Carisoprodol and Carisoprodol Pharmacokinetics

SOMA
(carisoprodol) Tablets for Oral use

Carisoprodol DRUG DESCRIPTION

SOMA (carisoprodol) Tablets are available as 250 mg and 350 mg round, white tablets. Carisoprodol is a white, crystalline powder, having a mild, characteristic odor and a bitter taste. It is slightly soluble in water; freely soluble in alcohol, in chloroform, and in acetone; and its solubility is practically independent of pH. Carisoprodol is present as a racemic mixture. Chemically, carisoprodol is N-isopropyl-2-methyl-2-propyl-1,3-propanediol dicarbamate and the molecular formula is C₁₂H₂₄N₂O₄ , with a molecular weight of 260.33. The structural formula is:

Carisoprodol Tablets, USP are available as 350 mg round, white tablets. Carisoprodol is a white, crystalline powder, having a mild, characteristic odor and a bitter taste. It is very slightly soluble in water; freely soluble in alcohol, in chloroform, and in acetone; its solubility is practically independent of pH. Carisoprodol is present as a racemic mixture.

SOMA is indicated for the relief of discomfort associated with acute, painful musculoskeletal conditions in adults. SOMA should only be used for short periods (up to two or three weeks) because adequate evidence of effectiveness for more prolonged use has not been established and because acute, painful musculoskeletal conditions are generally of short duration.

CLINICAL PHARMACOLOGY

Carisoprodol is a centrally acting skeletal muscle relaxant that does not directly relax tense skeletal muscles in man. The mode of action of carisoprodol in relieving acute muscle spasm of local origin has not been clearly identified, but may be related to its sedative properties. In animals, carisoprodol has been shown to produce muscle relaxation by blocking interneuronal activity and depressing transmission of polysynaptic neurons in the spinal cord and in the descending reticular formation of the brain. The onset of action is rapid and lasts four to six hours.

Carisoprodol is metabolized in the liver and is excreted by the kidneys. One of the products of metabolism, meprobamate, is active as an anxiolytic. The degree to which it contributes to the efficacy of carisoprodol is unknown. Carisoprodol is dialyzable by peritoneal and hemodialysis.

Clinical Studies Experience

Because clinical studies are conducted under widely varying conditions, adverse reaction rates observed in clinical studies of a drug cannot be directly compared to rates in the clinical studies of another drug and may not reflect rates observed in practice.

The data described below are based on 1387 patients pooled from two double blind, randomized, multicenter, placebo controlled, one-week trials in adult patients with acute, mechanical, lower back pain. In these studies, patients were treated with 250 mg of SOMA, 350 mg of SOMA, or placebo three times a day and at bedtime for seven days. The mean age was about 41 years old with 54% females and 46% males and 74 % Caucasian, 16 % Black, 9% Asian, and 2% other.

There were no deaths and there were no serious adverse reactions in these two trials. In these two studies, 2.7%, 2%, and 5.4%, of patients treated with placebo, 250 mg of SOMA, and 350 mg of SOMA, respectively, discontinued due to adverse events; and 0.5%, 0.5%, and 1.8% of patients treated with placebo, 250 mg of SOMA, and 350 mg of SOMA, respectively, discontinued due to central nervous system adverse reactions.

Tell your doctor or pharmacist if you also take drugs that cause drowsiness such as: certain antihistamines (e.g., diphenhydramine), anti-anxiety drugs (e.g., diazepam), anti-seizure drugs (e.g., carbamazepine), medicine for sleep (e.g., zolpidem, temazepam), narcotic pain relievers (e.g., codeine), psychiatric medications (e.g., phenothiazines such as chlorpromazine or tricyclics such as amitriptyline), tranquilizers. Alcoholic beverages will also increase the drowsiness effect.

The usual dose of carisoprodol muscle relaxant 350 mg is unlikely to engender prominent side effects other than somnolence. The carisoprodol medication is well tolerated and without adverse effects in the majority of patients for which 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, motorcycle, 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.

The interaction of carisoprodol with opioids, essentially all opioids and other centrally-acting analgesics, but especially those of the codeine-derived subgroup of the semi-synthetic class (codeine, ethylmorphine, dihydrocodeine, morphine, meperidine, buprenorphine, hydrocodone, oxycodone, nicocodeine, benzylmorphine, the various acetylated codeine derivatives including thebacon and 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 injury and/or muscle 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.

Meprobamate and other muscle relaxing drugs often were subjects of misuse and abuse in the 1950s and 1960s. Overdose cases were reported as early as 1957 and have been reported on several occasions since then.

Carisoprodol, meprobamate, and related drugs such as tybamate have the potential to produce physical dependence with prolonged use. Withdrawal of the drug after extensive use may require hospitalization in medically-compromised patients.