Methocarbamol (injection)

Methocarbamol (injection)
Adult Indications & Dosage
Pediatric Indications & Dosage
Contraindications
Warnings & Precautions
Adverse Reactions
Drug Interactions
Use in Specific Populations
Administration & Monitoring
Overdosage
Pharmacology
Clinical Studies
How Supplied
Images
Patient Counseling Information
Precautions with Alcohol
Brand Names
Look-Alike Names

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Shanshan Cen, M.D. [2]

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Overview

Methocarbamol (injection) is a central nervous system (CNS) depressant with sedative and musculoskeletal relaxant properties that is FDA approved for the treatment of rest, physical therapy, and can be used as an adjunct to other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions. Common adverse reactions include dizziness, headache, lightheadedness, somnolence.

Adult Indications and Dosage

FDA-Labeled Indications and Dosage (Adult)

Indications

The injectable form of methocarbamol is 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 this drug has not been clearly identified, but may be related to its sedative properties. Methocarbamol does not directly relax tense skeletal muscles in man.

Dosage

Total adult dosage should not exceed 30 mL (3 vials) a day for more than 3 consecutive days except in the treatment of tetanus. If the condition persists, a like course may be repeated after a drug-free interval of 48 hours. Dosage and frequency of injection should be based on the severity of the condition being treated and therapeutic response noted.

For the relief of symptoms of moderate degree, one dose of 1 gram (one 10 mL vial) may be adequate. Ordinarily this injection need not be repeated, as the administration of the oral form will usually sustain the relief initiated by the injection. For the severest cases or in postoperative conditions in which oral administration is not feasible, additional doses of 1 gram may be repeated every 8 hours up to a maximum of 3 g/day for no more than 3 consecutive days.

Off-Label Use and Dosage (Adult)

Guideline-Supported Use

There is limited information regarding Off-Label Guideline-Supported Use of Methocarbamol (injection) in adult patients.

Non–Guideline-Supported Use

There is limited information regarding Off-Label Non–Guideline-Supported Use of Methocarbamol (injection) in adult patients.

Pediatric Indications and Dosage

FDA-Labeled Indications and Dosage (Pediatric)

Indications

• Tetanus

Dosage

A minimum initial dose of 15 mg/kg or 500 mg/m2 is recommended. This dosage may be repeated every six hours, if required. The total dose should not exceed 1.8 g/m2 for 3 consecutive days. The maintenance dosage may be given by injection into tubing or by I.V. infusion with an appropriate quantity of fluid. See directions for I.V. use.

Off-Label Use and Dosage (Pediatric)

Guideline-Supported Use

There is limited information regarding Off-Label Guideline-Supported Use of Methocarbamol (injection) in pediatric patients.

Non–Guideline-Supported Use

There is limited information regarding Off-Label Non–Guideline-Supported Use of Methocarbamol (injection) in pediatric patients.

Contraindications

ROBAXIN Injectable should not be administered to patients with known or suspected renal pathology. This caution is necessary because of the presence of polyethylene glycol 300 in the vehicle.

A much larger amount of polyethylene glycol 300 than is present in recommended doses of ROBAXIN Injectable is known to have increased pre-existing acidosis and urea retention in patients with renal impairment. Although the amount present in this preparation is well within the limits of safety, caution dictates this contraindication.

ROBAXIN Injectable is contraindicated in patients hypersensitive to methocarbamol or to any of the injection components.

Warnings

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

Safe use of ROBAXIN Injectable has not been established with regard to possible adverse effects upon fetal development. There have been very rare reports of fetal and congenital abnormalities following in utero exposure to methocarbamol. Therefore, ROBAXIN Injectable 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.

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.

Use in Patients with Hypersensitivity to Latex

The vial stopper contains dry natural rubber that may cause hypersensitivity reactions when handled by or when the product is injected in persons with known or possible latex sensitivity.

