Methocarbamol Tablets, USP Rx only

Methocarbamol tablets, USP, a carbamate derivative of guaifenesin, is a central nervous system (CNS) depressant with sedative and musculoskeletal relaxant properties.

The chemical name of methocarbamol is 3-(2-methoxyphenoxy)-1,2-propanediol 1-carbamate and has the empirical formula C ₁₁H ₁₅NO ₅. Its molecular weight is 241.24. The structural formula is shown below.

Chemical Structure

Methocarbamol is a white bulky powder, sparingly soluble in water and chloroform, soluble in alcohol only with heating and insoluble in benzene and n-hexane.

Methocarbamol tablets USP, 500 mg are available as white in color, round, beveled edge, biconvex film-coated tablet containing 500 mg of methocarbamol USP for oral administration.

Methocarbamol tablets USP, 750 mg are available as white in color, biconvex capsule shaped film-coated tablet containing 750 mg of methocarbamol USP for oral administration.

Methocarbamol tablets USP, 500 mg and 750 mg contain the following inactive ingredients: corn starch, hypromellose, magnesium stearate, polyethylene glycol, povidone, sodium lauryl sulfate, sodium starch glycolate, talc and titanium dioxide.

FDA approved dissolution test specifications differ from USP for 500 mg.

The mechanism of action of methocarbamol in humans has not been established, but may be due to general 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.

Methocarbamol tablets are indicated as an adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions. The mode of action of methocarbamol has not been clearly identified, but may be related to its sedative properties. Methocarbamol does not directly relax tense skeletal muscles in man.

Methocarbamol tablets are contraindicated in patients hypersensitive to methocarbamol or to any of the tablet components.

Since methocarbamol may possess a general CNS depressant effect, patients receiving methocarbamol should be cautioned about combined effects with alcohol and other CNS depressants.

Safe use of methocarbamol has not been established with regard to possible adverse effects upon fetal development. There have been reports of fetal and congenital abnormalities following in utero exposure to methocarbamol. Therefore, methocarbamol should not be used in women who are or may become pregnant and particularly during early pregnancy unless in the judgment of the physician the potential benefits outweigh the possible hazards (see PRECAUTIONS, Pregnancy).

Use in Activities Requiring Mental Alertness

Methocarbamol may impair mental and/or physical abilities required for performance of hazardous tasks, such as operating machinery or driving a motor vehicle. Patients should be cautioned about operating machinery, including automobiles, until they are reasonably certain that methocarbamol therapy does not adversely affect their ability to engage in such activities.

Adverse reactions reported coincident with the administration of methocarbamol include:

Body as a whole:Anaphylactic reaction, angioneurotic edema, fever, headache

Cardiovascular system:Bradycardia, flushing, hypotension, syncope, thrombophlebitis

Digestive system:Dyspepsia, jaundice (including cholestatic jaundice), nausea and vomiting

Hemic and lymphatic system:Leukopenia

Immune system:Hypersensitivity reactions

Nervous system: Amnesia, confusion, diplopia, dizziness or lightheadedness, drowsiness, insomnia, mild muscular incoordination, nystagmus, sedation, seizures (including grand mal), vertigo

Skin and special senses:Blurred vision, conjunctivitis, nasal congestion, metallic taste, pruritus, rash, urticaria

Limited information is available on the acute toxicity of methocarbamol. Overdose of methocarbamol is frequently in conjunction with alcohol or other CNS depressants and includes the following symptoms: nausea, drowsiness, blurred vision, hypotension, seizures, and coma.

In post-marketing experience, deaths have been reported with an overdose of methocarbamol alone or in the presence of other CNS depressants, alcohol or psychotropic drugs.

Treatment

Management of overdose includes symptomatic and supportive treatment. Supportive measures include maintenance of an adequate airway, monitoring urinary output and vital signs, and administration of intravenous fluids if necessary. The usefulness of hemodialysis in managing overdose is unknown.

Methocarbamol tablets, 500 mg - Adults:

Initial dosage: 3 tablets 4 times daily.

Maintenance dosage: 2 tablets 4 times daily.

Methocarbamol tablets: 750 mg - Adults:

Initial dosage: 2 tablets 4 times daily.

Maintenance dosage: 1 tablet q.4h. or 2 tablets 3 times daily.

Six grams a day are recommended for the first 48 to 72 hours of treatment. (For severe conditions 8 grams a day may be administered.) Thereafter, the dosage can usually be reduced to approximately 4 grams a day.

Methocarbamol Tablets USP, 750 mgare white in color, biconvex capsule shaped film-coated tablet, debossed with “METT” on one side and “750” on the other side. They are supplied as follows:

Bottles of 30 NDC 85509-1341-3

Bottles of 60 NDC 85509-1341-6

Store at20° to 25°C (68° to 77°F) [see USP Controlled Room Temperature].

Dispense in tight container.

For more information, call Aurobindo Pharma USA, Inc.at 1-866-850-2876.

Distributed by:
Aurobindo Pharma USA, Inc.
279 Princeton-Hightstown Road
East Windsor, NJ 08520

Manufactured by:
Aurobindo Pharma Limited
Hyderabad-500 032, India

Revised: 08/2022

Repackaged/Relabeled by:
PHOENIX RX LLC
Hatboro, PA 19040

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