Robaxacet (Methocarbamol – Acetaminophen)


Robaxacet is an adult medication used to treat muscle spasms and pain. It helps to relax the muscles and decrease the pain. Its effects can be felt within 1 hour.

Action And Clinical Pharmacology

This product provides a dual approach to the management of discomforts associated with musculoskeletal disorders.

The mechanism of action of methocarbamol 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. Acetaminophen is a non-opiate, non-salicylate analgesic and antipyretic.

Methocarbamol is metabolized to yield a dealkylated and a hydroxylated product. These two metabolites are found primarily as glucuronide and sulfate conjugates. The half-life of methocarbamol and its metabolites is about 2 hours. Animal studies reveal that methocarbamol crosses the placental barrier and the blood-brain barrier. Acetaminophen is conjugated in the liver to form glucuronide and sulfate conjugates. Its plasma half-life has been reported to be from 1 to 2 hours.

Indications And Clinical Uses

Pain due to or associated with skeletal muscle spasm such as acute and chronic back strains and sprains, whiplash and other traumatic injuries, myositis, pain and spasm associated with arthritis, torticollis, joint strains and sprains, bursitis, low back pain due to ill defined causes.

Children: Safety and effectiveness in children 12 years of age and younger have not been established.


Do not use this medicine:

  • if you are taking any other drugs containing methocarbamol, acetaminophen, or other ingredients in this product;
  • if you are hypersensitive to acetaminophen, methocarbamol, or other ingredients in this product.

If you are not sure whether a drug contains methocarbamol or acetaminophen, ask a doctor or pharmacist.


Do not exceed the recommended dosage as severe liver damage due to acetaminophen toxicity may occur. Avoid alcohol.

Occupational Hazards: Until the potential for producing drowsiness and dizziness has been determined, the patient should be cautioned against the operation of motor vehicles or machinery.

Tell your healthcare providers if you have liver or kidney disease.

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

Tell all healthcare providers that you are taking this drug. These are doctors, nurses, pharmacists and dentists.

Avoid driving vehicles and other activities that require increased attention until you see how this drug affects you.

Do not take the drug in higher doses than the doctor prescribed. Taking the drug in excess of the prescribed amount increases the risk of serious side effects.

It is not recommended to use other medicines containing acetaminophen. Read the instructions for medicines carefully. Taking too much acetaminophen can lead to liver problems.

Follow the instructions exactly. Do not exceed your prescribed daily dose of acetaminophen. If you are not sure what your daily dose of acetaminophen is, ask your doctor or pharmacist for it. Some patients may take this drug in doses of up to 4,000 mg per day as directed by a healthcare professional. Some patients (such as those with liver disease and children) require a lower acetaminophen dose. If you have exceeded your daily dose of acetaminophen, contact your doctor immediately, even if you do not feel worse.

Avoid drinking alcohol while taking this drug.

Talk to your doctor before using marijuana, other forms of cannabis, prescription or over-the-counter medications that can slow you down.

This drug may interfere with some lab tests. Tell all healthcare providers and lab staff that you are taking this drug.

It is used in combination with rest, physical therapy, pain medication, and other treatments.

Drug Interactions

Methocarbamol may cause a color interference in certain screening tests for 5-hydroxyindoleacetic acid (5-HIAA) and vanillylmandelic acid (VMA).

Carcinogenesis, Mutagenesis: Long-term studies in animals have not been performed to evaluate carcinogenic or mutagenic potential.

Pregnancy and breastfeeding

Pregnancy: There are no adequate and well-controlled studies of Robaxacet in pregnant women. This product should be used during pregnancy only when, in the judgment of the physician, the potential benefits outweigh the potential hazards.

Lactation: It is not known whether methocarbamol or its metabolites are secreted in human milk; there is some indication that small quantities of acetaminophen are secreted.

Tell your doctor if you are pregnant or planning to become pregnant. The benefits and risks of taking this drug during pregnancy will need to be discussed. Tell your doctor if you are breastfeeding. It is necessary to consult if the drug poses any risk to the child.

