Get your patient on Chlorzoxazone - Chlorzoxazone tablet (Chlorzoxazone)

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.

Usual Adult Dosage

Chlorzoxazone tablets USP, 375 mg:

One tablet three or four times daily. If adequate response is not obtained with this dose, the 375 mg tablets may be increased to two tablets (750 mg) three or four times daily. As improvement occurs dosage can usually be reduced.

Chlorzoxazone tablets USP, 500 mg:

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.

Chlorzoxazone tablets USP, 750 mg:

1/3 tablet (250 mg) three or four times daily. Initial dosage for painful musculoskeletal conditions should be 2/3 tablet (500 mg) three or four times daily. If adequate response is not obtained with this dose, it may be increased to one tablet (750 mg) three or four times daily. As improvement occurs dosage can usually be reduced.

Chlorzoxazone is contraindicated in patients with known intolerance to the drug.

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.

Each 375 mg chlorzoxazone tablet contains: Chlorzoxazone USP 375 mg.

Each 500 mg chlorzoxazone tablet contains: Chlorzoxazone USP 500 mg.

Each 750 mg chlorzoxazone tablet contains: Chlorzoxazone USP 750 mg.

Chemical Name: 5-Chloro-2-benzoxazolinone.

Structural Formula:

Molecular Formula: C ₇ H ₄ ClNO ₂

Molecular Weight: 169.56

Chlorzoxazone, USP is a white or practically white, practically odorless, crystalline powder. Chlorzoxazone USP is slightly soluble in water; sparingly soluble in alcohol, in isopropyl alcohol, and in methanol; soluble in solutions of alkali hydroxides and ammonia.

Inactive ingredients:

375 mg contains colloidal silicon dioxide, corn starch, croscarmellose sodium, docusate sodium with sodium benzoate, lactose monohydrate, magnesium stearate and microcrystalline cellulose.

500 mg contains D&C Red 27/Phloxine Aluminium lake, FD&C Yellow 6/Sunset Yellow FCF Aluminium lake, hypromellose, lactose monohydrate, magnesium stearate, microcrystalline cellulose, polysorbate 80, pregelatinized starch, sodium starch glycolate.

750 mg contains colloidal silicon dioxide, corn starch, croscarmellose sodium, docusate sodium with sodium benzoate, lactose monohydrate, magnesium stearate and microcrystalline cellulose.

Meets USP dissolution test 5 for 500 mg.

FDA approved dissolution method differs from that of the USP for 375 mg and 750 mg.

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.

Chlorzoxazone tablets USP are supplied as follows:

375 mg

A white to off-white capsule shaped tablet debossed with “N” on one side and “375” on other side.

Bottles of 100                                                  NDC 59651-305-01

500 mg

A light orange to orange round shaped, flat hexagonal, beveled debossed with “N” on one side of break line and “500” on other side of break line and plain on other side.

Bottles of 100 with child-resistant closure     NDC 59651-306-01

Bottles of 500                                                 NDC 59651-306-05

750 mg

A white to off-white capsule shaped tablet debossed with “N” on one side with trisect and “750” on other side with bisect.

Bottles of 100                                                 NDC 59651- 307-01

Dispense in tight container as defined in the official compendium.

Store at 20° to 25° C (68° to 77° F) [see USP Controlled Room Temperature].

Distributed by:
Aurobindo Pharma USA, Inc.
279 Princeton-Hightstown Road
East Windsor, NJ 08520

Manufactured by:
Aurobindo Pharma Limited
Hyderabad-500 032, India

Revised: 09/2023