Precautions

As with other agents administered either intravenously or intramuscularly, careful supervision of dose and rate of injection should be observed. Rate of injection should not exceed 3 mL per minute–i.e., one 10 mL vial in approximately three minutes. Since ROBAXIN Injectable is hypertonic, vascular extravasation must be avoided. A recumbent position will reduce the likelihood of side reactions.

Blood aspirated into the syringe does not mix with the hypertonic solution. This phenomenon occurs with many other intravenous preparations. The blood may be injected with the methocarbamol, or the injection may be stopped when the plunger reaches the blood, whichever the physician prefers.

The total dosage should not exceed 30 mL (three vials) a day for more than three consecutive days except in the treatment of tetanus.

Caution should be observed in using the injectable form in patients with suspected or known seizure disorders.

Adverse Reactions

Clinical Trials Experience

The following adverse reactions have been reported coincident with the administration of methocarbamol. Some events may have been due to an overly rapid rate of intravenous injection.

Body as a Whole Anaphylactic reaction, angioneurotic edema, fever, headache

Cardiovascular System Bradycardia, flushing, hypotension, syncope, thrombophlebitis

In most cases of syncope there was spontaneous recovery. In others, epinephrine, injectable steroids, and/or injectable antihistamines were employed to hasten recovery.

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

The onset of convulsive seizures during intravenous administration of methocarbamol has been reported in patients with seizure disorders. The psychic trauma of the procedure may have been a contributing factor. Although several observers have reported success in terminating epileptiform seizures with ROBAXIN Injectable, its administration to patients with epilepsy is not recommended.

Skin and Special Senses Blurred vision, conjunctivitis, nasal congestion, metallic taste, pruritus, rash, urticaria

Other Pain and sloughing at the site of injection

Postmarketing Experience

There is limited information regarding Postmarketing Experience of Methocarbamol (injection) in the drug label.

Drug Interactions

Methocarbamol may inhibit the effect of pyridostigmine bromide. Therefore, methocarbamol should be used with caution in patients with myasthenia gravis receiving anticholinesterase agents.

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

Use in Specific Populations

Pregnancy

Pregnancy Category (FDA): C Animal reproduction studies have not been conducted with methocarbamol. It is also not known whether methocarbamol can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. ROBAXIN Injectable should be given to a pregnant woman only if clearly needed.

Safe use of ROBAXIN Injectable 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, ROBAXIN Injectable 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.
Pregnancy Category (AUS): B2 There is no Australian Drug Evaluation Committee (ADEC) guidance on usage of Methocarbamol (injection) in women who are pregnant.

Labor and Delivery

There is no FDA guidance on use of Methocarbamol (injection) during labor and delivery.

Nursing Mothers

Methocarbamol and/or its metabolites are excreted in the milk of dogs; however, it is not known whether methocarbamol or its metabolites are excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when ROBAXIN Injectable is administered to a nursing woman.

Pediatric Use

Safety and effectiveness of ROBAXIN Injectable in pediatric patients have not been established except in tetanus.

Geriatic Use

There is no FDA guidance on the use of Methocarbamol (injection) with respect to geriatric patients.

Gender

There is no FDA guidance on the use of Methocarbamol (injection) with respect to specific gender populations.

Race

There is no FDA guidance on the use of Methocarbamol (injection) with respect to specific racial populations.

Renal Impairment

There is no FDA guidance on the use of Methocarbamol (injection) in patients with renal impairment.

Hepatic Impairment

There is no FDA guidance on the use of Methocarbamol (injection) in patients with hepatic impairment.

Females of Reproductive Potential and Males

There is no FDA guidance on the use of Methocarbamol (injection) in women of reproductive potentials and males.

Immunocompromised Patients

There is no FDA guidance one the use of Methocarbamol (injection) in patients who are immunocompromised.

Administration and Monitoring

Administration

• Intramuscular

• Intravenous

Monitoring

There is limited information regarding Monitoring of Methocarbamol (injection) in the drug label.

