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Methocarbamol has the following structural formula:
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3-(2-methoxyphenoxy)-1,2-propanediol
1-carbamate, or methocarbamol
Robaxin Injectable is a parenteral dosage form.
Each mL contains:
Methocarbamol, USP 100 mg; Polyethylene Glycol 300, NF 0.5 mL; Water for Injection, USP q.s. pH adjusted, when necessary, with hydrochloric acid and/or sodium hydroxide.
AFTER MIXING WITH I.V. INFUSION FLUIDS, DO NOT REFRIGERATE.
The mechanism of action of methocarbamol in humans has not been established, but may be due to general central nervous system depression. It has no direct action on the contractile mechanism of striated muscle, the motor end plate or the nerve fiber.
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.
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 any of the ingredients.
Since methocarbamol may possess a general central nervous system depressant effect, patients receiving Robaxin Injectable (methocarbamol injection) 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. 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.
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 safely 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 suspected or known epileptic patients.
Safety and effectiveness in children below the age of 12 years have not been established except in tetanus. See special directions for use in tetanus.
It is not known whether this drug is secreted in human milk. As a general rule, nursing should not be undertaken while a patient is on a drug since many drugs are excreted in human milk.
Methocarbamol may cause a color interference in certain screening tests for 5-hydroxyindoleacetic acid (5-HIAA) and vanillylmandelic acid (VMA).
Dizziness, lightheadedness, drowsiness, vertigo, fainting, syncope, hypotension, gastrointestinal upset, metallic taste, thrombophlebitis, sloughing at the site of injection, pain at the site of injection, anaphylactic reaction, urticaria, pruritus, rash, conjunctivitis with nasal congestion, flushing, nystagmus, diplopia, mild muscular incoordination, bradycardia, blurred vision, headache, fever. In most cases of syncope there was spontaneous recovery. In others, epinephrine, injectable steroids and/or injectable antihistamines were employed to hasten recovery. Certain of these complaints may have been due to any overly rapid rate of intravenous injection.
The onset of convulsive seizures during intravenous administration has been reported, including instances in known epileptics. 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.
For Intravenous and Intramuscular Use Only. Total adult dosage should not exceed 30 mL (3 vials) a day for more than 3 consecutive days except in the treatment of tetanus. A like course may be repeated after a lapse of 48 hours if the condition persists. 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, 10 mL (one 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, 20 to 30 mL (two to three vials) may be required.
Directions for Intravenous Use. Robaxin Injectable may be administered undiluted directly into the vein at a maximum rate of three mL per minute. It may also be added to an intravenous drip of Sodium Chloride Injection (Sterile Isotonic Sodium Chloride Solution for Parenteral Use) or five per cent Dextrose Injection (Sterile 5 percent Dextrose Solution); one vial given as a single dose should not be diluted to more than 250 mL for I. V. infusion. Care should be exercised to avoid vascular extravasation of this hypertonic solution which may result in thrombophlebitis. It is preferable that the patient be in a recumbent position during and for at least 10 to 15 minutes following the injection.
Directions for Intramuscular Use. When the intramuscular route is indicated, not more than five mL (one-half vial) should be injected into each gluteal region. The injections may be repeated at eight hour intervals, if necessary. When satisfactory relief of symptoms is achieved, it can usually be maintained with tablets.
Special Directions for Use in Tetanus: There is clinical evidence which suggests that methocarbamol may have a beneficial effect in the control of the neuromuscular manifestations of tetanus. It does not, however, replace the usual procedure of debridement, tetanus antitoxin, penicillin, tracheotomy, attention to fluid balance, and supportive care. Robaxin Injectable should be added to the regimen as soon as possible.
For adults: Inject one or two vials directly into the tubing of a previously inserted indwelling needle. An additional 10 mL or 20 mL may be added to the infusion bottle so that a total of up to 30 mL (three vials) is given as the initial dose (note Precautions). This procedure should be repeated every six hours until conditions allow for the insertion of a nasogastric tube. Crushed Robaxin (methocarbamol) tablets suspended in water or saline may then be given through this tube. Total daily oral doses up to 24 grams may be required as judged by patient response.
For children: A minimum initial dose of 15 mg/kg is recommended. This dosage may be repeated every six hours as indicated. The maintenance dosage may be given by injection into the tubing or by I.V. infusion with an appropriate quantity of fluid. See directions for I.V. use.
Robaxin Injectable--10 mL single dose vials in packages of 5 (NDC 0031-7409-87) and 25 (NDC 0031-7409-94).
Manufactured for Pharmaceutical Division, A. H. ROBINS CO., Richmond, VA 23220, by ELKINS-SINN, INC., Cherry Hill, NJ 08034, a subsidiary of A.H. Robins.
J-9667 rev. 12/81
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