Chlorzoxazone

Chlorzoxazone is a prescription medication used for treating musculoskeletal pain.

• Chlorzoxazone is available under the following different brand names: Parafon Forte DSC, Lorzone

Adult and pediatric dosage

Tablet

• 375mg
• 500mg
• 750mg

Musculoskeletal Pain

Adult dosage

• 250-750 mg orally every 6-8 hours

Pediatric dosage

• 20 mg/kg/day orally divided every 6-8 hours or 600 mg/m²/day orally divided every 6-8 hours.

Geriatric dosage

• 250 mg orally every 6-12 hours; increase if needed to 750 mg orally every 6-8 hours

Dosage Considerations – Should be Given as Follows: 

• See “Dosages”

Common side effects of Chlorzoxazone include:

• gastrointestinal bleeding
• drowsiness
• dizziness
• lightheadedness
• feeling unwell
• over-stimulation, and
• rarely, allergic-type skin rashes.

Serious side effects of Chlorzoxazone include:

• a light-headed feeling,
• skin rash, itching, or redness,
• liver problems--stomach pain (upper right side), loss of appetite, vomiting, fever, unusual tiredness, dark urine, or jaundice (yellowing of the skin or eyes), or
• signs of stomach bleeding--bloody or tarry stools, coughing up blood, or vomit that looks like coffee grounds.

Rare side effects of Chlorzoxazone include:

• none 

This is not a complete list of side effects and other serious side effects or health problems that may occur as a result of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

• Chlorzoxazone has severe interactions with no other drugs.
• Chlorzoxazone has serious interactions with the following drugs:
  • benzhydrocodone/acetaminophen
  • calcium/magnesium/potassium/sodium oxybates
  • hydrocodone
  • lonafarnib
  • metoclopramide intranasal
  • sodium oxybate
  • sufentanil SL
• Chlorzoxazone has moderate interactions with at least 161 drugs.
• Chlorzoxazone has minor interactions with the following drugs:
  • eucalyptus
  • ruxolitinib
  • ruxolitinib topical
  • sage

This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns.

Contraindications

• Hypersensitivity to anticholinergic drugs
• Narrow-angle glaucoma, synechia (adhesions) between iris and eye lens, myasthenia gravis, obstructive uropathy, paralytic ileus, severe ulcerative colitis, toxic megacolon, acute hemorrhage with cardiovascular instability, thyrotoxicosis

Effects of drug abuse

• None

Short-Term Effects

• See “What Are Side Effects Associated with Using Chlorzoxazone?”

Long-Term Effects

• See “What Are Side Effects Associated with Using Chlorzoxazone?”

Cautions

• May cause CNS depression and impair physical and mental alertness; avoid performing tasks that require mental alertness
• May take with food to avoid stomach upset
• Poor tolerance by the elderly
• Hepatotoxicity
• Serious (including fatal) hepatocellular toxicity has been reported rarely in patients receiving therapy; the mechanism is unknown but appears to be idiosyncratic and unpredictable
• Factors predisposing patients to this rare event are not known
• Patients should be instructed to report early signs and/or symptoms of hepatotoxicity such as fever, rash, anorexia, nausea, vomiting, fatigue, right upper quadrant pain, dark urine, or jaundice; therapy should be discontinued immediately, and a physician consulted if signs or symptoms develop
• Therapy should also be discontinued if a patient develops abnormal liver enzymes (e.g., AST, ALT, alkaline phosphatase, and bilirubin)
• The concomitant use of alcohol or other central nervous system depressants may have an additive effect

Pregnancy and Lactation

• Use with caution if the benefits outweigh the risks during pregnancy.
• Lactation
  • Not known if excreted in breast milk