Adverse Reactions

The most common complaints to methocarbamol are drowsiness, nausea and dizziness or lightheadedness (seen in approximately 4 to 5% of patients). The following reactions have been associated with the drug, some of them rarely; in some instances, causal relationships have not been established: headache, nasal congestion, blurred vision, rash, pruritus and urticaria.

Adverse reactions that have been associated with the use of acetaminophen include: nausea, vomiting or diarrhea. Rarely, hypersensitivity reactions have been reported, as manifested by thrombocytopenic purpura, hemolytic anemia and agranulocytosis.

Gastrointestinal discomfort may be minimized by taking the dose with food.

Symptoms And Treatment Of Overdose

Symptoms: Methocarbamol: No deaths or major toxicity have been reported from overdosage with methocarbamol, administered parenterally or orally. One adult survived the deliberate ingestion of 22 to 30 g of methocarbamol without serious toxicity. Another survived 30 to 50 g. The principal symptom was drowsiness in both cases. However, 3 deaths have been reported when methocarbamol was combined with alcohol and other drugs.

Acetaminophen: Acetaminophen in massive overdosage may cause hepatic toxicity in some patients.

In adults, hepatic toxicity has rarely been reported with acute overdoses of less than 5 g. Importantly, young children seem to be more resistant than adults to the hepatotoxic effect of an acetaminophen overdose. Despite this, the measures outlined below should be initiated in any adult or child suspected of having ingested an acetaminophen overdose.

Early symptoms following a potentially hepatotoxic overdose may include: nausea, vomiting, diaphoresis and general malaise. Clinical and laboratory evidence of hepatic toxicity may not be apparent until 48 to 72 hours postingestion.

Treatment: Methocarbamol: Supportive measures include maintenance of an adequate airway, monitoring urinary output and vital signs and the administration of i.v. fluids, if necessary. There is no experience with forced diuresis or with dialysis in the treatment of methocarbamol overdose. Likewise, the usefulness of hemodialysis in managing methocarbamol overdose is unknown.

Acetaminophen: The stomach should be emptied promptly by lavage or by induction of emesis with syrup of ipecac. Patients’ estimates of the quantity of a drug ingested are notoriously unreliable. Therefore, if an acetaminophen overdose is suspected, a serum acetaminophen assay should be obtained as early as possible, but no sooner than 4 hours following ingestion. Liver function studies should be obtained initially and repeated at 24-hour intervals.

The antidote, N-acetylcysteine, should be administered as early as possible, and within 16 hours of the overdose ingestion for optimal results. Following recovery, there are no residual, structural or functional hepatic abnormalities.

Dosage And Administration

This medication is typically used 4 times a day. It may be taken with or without food. However, your health care provider may have suggested a different schedule. Generally, the medicine is used only as needed.

  • Robaxacet Tablets/Caplets: Adults and Children over 12 years: 2 caplets/tablets 4 times daily. Three caplets/tablets 4 times daily may be used in severe conditions for 1 to 3 days. These dosage recommendations provide 3.2 and 4.8 g, respectively, methocarbamol and 2.6 and 3.9 g, respectively, acetaminophen/day;
  • Robaxacet Extra Strength: Adults and Children over 12 years: 2 caplets 4 times daily. This recommended dosage provides 3.2 g methocarbamol and 4 g acetaminophen/day.

Stop using this medicine if your symptoms worsen or pain lasts for more than 5 days, or if you get any unusual symptoms like a rash or itchy skin.


Store at room temperature (15º-30ºC) away from heat, light and moisture. Do not store in the bathroom. Keep away from children and pets.


IMPORTANT: This is a summary and does NOT have all possible information about this medicine. This information does not assure that this medicine is safe or appropriate for you. This information cannot be used as a substitute for medical advice. Consult your health care provider if you have any health condition. Always ask your health care provider for complete information about this medicine and your individual health needs.

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