Description

Carisoprodol, sold under the brand name Soma among others, is a medication used for musculoskeletal pain. Use is only approved for up to three weeks. Effects generally begin within half an hour and last for up to six hours. It is taken by mouth.

Common side effects include headache, dizziness, and sleepiness. A serious side effect may include addiction, allergic reactions, and seizures. In people with a sulfa allergy certain formulation may result in problems. Safety during pregnancy and breastfeeding is not clear. How it works is not clear. Some of its effects are believed to occur following being converted into meprobamate.

Carisoprodol was approved for medical use in the United States in 1959. Its approval in Europe was withdrawn in 2008. It is available as a generic medication. In the United States the wholesale cost is less than US$0.10 per dose. In 2016 it was the 181st most prescribed medication in the United States with more than 3 million prescriptions. In the United States, it is a Schedule IV controlled substance

Medical uses

Carisoprodol is meant to be used along with rest, physical therapy and other measures to relax muscles after strains, sprains and muscle injuries. It comes in tablet format and is taken by the mouth three times a day and before bed.

Side effects

The usual dose of 350 mg is unlikely to engender prominent side effects other than somnolence, and mild to significant euphoria or dysphoria, but the euphoria is generally short-lived due to the fast metabolism of carisoprodol into meprobamate and other metabolites; the euphoria derived is, according to new research, most likely due to carisoprodol’s inherent, potent anxiolytic effects that are far stronger than those produced by its primary metabolite, meprobamate, which is often misblamed for the drug-seeking associated with carisoprodol, as carisoprodol itself is responsible for the significantly more intense CNS effects than meprobamate alone. Carisoprodol has a unique mechanism of action, qualitatively different from that of meprobamate (Miltown). The medication is well tolerated and without adverse effects in the majority of patients for whom it is indicated. In some patients, however, and/or early in therapy, carisoprodol can have the full spectrum of sedative side effects and can impair the patient’s ability to operate a firearm, motor vehicles, and other machinery of various types, especially when taken with medications containing alcohol, in which case an alternative medication would be considered. The intensity of the side effects of carisoprodol tends to lessen as therapy continues, as is the case with many other drugs. Other side effects include dizziness, clumsiness, headache, fast heart rate, upset stomach, vomiting and skin rash.

The interaction of carisoprodol with essentially all opioids, and other centrally acting analgesics, but especially codeine, those of the codeine-derived subgroup of the semisynthetic class (ethylmorphine, dihydrocodeine, hydrocodone, oxycodone, nicocodeine, benzylmorphine, the various acetylated codeine derivatives including acetyldihydrocodeine, dihydroisocodeine, nicodicodeine, and others) which allows the use of a smaller dose of the opioid to have a given effect, is useful in general and especially where skeletal muscle injury and/or spasm is a large part of the problem. The potentiation effect is also useful in other pain situations and is also especially useful with opioids of the open-chain class, such as methadone, levomethadone, ketobemidone, phenadoxone, and others. In recreational drug users, deaths have resulted from carelessly combining overdoses of hydrocodone and carisoprodol. Another danger of misuse of carisoprodol and opiates is the potential to aspirate while unconscious.

Carisoprodol is metabolized by the liver and excreted by the kidneys so this drug must be used with caution with patients that have impaired hepatic or renal function. Because of the potential for more severe side effects, this drug is on the list to avoid for elderly people.

Pharmacology

Carisoprodol is a GABAergic drug

Pharmacokinetics

Carisoprodol has a rapid, 30-minute onset of action, with the aforementioned effects lasting about two to six hours. It is metabolized in the liver via the cytochrome P450 oxidase isozyme CYP2C19, excreted by the kidneys and has about an eight-hour half-life. A considerable proportion of carisoprodol is metabolized to meprobamate, which is a known drug of abuse and dependence; this could account for the abuse potential of carisoprodol (meprobamate levels reach higher peak plasma levels than carisoprodol itself following administration). Meprobamate is believed to play a significant role in the effects of carisoprodol and meprobamates long half-life results in bioaccumulation following extended periods of carisoprodol administration.

It is slightly soluble in water and freely soluble in ethanol, chloroform and acetone. The drug’s solubility is practically independent of pH.