March 2019

Carisoprodol

Dr. Joseph E. Graas, Scientific Director
Dr. Edward Moore, Medical Director
Dr. Paul Robandt, Scientific Director

Carisoprodol is a centrally-acting muscle relaxant first researched at Wallace Laboratories and marketed in the US in 1959.  The drug was a modification of meprobamate (Miltown, Equanil) and was supposed to have better muscle-relaxing properties with less potential for abuse and overdose.   Carisoprodol is marketed as Soma by Mylan Specialty L.P.  Supplied as 250 milligram and 350 milligram tablets, carisoprodol was put on schedule IV by the United States Drug Enforcement Administration (DEA) in 2011.  Prior to that it was unscheduled.  Carisoprodol is also formulated with codeine and aspirin for short-term use for acute, painful musculoskeletal conditions in adults.  It is believed to have synergistic pain-relief and muscle relaxant properties in this formulation.

Carisoprodol is metabolized to meprobamate, which has significant barbiturate-like action.  However, carisoprodol has a different mechanism of action, particularly in its anxiolytic effects.  Early in treatment, the side effects of drowsiness, dizziness, vertigo, ataxia and tremors can be pronounced but tend to subside with increasing duration of use.   Researchers have found that long-term users of carisoprodol also used concurrent opioids more frequently and, more commonly, had past diagnoses of other drug abuse.   They were also more likely to pay for carisoprodol out of pocket after insurance coverage for the drug had stopped.1

Users have found that the combination of a benzodiazepine, opioid and carisoprodol intensify and potentiate the “high” as opposed to taking any of the same drugs individually.  The combination has been nicknamed the “holy trinity” and is actively sought out by drug users.2  The risk of combining benzodiazepines with opioids is well known, and concurrent use of benzodiazepines with opioids is contraindicated in chronic non-cancer pain.   However, carisoprodol and other skeletal muscle relaxants are not included in any prescription advisory.  Carisoprodol alone or with other agents (opioids and benzodiazepines, in particular) reportedly caused more than 30,000 emergency department visits in 2009.  The number of carisoprodol related visits tripled from 2004 to 2009, and most of the incidents also involved other drugs.  Of these cases, 35-42 percent resulted in hospitalization.3

Title 21 of the Code of Federal Regulations states, “A prescription for a controlled substance to be effective must be issued for a legitimate medical purpose by an individual practitioner acting in the usual course of his professional practice.  The responsibility for the proper prescribing and dispensing of controlled substances is upon the prescribing practitioner, but a corresponding responsibility rests with the pharmacist who fills the prescription.”  Physicians and pharmacists are gradually becoming aware of the potential of abuse for carisoprodol and are examining polydrug use more closely.

REFERENCES

  1. Owens, C., et. al., Abuse Potential of Carisoprodol: A Retrospective Review of Idaho Medicaid Pharmacy and Medical Claims Data, Clin.  Therapeutics, October 2007, Volume 29, Issue 10, Pages 2222–2225
  2. Forrester MB. Ingestions of hydrocodone, carisoprodol, and alprazolam in combination reported to Texas poison centers.  J Addict Dis 2011; 30:110–5.
  3. Substance Abuse and Mental Health Administration, Drug Abuse Warning Network Report, 27 October 2011