Chlorzoxazone

Pronunciation: klor-ZOX-uh-zone
Class: Skeletal muscle relaxant, centrally acting

Trade Names

Paraflex
- Caplets 250 mg

Parafon Forte DSC
- Caplets 500 mg

Remular-S
- Tablets 250 mg

Pharmacology

Action may be related to its sedative properties or to inhibition of reflex arcs at spinal cord and subcortical levels of brain.

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Pharmacokinetics

Absorption

T _max is 1 to 2 h.

Metabolism

Rapidly metabolized.

Elimination

Excreted in the urine as glucuronide conjugate. Less than 1% is excreted in the urine as unchanged drug. The t _½ is about 60 min.

Onset

1 h.

Duration

3 to 4 h.

Indications and Usage

Relief of discomfort associated with painful musculoskeletal conditions.

Contraindications

Standard considerations.

Dosage and Administration

PO Initial (for acute pain): 500 mg 3 or 4 times daily; increase to 750 mg if needed. As improvement occurs, reduce dose; 250 mg 3 or 4 times daily is usually sufficient.

General Advice

Give with meals to avoid GI upset.

Drug Interactions

Additive CNS depressant effects may occur.

Laboratory Test Interactions

None well documented.

Adverse Reactions

CNS

Drowsiness; dizziness; lightheadedness; malaise; overstimulation.

Dermatologic

Allergic-type skin rashes; petechiae.

GI

GI disturbances.

Genitourinary

Urine discoloration (orange or purple red).

Hepatic

Drug-induced hepatitis.

Miscellaneous

Hypersensitivity (eg, angioneurotic edema; anaphylaxis).

Precautions

Pregnancy

Pregnancy category undetermined.

Lactation

Undetermined.

Hepatic Function

Avoid use in patients with liver impairment; discontinue if signs of dysfunction occur.

Hazardous Tasks

May impair ability to perform tasks requiring mental or physical coordination or dexterity, including driving. Drowsiness is very common.

Overdosage

Symptoms

Nausea, vomiting, diarrhea, drowsiness, dizziness, lightheadedness, malaise, sluggishness, loss of muscle tone, decreased deep tendon reflex, respiratory depression.

Patient Information

• Instruct patient to inform health care provider of any urticaria, redness or itching.
• Tell patient to report to health care provider any yellowing of skin or eyes.
• Advise patient that drug may cause drowsiness and to use caution while driving or performing other tasks that require mental alertness.
• Advise patient to avoid intake of alcoholic beverages and other medications that cause drowsiness while taking product.
• Advise patient to notify health care provider before discontinuing medication.
• Inform patient to take a missed dose as soon as possible, unless several hours have passed. Advise patient not to double doses.
• Inform patient urine may turn orange or purple-red while taking this medication.
• Instruct patient to take with meals to avoid GI upset.

Copyright © 2009 Wolters Kluwer Health.