IV Compatibility

There is limited information regarding IV Compatibility of Methocarbamol (injection) in the drug label.

Overdosage

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.

Pharmacology

Methocarbamol (injection)
Systematic (IUPAC) name
(RS)-2-hydroxy-3-(2-methoxyphenoxy)propyl carbamate
Identifiers
CAS number	532-03-6
ATC code	M03BA03
PubChem	4107
DrugBank	DB00423
Chemical data
Formula	Template:OrganicBox atomTemplate:OrganicBox atomTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBox atomTemplate:OrganicBoxTemplate:OrganicBox atomTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBoxTemplate:OrganicBox
Mol. mass	241.241 g/mol
SMILES	eMolecules & PubChem
Pharmacokinetic data
Bioavailability	?
Metabolism	Hepatic
Half life	1.14–1.24 hours
Excretion	?
Therapeutic considerations
Pregnancy cat.	B2(AU) C(US)
Legal status	[[Prescription drug|Template:Unicode-only]](US) OTC(Canada)
Routes	Oral, intravenous

Mechanism of Action

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.

Structure

ROBAXIN (methocarbamol injection, USP) Injectable, a carbamate derivative of guaifenesin, is a central nervous system (CNS) depressant with sedative and musculoskeletal relaxant properties. It is a sterile, pyrogen-free solution intended for intramuscular or intravenous administration.

Each mL contains: methocarbamol, USP 100 mg, polyethylene glycol 300, NF 0.5 mL, Water for Injection, USP q.s. The pH is adjusted, when necessary, with hydrochloric acid and/or sodium hydroxide. The chemical name of methocarbamol is 3‑(2‑methoxyphenoxy)‑1,2-propanediol 1‑carbamate and has the empirical formula of C11H15NO5. Its molecular weight is 241.24. The structural formula is shown below:

File:Methocarbamol injection1.png

This image is provided by the National Library of Medicine.

Methocarbamol is a white powder, sparingly soluble in water and chloroform, soluble in alcohol (only with heating) and propylene glycol, and insoluble in benzene and n‑hexane.

ROBAXIN Injectable has a pH between 3.5 and 6.0.

Pharmacodynamics

There is limited information regarding Pharmacodynamics of Methocarbamol (injection) in the drug label.

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.

Nonclinical Toxicology

Drug and/or Laboratory Test Interactions

Methocarbamol may cause a color interference in certain screening tests for 5‑hydroxyindoleacetic acid (5-HIAA) using nitrosonaphthol reagent and in screening tests for urinary vanillylmandelic acid (VMA) using the Gitlow method.

Carcinogenesis and Mutagenesis and Impairment of Fertility

Long-term studies to evaluate the carcinogenic potential of methocarbamol have not been performed. No studies have been conducted to assess the effect of methocarbamol on mutagenesis or its potential to impair fertility.

Clinical Studies

There is limited information regarding Clinical Studies of Methocarbamol (injection) in the drug label.

How Supplied

ROBAXIN Injectable (100 mg/mL) supplied in – 10 mL single dose vials in packages of 25 (NDC 60977-150-01).

Storage

Store at 20°- 25°C (68°- 77°F), excursions permitted to 15°- 30°C (59°- 86°F).

Images

Drug Images

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Package and Label Display Panel

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This image is provided by the National Library of Medicine.

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Patient Counseling Information

Patients should be cautioned that methocarbamol may cause drowsiness or dizziness, which may impair their ability to operate motor vehicles or machinery.

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

Precautions with Alcohol

• Alcohol-Methocarbamol (injection) interaction has not been established. Talk to your doctor about the effects of taking alcohol with this medication.

Brand Names

• ROBAXIN ®

Look-Alike Drug Names

• A® — B®

Drug Shortage Status

Price

References

The contents of this FDA label are provided by the National Library of Medicine.