskeletal conditions.

Mechanism of Action

Carisoprodol's exact mechanism of action is not fully understood, but it appears to exert its effects through multiple pathways. The drug is metabolized to meprobamate, which has anxiolytic and sedative properties. Carisoprodol appears to:

• Modify central nervous system (CNS) activity
• Interfere with neuronal communication in the reticular formation and spinal cord
• Produce muscle relaxation through CNS depression rather than direct peripheral action

The drug does not directly relax skeletal muscles.

Indications

FDA-approved indications:

• Relief of acute musculoskeletal pain and discomfort
• Adjunctive therapy for acute, painful musculoskeletal conditions

Typically prescribed for short-term use (2-3 weeks) due to lack of evidence supporting longer effectiveness and increased risk of dependence with prolonged use.

Dosage and Administration

• Geriatric patients: Use with caution due to increased sensitivity
• Hepatic impairment: Contraindicated in acute intermittent porphyria; use caution in other liver diseases
• Renal impairment: Use caution (limited data available)
• Pediatric patients: Safety and effectiveness not established

Pharmacokinetics

Contraindications

• Hypersensitivity to carisoprodol or related compounds (meprobamate, mebutamate, tybamate)
• Acute intermittent porphyria
• History of allergic or idiosyncratic reactions to carbamates

Warnings and Precautions

• Potential for abuse, dependence, and withdrawal
• Sedation and impaired motor skills (caution when operating machinery)
• Seizure risk, particularly during withdrawal
• Additive effects with other CNS depressants
• Use caution in patients with history of drug abuse
• Avoid abrupt discontinuation after prolonged use
• Use with caution in patients with hepatic or renal impairment
• Potential for paradoxical reactions including agitation and insomnia

Drug Interactions

• Other CNS depressants (alcohol, benzodiazepines, opioids, sedatives): Additive CNS depression
• CYP2C19 inhibitors (omeprazole, fluvoxamine, fluoxetine): Increased carisoprodol levels
• CYP2C19 inducers (rifampin): Decreased carisoprodol efficacy
• Drugs that prolong QT interval: Possible additive effects

Adverse Effects

• Drowsiness (up to 17%)
• Dizziness (up to 7%)
• Headache (up to 5%)
• Nausea/vomiting

• Severe allergic reactions
• Seizures
• Tachycardia
• Postural hypotension
• Dependence and withdrawal syndrome
• Psychological dependence
• Motor coordination impairment

Monitoring Parameters

• Pain relief and functional improvement
• Signs of excessive sedation or CNS depression
• Evidence of abuse or dependence
• Motor coordination and cognitive function
• Withdrawal symptoms upon discontinuation
• Renal and hepatic function (periodically with long-term use)
• Concomitant medication use

Patient Education

• Take exactly as prescribed; do not exceed recommended dose
• Avoid alcohol and other CNS depressants
• Do not operate machinery or drive until effects are known
• Use for shortest duration possible (typically 2-3 weeks)
• Do not stop abruptly after prolonged use
• Store securely to prevent misuse by others
• Report any signs of allergic reaction or unusual side effects
• Be aware of potential for dependence and abuse
• Inform all healthcare providers of carisoprodol use

References

1. FDA Prescribing Information: Carisoprodol Tablets 2. Bramness JG, et al. Carisoprodol use and abuse. Pharmacoepidemiol Drug Saf. 2017;26(5):578-585 3. Reeves RR, et al. Carisoprodol: abuse potential and withdrawal syndrome. Curr Drug Abuse Rev. 2012;5(1):33-38 4. Littleton RC, et al. Skeletal muscle relaxants. In: Brunton LL, Hilal-Dandan R, Knollmann BC, eds. Goodman & Gilman's: The Pharmacological Basis of Therapeutics. 13th ed. McGraw-Hill; 2018 5. American Geriatrics Society Beers Criteria® Update Expert Panel. American Geriatrics Society 2019 Updated AGS Beers Criteria® for Potentially Inappropriate Medication Use in Older Adults. J Am Geriatr Soc. 2019;67(4):674-694 6. Chou R, et al. Systemic pharmacologic therapies for low back pain: a systematic review for an American College of Physicians clinical practice guideline. Ann Intern Med. 2017;166(7):480-492