Chlorzoxazone

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Chlorzoxazone Brand Names

Lorzone | Parafon Forte DSC | Relax-DS | Remular S

What is Chlorzoxazone

Chlorzoxazone is an oral, centrally acting, skeletal muscle-relaxing agent with sedative properties.

Chlorzoxazone is used as an adjunct to rest, physical therapy, analgesics and other measures in the treatment of acute musculoskeletal pain.

Chlorzoxazone does not directly relax tense skeletal muscles in man, so the mode of action may be related to the sedative properties. Use of this drug has largely fallen out of favor due to the potential for sedative side effects, questionable efficacy, and a potential risk for liver toxicity.

Chlorzoxazone is a known metabolite of zoxazolamine, a hepatotoxic skeletal muscle relaxant.

By 1961, zoxazolamine had been associated with 15 hepatotoxic fatalities.

At one time, chlorzoxazone was available in combination with acetaminophen, another drug known to be hepatotoxic when used in excess; however, this combination is no longer marketed.

A single-dose rechallenge in a patient who experienced liver toxicity proved that chlorzoxazone was the hepatotoxic agent, not acetaminophen.

There are a general lack of placebo-controlled randomized trials to demonstrate efficacy of the drug in acute musculoskeletal pain conditions. In one trial, the drug had no benefit vs. placebo to patients receiving morphine patient controlled analgesia in the adjunctive treatment of acute back pain following spinal surgery.

Muscle relaxants such as chlorzoxazone may still be combined with other analgesics if needed for relief of pain secondary to muscle spasms, although it would be best to avoid hepatotoxic agents concurrently.

Chlorzoxazone was officially FDA-approved in 1987, but pharmaceutical products had been marketed many years prior to that date.

Indications

  • musculoskeletal pain

For adjunctive therapy to rest, physical therapy, and other measures for musculoskeletal pain associated with acute musculoskeletal conditions

Side Effects

  1. anaphylactoid reactions
  2. angioedema
  3. cholestasis
  4. diarrhea
  5. dizziness
  6. drowsiness
  7. dyspepsia
  8. ecchymosis
  9. elevated hepatic enzymes
  10. GI bleeding
  11. headache
  12. hepatic failure
  13. hepatic necrosis
  14. hepatitis
  15. hepatotoxicity
  16. hyperbilirubinemia
  17. jaundice
  18. malaise
  19. nausea
  20. petechiae
  21. rash
  22. torticollis
  23. urine discoloration
  24. urticaria
  25. vomiting

Monitoring Parameters

  • LFTs
  • serum bilirubin

Contraindications

  • breast-feeding
  • children
  • coadministration with other CNS depressants
  • driving or operating machinery
  • ethanol ingestion
  • geriatric
  • hepatic disease
  • hepatitis
  • infants
  • jaundice
  • pregnancy
  • renal failure
  • renal impairment

