Tradename
Myolgin
Generic Name
Chlorzoxazone, Paracetamol
Category
Musculoskeletal System
Form
Capsules
Composition
Chlorzoxazone.............250 mg
Paracetamol................300 mg
Description
Muscle rexalaxant and analgesic
Properties/Actions
Pharmacodynamics
Chlorzoxazone is a centrally acting muscle relaxant, which exerts its effect primarily at the level of the spinal cord and sub-cortical areas of the brain to inhibit the reflex arc responsible for muscle spasm.
Paracetamol has an analgeisc effect on skeletal muscle pain through the inhibition of prostaglandin synthesis in the central nervous system.

Pharmacokinetics
Chlorzoxazone is reported to be completely absorbed after oral administration and peak serum concentrations are achieved after 1 to 2 hours. Following oral administration, its effect begins within an hour.
Paracemtaol is metabolized in the liver and excreted in the urine mianly as glucuronide and sulphate conjugates. Less than 5% is excreted as unmodified paracetamol. Binding to plasma proteins is minimal at therpeutic concentrations.
Indications
Myolgin capsules offer quick relief of pain and restore mobility even in severely painful spasms of the skeletal muscles as in cases of:
  • Sprains and strains
  • Traumatic muscle spasm
  • Reflex muscle spasm associated with rheumatic diseases
  • Lumbago
  • Myalgia
  • Tension headache
  • Troticollis
  • Cervical root syndrome
Contraindications
Hypersensitivity to any of the components of the preparation.
Drug Interactions
The following interactions have been noted:
  • The anticoagulant effect of warfarin and other coumarins may be enhanced by prolonged regular daily dose of paracetamol with increased risk of bleeding; occasional doses have no significant effect.
  • Isoniazid inhibits the clearance of chlorzoxazone.
  • Chlorzoxzone has been associated with clinical exacerbation of porphyria and is considered usafe in porphyric patients.
Side Effects/Adverse Effects
Due to Chlorzoxazone:
In rare cases, some mild and transient gastrointestinal disturbances, drowsiness, dizziness, malaise or restlesness may occur. Hypersensitivity reactions and very rare cases of jaundice were reported.
N.B. Rarely, urine discoloration may occur due to the phenolic metabolite of chlorzoxazone, which is of no significance.
Due to Paracetamol:

Usually mild and rare. They include hematological reactions, skin eruptions and aggravation of bronchospasm in patients sensitive to aspirin and other NSAIDs.
Pregnancy & Lactation
Dosage & Administration
Unless otherwise prescribed by the physician, the dose is 1 to 2 capsules three times daily after meals, according to the severity of the case.
Overdosage
Following overdosage, there may be gastrointestinal disturbances, drowsiness, dizziness, headache, malaise and slugishness followed by marked loss of muscle tone, hypotension and respiratory depression.
Treatment consists of emptying the stomach by lavage or emesis, followed by administration of activated charcoal or supportive treatment.
Administration of N-acetylcysteine or methionine may be required as a paracetamol antidote.
Paracetamol overdose may cause liver failure.
Warnings
Chlorzoxazone should not be given to patients with impaired liver functions and should be discontinued if signs of liver damage occur.
The daily dose should not exceed 4 grams of paracetamol and 3 grams of cholorzoxazone.
Notes
Storage
Store below 30°C.
Packaging
Strips of 10 capsules in a pack of 1 or 2 strips.
Manufacturer
GlaxoSmithKline (GSK)
Date Added/Updated
2nd October 2009 4:52 pm
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