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Abuse of skeletal muscle relaxants

American Family Physician, Oct, 1991 by Nancy C. Elder

Substance abuse and dependence are steadily increasing problems in the United States. Many substances of abuse are prescription medications or closely related to drugs with established medical uses. Most physicians are aware of the more commonly abused prescription medications, such as benzodiazepines and narcotics. [1] The abuse potential of centrally acting skeletal muscle relaxants is not as well recognized.

Illustrative Case

A 38-year-old man came to a county health department requesting refills of atenolol for hypertension and carisoprodol for a "bad back." The patient gave a vague history of back problems dating from an accident that had occurred four years earlier. An orthopedic surgical procedure had been performed without benefit. He was unemployed because of chronic back pain.

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The patient was obese; trunk flexion at the waist was limited to 15 degrees, as was lateral bending to both sides. A surgical scar was noted in the lumbar region, and palpalation revealed moderate tenderness over the right lower lumbar and sacroiliac areas. Sensation was decreased along the lateral side of the right thigh, but all reflexes and muscle strength in the legs were normal and symmetric.

The prescriptions for carisoprodol and atenolol were renewed, and medical records were requested from the patient's previous physician. Two months after the first visit, the patient requested a refill of carisoprodol, but this request was denied. One month later, the patient was re-examined, and the clinical picture had remained unchanged. The patient requested more carisoprodol, and the prescription was renewed at this time. Later that week, a community pharmacist reported that the patient had returned for a refill of the carisoprodol prescription only four days after receiving a month's supply. The pharmacist was instructed not to refill the prescription until the next month.

Two months later, the patient requested another refill of the carisoprodol prescription. The patient's medical records had not yet arrived from his previous physician, and a second request for the records was made. A one-month supply of carisoprodol was prescribed pending receipt of the records. Later that day, another tommunity pharmacist telephoned to confirm the prescription, because the patient had received this medication from two other physicians.

Telephone calls to various community pharmacies and emergency departments revealed that in the preceding four months the patient had filled prescriptions from seven different physicians for at least 1,132 carisoprodol tablets. The patient had not requested or received narcotics during this time.

Before the patient could be seen again in the office, he died of cardiac arrhythmia due to chronic drug abuse. Carisoprodol levels were not measured, but toxicology analysis revealed small amounts of carboxy-THC, hydromorphone, diphenhydramine, nicotine, caffeine and benzodiazepines in the urine.

The patient's previous medical records revealed a history of carisoprodol abuse and complications. Three years before the patient's death, an orthopedic surgeon had noted that the patient was using "too much" carisoprodol. One year later, the patient had been hospitalized because of generalized seizures after an overdose of carisoprodol. The patient had recovered from this episode within 24 hours and left the hospital against medical advice, thus limiting further evaluation.

Discussion

Biochemically, skeletal muscle relaxants are a diverse group of drugs. Cyclobenzaprine (Flexeril), for example, is closely related to the tricyclic antidepressants. [2] Baclofen (Lioresal) is a gamma-aminobutyric acid derivative, [3] and carisoprodol (Soma) is chemically related to meprobamate (Equanil, Miltown). [4] The mechanism of action of skeletal muscle relaxants is unknown, but animal studies suggest that they preferentially depress polysynaptic reflexes. [5,6] Because of this pharmacologic diversity, the risk for misuse, the lethal dose and the treatment in case of overdosage are specific to the drug ingested.

Despite their unrelated chemical structures, all of these agents possess sedative properties, [5] and they are abused mainly for this effect. At high doses, skeletal muscle relaxants have been described as producing "a buzz" (baclofen), [3] "euphoria" (carisoprodol) [4] and "mood enhancement and pleasant disperceptions" (orphenadrine [Norgesic]). [7]

The extent to which skeletal muscle relaxants are abused is unclear, since only limited published data are available. Of cases involving skeletal muscle relaxant ingestion reported to the Rush-Presbyterian-St. Luke's Poison Control Center in Chicago over a one-year period, 10.7 percent were related to intentional misuse or abuse. [8] The Drug Abuse Warning Network collects data on abused substances identified during encounters at 756 hospital emergency departments. In 1987, skeletal muscle relaxants were reported as the substance of abuse in 1,324 instances. Cyclobenzaprine and carisoprodol were ranked 44th and 54th, respectively, among 234 abused drugs reported to the network. [9]

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Abuse of skeletal muscle relaxants

American Family Physician, Oct, 1991 by Nancy C. Elder

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