Interactions

  • Acetaminophen; Butalbital
  • Acetaminophen; Butalbital; Caffeine
  • Acetaminophen; Butalbital; Caffeine; Codeine
  • Acetaminophen; Caffeine; Dihydrocodeine
  • Acetaminophen; Caffeine; Magnesium Salicylate; Phenyltoloxamine
  • Acetaminophen; Caffeine; Phenyltoloxamine; Salicylamide
  • Acetaminophen; Chlorpheniramine; Dextromethorphan; Phenylephrine
  • Acetaminophen; Chlorpheniramine; Dextromethorphan; Pseudoephedrine
  • Acetaminophen; Chlorpheniramine; Phenylephrine; Phenyltoloxamine
  • Acetaminophen; Codeine
  • Acetaminophen; Dextromethorphan; Doxylamine
  • Acetaminophen; Dichloralphenazone; Isometheptene
  • Acetaminophen; Diphenhydramine
  • Acetaminophen; Hydrocodone
  • Acetaminophen; Oxycodone
  • Acetaminophen; Pentazocine
  • Acetaminophen; Tramadol
  • Acrivastine; Pseudoephedrine
  • Alfentanil
  • Alprazolam
  • Amitriptyline
  • Amitriptyline; Chlordiazepoxide
  • Amobarbital
  • Amoxapine
  • Anxiolytics; Sedatives; and Hypnotics
  • Apomorphine
  • Aspirin, ASA; Butalbital; Caffeine
  • Aspirin, ASA; Butalbital; Caffeine; Codeine
  • Aspirin, ASA; Caffeine; Dihydrocodeine
  • Aspirin, ASA; Carisoprodol; Codeine
  • Aspirin, ASA; Oxycodone
  • Atropine; Difenoxin
  • Atropine; Diphenoxylate
  • Atropine; Hyoscyamine; Phenobarbital; Scopolamine
  • Azelastine
  • Azelastine; Fluticasone
  • Bacitracin
  • Barbiturates
  • Belladonna Alkaloids; Ergotamine; Phenobarbital
  • Belladonna; Opium
  • Benzhydrocodone; Acetaminophen
  • Benzodiazepines
  • Botulinum Toxins
  • Brompheniramine
  • Brompheniramine; Carbetapentane; Phenylephrine
  • Brompheniramine; Dextromethorphan; Guaifenesin
  • Brompheniramine; Guaifenesin; Hydrocodone
  • Brompheniramine; Hydrocodone; Pseudoephedrine
  • Brompheniramine; Pseudoephedrine
  • Buprenorphine
  • Buprenorphine; Naloxone
  • Buspirone
  • Butabarbital
  • Butorphanol
  • Cannabidiol
  • Carbetapentane; Chlorpheniramine
  • Carbetapentane; Chlorpheniramine; Phenylephrine
  • Carbetapentane; Diphenhydramine; Phenylephrine
  • Carbetapentane; Guaifenesin
  • Carbetapentane; Guaifenesin; Phenylephrine
  • Carbetapentane; Phenylephrine
  • Carbetapentane; Phenylephrine; Pyrilamine
  • Carbetapentane; Pseudoephedrine
  • Carbetapentane; Pyrilamine
  • Carbidopa; Levodopa; Entacapone
  • Carbinoxamine
  • Carbinoxamine; Dextromethorphan; Pseudoephedrine
  • Carbinoxamine; Hydrocodone; Phenylephrine
  • Carbinoxamine; Hydrocodone; Pseudoephedrine
  • Carbinoxamine; Phenylephrine
  • Carbinoxamine; Pseudoephedrine
  • Cenobamate
  • Cetirizine
  • Cetirizine; Pseudoephedrine
  • Chlophedianol; Dexbrompheniramine
  • Chlophedianol; Dexchlorpheniramine; Pseudoephedrine
  • Chloral Hydrate
  • Chlorcyclizine
  • Chlordiazepoxide
  • Chlordiazepoxide; Clidinium
  • Chlorpheniramine
  • Chlorpheniramine; Codeine
  • Chlorpheniramine; Dextromethorphan
  • Chlorpheniramine; Dextromethorphan; Phenylephrine
  • Chlorpheniramine; Dihydrocodeine; Phenylephrine
  • Chlorpheniramine; Dihydrocodeine; Pseudoephedrine
  • Chlorpheniramine; Guaifenesin; Hydrocodone; Pseudoephedrine
  • Chlorpheniramine; Hydrocodone
  • Chlorpheniramine; Hydrocodone; Phenylephrine
  • Chlorpheniramine; Hydrocodone; Pseudoephedrine
  • Chlorpheniramine; Phenylephrine
  • Chlorpheniramine; Pseudoephedrine
  • Chlorpromazine
  • Clemastine
  • Clomipramine
  • Clonazepam
  • Clorazepate
  • Clozapine
  • Codeine
  • Codeine; Guaifenesin
  • Codeine; Phenylephrine; Promethazine
  • Codeine; Promethazine
  • COMT inhibitors
  • Cyclizine
  • Cyproheptadine
  • Desipramine
  • Deutetrabenazine
  • Dexchlorpheniramine
  • Dexchlorpheniramine; Dextromethorphan; Pseudoephedrine
  • Dexmedetomidine
  • Dextromethorphan; Diphenhydramine; Phenylephrine
  • Dextromethorphan; Promethazine
  • Diazepam
  • Dihydrocodeine; Guaifenesin; Pseudoephedrine
  • Dimenhydrinate
  • Diphenhydramine
  • Diphenhydramine; Hydrocodone; Phenylephrine
  • Diphenhydramine; Ibuprofen
  • Diphenhydramine; Naproxen
  • Diphenhydramine; Phenylephrine
  • Disulfiram
  • Doxepin
  • Doxylamine
  • Doxylamine; Pyridoxine
  • Dronabinol
  • Droperidol
  • Enflurane
  • Entacapone
  • Esketamine
  • Estazolam
  • Eszopiclone
  • Ethanol
  • Etomidate
  • Ezetimibe; Simvastatin
  • Fentanyl
  • Fluoxetine; Olanzapine
  • Fluphenazine
  • Flurazepam
  • Fospropofol
  • Gabapentin
  • General anesthetics
  • Guaifenesin; Hydrocodone
  • Guaifenesin; Hydrocodone; Pseudoephedrine
  • Halothane
  • Homatropine; Hydrocodone
  • Hydrocodone
  • Hydrocodone; Ibuprofen
  • Hydrocodone; Phenylephrine
  • Hydrocodone; Potassium Guaiacolsulfonate
  • Hydrocodone; Potassium Guaiacolsulfonate; Pseudoephedrine
  • Hydrocodone; Pseudoephedrine
  • Hydromorphone
  • Hydroxyzine
  • Ibuprofen; Oxycodone
  • Imipramine
  • Isoflurane
  • Ketamine
  • Lasmiditan
  • Lemborexant
  • Levocetirizine
  • Levorphanol
  • Lofexidine
  • Lorazepam
  • Lumateperone
  • Maprotiline
  • Meclizine
  • Mepenzolate
  • Meperidine
  • Meperidine; Promethazine
  • Mephobarbital
  • Meprobamate
  • Mesoridazine
  • Methadone
  • Methohexital
  • Methscopolamine
  • Midazolam
  • Mirtazapine
  • Molindone
  • Morphine
  • Morphine; Naltrexone
  • Nabilone
  • Nalbuphine
  • Niacin; Simvastatin
  • Nortriptyline
  • Olanzapine
  • Oxazepam
  • Oxycodone
  • Oxymorphone
  • Pentazocine
  • Pentazocine; Naloxone
  • Pentobarbital
  • Perphenazine
  • Perphenazine; Amitriptyline
  • Phenobarbital
  • Phenothiazines
  • Phenylephrine; Promethazine
  • Pregabalin
  • Primidone
  • Prochlorperazine
  • Promethazine
  • Propofol
  • Protriptyline
  • Quazepam
  • Quetiapine
  • Remifentanil
  • Rufinamide
  • Secobarbital
  • Sedating H1-blockers
  • Sevoflurane
  • Simvastatin
  • Simvastatin; Sitagliptin
  • Sodium Oxybate
  • Sufentanil
  • Tapentadol
  • Temazepam
  • Thalidomide
  • Thiethylperazine
  • Thiopental
  • Thioridazine
  • Thiothixene
  • Tolcapone
  • Tramadol
  • Trazodone
  • Triazolam
  • Tricyclic antidepressants
  • Trifluoperazine
  • Trimipramine
  • Triprolidine
  • Zaleplon
  • Ziprasidone
  • Zolpidem

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