Carisoprodol is a centrally acting muscle relaxant used to relieve acute back pain. Due to its potential for dependence and abuse, it should only be used for treatment periods of up to 2–3 weeks. Carisoprodolol is classified as a Schedule IV controlled substance, and overdose may result in central nervous system respiratory depression, seizures, or even death.
Carisoprodol is metabolized by the enzyme CYP2C19 into meprobamate, a sedative used for anxiety disorders. In individuals with low or absent CYP2C19 activity (termed “CYP2C19 poor metabolizers”), standard doses of carisoprodol can lead to a 4-fold increase in exposure to carisoprodol and a concurrent 50% decrease in meprobamate exposure compared to normal metabolizers. Approximately 3–5% of Caucasians and Africans, and 15–20% of Asians, are CYP2C19 poor metabolizers (1).
The FDA-approved drug label advises caution when prescribing carisoprodol to individuals with reduced CYP2C19 activity (Table 1) and when co-administering drugs that inhibit or induce CYP2C19 (1). The efficacy, safety, and pharmacokinetics of carisoprodol have not been established in pediatric individuals (under 16 years) or individuals over 65 years.(1). Decades of clinical use have not identified a risk of major birth defects, miscarriage, or other adverse maternal or fetal outcomes associated with carisoprodol (1).