INN monograph
Chlorzoxazone
Muscle Relaxant [EPC] · POM
Source-linked · Updated 03 Aug 2026 · Source: FDA drug label via OpenFDA/DailyMed; Local active-ingredient clinical extract; Professional class pharmacology (Therapeutic agent (verify pharmacological class))
Kenya market
Wholesale / list prices where loaded
Risk first
Contraindications
- Hypersensitivity to the active substance or excipients.
- Additional absolute contraindications are indication- and product-specific — consult SmPC.
Precautions
- WARNINGS Serious (including fatal) hepatocellular toxicity has been reported rarely in patients receiving chlorzoxazone.
- 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.
- Chlorzoxazone should be discontinued immediately and a physician consulted if any of these signs or symptoms develop.
- Chlorzoxazone use 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.
- Usage in Pregnancy The safe use of chlorzoxazone has not been established with respect to the possible adverse effects upon fetal development.
- Therefore, it should be used in women of childbearing potential only when, in the judgment of the physician, the potential benefits outweigh the possible risks.
Point of care
Dosing
Adult
DOSAGE AND ADMINISTRATION Usual Adult Dosage One tablet three or four times daily. If adequate response is not obtained with this dose, it may be increased to one and one-half tablets (750 mg) three or four times daily. As improvement occurs dosage can usually be reduced.
Paediatric
See label paediatric section if present; otherwise use paediatric formulary — do not extrapolate adult doses.
Renal
Review renal impairment dosing; many agents need CrCl/eGFR adjustment.
- CrCl 0–120: Confirm renal dosing in product SmPC / primary label.
Hepatic
Review hepatic impairment dosing; monitor LFTs if agent is hepatically cleared or hepatotoxic.
Safety
Drug interactions
- Professional use: confirm indication, dose, duration, monitoring and patient counselling points against current Kenya STG / EML and the product SmPC.
- Document allergy status and key interactions.
Safety
Adverse effects
- ADVERSE REACTIONS Chlorzoxazone containing products are usually well tolerated.
- It is possible in rare instances that chlorzoxazone may have been associated with gastrointestinal bleeding.
- Drowsiness, dizziness, lightheadedness, malaise, or over-stimulation may be noted by an occasional patient.
- Rarely, allergic type skin rashes, petechiae, or ecchymoses may develop during treatment.
- Angioneurotic edema or anaphylactic reactions are extremely rare.
- There is no evidence that the drug will cause renal damage.
- Rarely, a patient may note discoloration of the urine resulting from a phenolic metabolite of chlorzoxazone.
- This finding is of no known clinical significance.
- To report SUSPECTED ADVERSE EVENTS, contact Aurobindo Pharma USA, Inc. at 1-866-850-2876 or FDA at 1-800- FDA-1088 or http://www.fda.gov/ for voluntary reporting of adverse reactions.
Use
Indications
- INDICATIONS Chlorzoxazone is indicated as an adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions.
- The mode of action of this drug has not been clearly identified, but may be related to its sedative properties.
- Chlorzoxazone does not directly relax tense skeletal muscles in man.
Pharmacology
Mode of action
Mechanism is agent-specific.
Full mechanism text
Mechanism is agent-specific. At receptor, enzyme, ion channel, transporter or microbial target level, the drug alters a physiological or pathological pathway to produce its therapeutic effect. Confirm precise molecular mechanism in current SmPC / pharmacology reference for this INN before high-stakes decisions.
ADME
Pharmacokinetics & PD
| Onset | Product-specific |
|---|---|
| Duration | Product-specific |
| Route | See product SmPC |
Full PK/PD text
CLINICAL PHARMACOLOGY Chlorzoxazone is a centrally-acting agent for painful musculoskeletal conditions. Data available from animal experiments as well as human study indicate that chlorzoxazone acts primarily at the level of the spinal cord and subcortical areas of the brain where it inhibits multisynaptic reflex arcs involved in producing and maintaining skeletal muscle spasm of varied etiology. The clinical result is a reduction of the skeletal muscle spasm with relief of pain and increased mobility of the involved muscles. Blood levels of chlorzoxazone can be detected in people during the first 30 minutes and peak levels may be reached, in the majority of the subjects, in about 1 to 2 hours after oral administration of chlorzoxazone. Chlorzoxazone is rapidly metabolized and is excreted in the urine, primarily in a conjugated form as the glucuronide. Less than one percent of a dose of chlorzoxazone is excreted unchanged in the urine in 24 hours.
Kenya
Brands & prices
| Brand | Company | Pack | KES |
|---|---|---|---|
| No brands linked yet. | |||
Special populations
Pregnancy & lactation
Pregnancy
Use only if potential benefit justifies potential risk; prefer agents with better reproductive data when alternatives exist.
Lactation
Assess infant risk vs benefit of maternal therapy; prefer agents with lactation data.
Diet
Food & alcohol
- Food
- Food
Trust
Sources & disclaimer
Source: FDA drug label via OpenFDA/DailyMed; Local active-ingredient clinical extract; Professional class pharmacology (Therapeutic agent (verify pharmacological class))
Clinical review date not recorded.
Decision support only — not a substitute for clinical judgment, product SmPC, or Kenya STG/EML.