WPI 3968 is identified with Chlorzoxazone and is known to carry out its activities in the central nervous system to relax the skeletal muscle. Chemically it is also known as 5-Chloro-2-benzoxazolinone. As explained earlier, Chlorzoxazone relaxes the muscle and treats the discomfort resulting from acute or painful bone and muscle conditions.

Pharmacokinetics /Pharmacodynamics

  • Absorption: rapid
  • Metabolism: thoroughly hepatic via glucuronidation
  • Excretion: urine
  • The onset of action: within 1 hour
  • Time to peak: 1-2 hours
  • Duration of action: up to 6 hours
  • Half-life elimination: 1 hour
  • Chemical formula: C7H4O2
  • Molecular weight: 169.57


The ins and outs that define the WPI 3968 pill's specifications are;

Physical Characteristics

  • Physically Chlorzoxazone (WPI 3968 pill) is found to be,
  • As good as white
  • Virtually odorless
  • Crystalline powder


Chlorzoxazone is either soluble to a certain extent or slightly soluble in water. Also, comparatively soluble in alcohol, isopropyl alcohol, and methanol. At the same time, it is highly soluble in alkali hydroxides and ammonia solutions.


The WPI 3968 pill has an active ingredient named Chlorzoxazone, which carries inactive ingredients containing Docusate Sodium, Lactose (hydrous), Magnesium Stearate, Microcrystalline Cellulose, Pregelatinized Starch, Sodium Benzoate, and Sodium Starch Glycolate.

Clinical Pharmacology

Chlorzoxazone is a centrally-acting agent used for painful musculoskeletal conditions. According to studies based on humans and animals, it is found that Chlorzoxazone blocks the multisynaptic reflex arcs responsible for producing and sustaining the skeletal muscle spasm of varied etiology.

And it primarily performs its action by acting on subcortical areas of the brain and spinal cord. The consequence of this clinical effect results in the enhanced movement of muscles involved and pain relief via the reduction of skeletal muscle spasms. Furthermore, by administering Chlorzoxazone orally, in many people, it came to be known that the blood level of Chlorzoxazone could be attained in 30 minutes. It accomplished the peak level in about 1 to 2 hours.


Its metabolism is done quickly and excreted mainly in conjugated form as glucuronide through the urine. In addition, in 24 hours, the unchanged excreted dose of Chlorzoxazone is not more than 1 percent.


The primary use of Chlorzoxazone is to cure pain and stiffness produced by muscle sprains and strains. Furthermore, it is necessary to use the drug in combination with physical therapy, exercise, analgesics, and rest. Usually, chlorzoxazone tablets are taken three to four times daily by mouth or as prescribed by the doctor or pharmacist. It can be consumed with or without food. In addition, avoid the prolonged or more frequent use of this medicine, particularly the increase in the dose of Chlorzoxazone more than as prescribed by the doctor.


Before taking Chlorzoxazone:

It would be best if you told your doctor or pharmacist if,

  • You are allergic to Chlorzoxazone.
  • Taking prescription and nonprescription medicine, preferably sleeping pills, sedatives, tranquilizers, and vitamins.
  • Suffering from present or previous liver disease.
  • You are a pregnant woman planning to become pregnant or breastfeeding.
  • Your age is 65 years or older; you should ask your doctor because it is not safe or potent compared to other medications used for the same conditions.
  • The things that one should avoid after using WPI 3968 pill include the following;
  • Driving could be dangerous for you because it can cause drowsiness. And you should know about it.  
  • Avoid using Chlorzoxazone with alcohol because alcohol can worsen the side effects of Chlorzoxazone.

Dosage Form

Chlorzoxazone is available in capsule-shaped tablets of white color administered orally. Following are the available potencies of Chlorzoxazone: 250mg, 375mg, 500mg, and 750mg

The recommended dose of Chlorzoxazone in adults to treat musculoskeletal conditions is 250mg to 500mg 3 to 4 times a day orally. The amount starts with 500mg for more painful musculoskeletal conditions, which is increased to 750 mg 3 to 4 times daily. Besides that, decreasing the dose as the symptoms improve is preferable.

In geriatric patients, the use of Chlorzoxazone is prohibited. The dose of Chlorzoxazone to treat muscle spasms is 20mg/kg/day in 3 to 4 divided doses for adolescents and children.

Adverse Drug Reaction

The prolonged use of Chlorzoxazone can produce adverse reactions in the body, including effects on the central nervous system that lead to drowsiness, malaise, dizziness, and stimulation of the paradoxical central nervous system. In addition, it can cause urine discoloration, allergic skin rash, anaphylaxis, gastrointestinal bleeding, hepatotoxicity, and petechiae. WPI 3968 is not a controlled drug as per FDA and it is also not a narcotic substance. Combining with other sedatives and having addiction history chlorzoxazone can lead to high or euphoric feeling.

Side Effects

All medications have some pros and cons. Besides proper medication, WPI 3968 pill can produce unwanted effects that demand medical attention. Contact with doctor or pharmacist if you have felt any of these signs;

1- Fatigue, lack of appetite, dark urine, nausea, abdominal pain, light-colored stools, vomiting, and yellow skin. These symptoms are indications of liver problems.
2- It can cause significant reactions that signs such as wheezing, bad cough, fever, itching, seizures, and swelling of the face, lips, and tongue can determine.
3- Other side effects include; dizziness, feeling lightheaded, feeling discomfort or ill, overstimulation, fast heartbeats, nausea, vomiting, and constipation can commonly occur.
4- Rarely, it can cause bloody or black, tarry stools, severe stomach pain, shortness of breath, difficulty swallowing, and tightness in the chest.


If you take over a dose of Chlorzoxazone, it can cause severe and lethal side effects. Primarily cause nausea, vomiting or diarrhea, and drowsiness and dizziness that lead to gastrointestinal disturbance. Malaise and sluggishness subsequently, loss of muscle tone, and inability to make voluntary movements. Simultaneously, the absence of deep tendon reflex may be caused.


The overdose can be treated by gastric lavage and induction of emesis or administration of activated charcoal. Artificial respiration and oxygen should be employed if respiration is depressed.


Although some medications cannot be used together, in other circumstances, some medicines can be used together besides the interaction that might occur. In such cases, your doctor may adjust the dose or take other necessary precautions. WPI 3968 can also interact with other medicines. Please take care while using Chlorzoxazone with the below treatment.

  • Alfentanil
  • Amobarbital
  • Buprenorphine
  • Alprazolam
  • Bromazepam
  • Cetirizine
  • Clonazepam
  • Ketazolam
  • Lorazepam
  • Oxazepam
  • Morphine
  • Codeine


Chlorzoxazone tablets, USP, are available as oblong, scored, white tablets imprinted with WPI on one side and "39"-"68" on the other, thus packaged in bottles of 100 and 500. The storage temperature range of WPI 3968 is 20° to 25°C (68° to 77°F)

  • WPI 3968 Pill From Drugs.com accessed on 20.02.2023.
  •  Label: Chlorzoxazone from Dailymed accessed on 20.02.2023.
  • Chlorzoxazone | Cigna from cigna.com accessed on 19.02.2023


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