Robaxin (Methocarbamol) Drug Information: Clinical Pharmacology

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May 27, 2012

Robaxin

Pain Management »

Introduction to pain management

Pain management can be simple or complex, depending on the cause of the pain. An example of pain that is typically less complex would be nerve root irritation from a herniated disc with pain radiating down the leg. This condition can often be alleviated with an epidural steroid injection and physical therapy. Sometimes, however, the pain does not go away. This can require a wide variety of skills and techniques to treat the pain. These skills and techniques include:

Interventional procedures
Medication management
Physical therapy or chiropractic therapy
Psychological counseling and support
Acupuncture and other alternative therapies; and
Referral to other medical specialists

All of these skills and services are necessary because pain can involve many aspects of a person's daily life.

How is pain tre...

Read the Pain Management article »

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CLINICAL PHARMACOLOGY

The mechanism of action of methocarbamol in humans has not been established, but may be due to general central nervous system (CNS) depression. It has no direct action on the contractile mechanism of striated muscle, the motor end plate or the nerve fiber.

Pharmacokinetics

In healthy volunteers, the plasma clearance of methocarbamol ranges between 0.20 and 0.80 L/h/kg, the mean plasma elimination half-life ranges between 1 and 2 hours, and the plasma protein binding ranges between 46% and 50%.

Methocarbamol is metabolized via dealkylation and hydroxylation. Conjugation of methocarbamol also is likely. Essentially all methocarbamol metabolites are eliminated in the urine. Small amounts of unchanged methocarbamol also are excreted in the urine.

Special populations

Elderly

The mean (+ SD) elimination half-life of methocarbamol in elderly healthy volunteers (mean (+ SD) age, 69 (+ 4) years) was slightly prolonged compared to a younger (mean (+ SD) age, 53.3 (+ 8.8) years), healthy population (1.5 (+ 0.4) hours versus 1.1 (+0.27) hours, respectively). The fraction of bound methocarbamol was slightly decreased in the elderly versus younger volunteers (41 to 43% versus 46 to 50%, respectively).

Renally impaired

The clearance of methocarbamol in 8 renally-impaired patients on maintenance hemodialysis was reduced about 40% compared to 17 normal subjects, although the mean (+ SD) elimination half-life in these two groups was similar: 1.2 (+ 0.6) versus 1.1 (+0.3) hours, respectively.

Hepatically impaired

In 8 patients with cirrhosis secondary to alcohol abuse, the mean total clearance of methocarbamol was reduced approximately 70% compared to that obtained in 8 age- and weight-matched normal subjects. The mean (+ SD) elimination half-life in the cirrhotic patients and the normal subjects was 3.38 (+ 1.62) hours and 1.11 (+ 0.27) hours, respectively. The percent of methocarbamol bound to plasma proteins was decreased to approximately 40 to 45% compared to 46 to 50% in the normal subjects.

Last reviewed on RxList: 11/1/2010
This monograph has been modified to include the generic and brand name in many instances.