chlorzoxazone

Action

Unclear. Thought to act on spinal cord and subcortical levels of brain, inhibiting multisynaptic reflex arcs responsible for skeletal muscle activity.

Availability

Caplets: 500 mg

Tablets: 250 mg, 500 mg

Indications and dosages

➣ Adjunct to rest and physical therapy in treatment of muscle spasms associated with acute, painful musculoskeletal conditions

Adults: 250 to 750 mg P.O. three to four times daily

Contraindications

• Hypersensitivity to drug

• Hepatic impairment

Precautions

Use cautiously in:

• underlying cardiovascular disease, renal impairment

• children (safety not established).

Administration

• If desired, crush tablets and mix contents with food or water.

• Don't withdraw drug abruptly.

Adverse reactions

CNS: dizziness, drowsiness, light-headedness, malaise, headache, over-stimulation, tremor

GI: nausea, vomiting, constipation, diarrhea, heartburn, abdominal distress, anorexia

GU: orange or purplish-red urine

Hepatic: hepatic dysfunction

Skin: allergic dermatitis, urticaria, erythema, pruritus, petechiae, ecchymosis, angioedema

Other: allergic reactions

Interactions

Drug-drug. CNS depressants (including antihistamines, antidepressants, opioids, sedative-hypnotics): increased risk of CNS depression

Drug-diagnostic tests. Alanine aminotransferase, alkaline phosphatase, bilirubin: increased levels

Drug-herbs. Chamomile, hops, kava, skullcap, valerian: increased CNS depression

Drug-behaviors. Alcohol use: increased sedation

Patient monitoring

☞ Stay alert for signs and symptoms of hepatic dysfunction. Withhold drug and notify prescriber if these occur.

• Monitor hepatic enzyme and serum electrolyte levels.

Patient teaching

☞ Instruct patient to promptly report yellowing of eyes or skin.

• Caution patient not to consume alcohol during therapy.

• Instruct patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.

• Tell patient that drug may turn his urine orange or purplish-red.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, herbs, and behaviors mentioned above.