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Pharmacologic class: Autonomic nervous system drug
Therapeutic class: Skeletal muscle relaxant (centrally acting)
Pregnancy risk category B
Unclear. Thought to act primarily at brain stem (and to a lesser extent at spinal cord level) to relieve skeletal muscle spasms of local origin without altering muscle function.
Capsules (extended-release): 15 mg, 30 mg
Tablets: 5 mg, 7.5 mg, 10 mg
Indications and dosages
➣ Adjunct to rest and physical therapy to relieve muscle spasm associated with acute, painful musculoskeletal conditions
Adults: 5 mg P.O. t.i.d. (immediate-release tablet). May increase to 10 mg P.O. t.i.d. (immediate-release tablet) as needed. Or, 15 mg (extended-release capsule) P.O. daily; some patients may need up to 30 mg/day, given as one 30-mg (extended-release capsule) P.O. daily or two 15-mg (extended-release capsules) P.O. daily.
• Hypersensitivity to drug
• Acute recovery phase after myocardial infarction (MI)
• Heart failure
• MAO inhibitor use within past 14 days
Use cautiously in:
• cardiovascular disease, closed-angle glaucoma, hepatic impairment, increased intraocular pressure, urinary retention
• elderly patients
• pregnant or breastfeeding patients
• children younger than age 15.
☞ Don't give within 14 days of MAO inhibitor. Drug interaction may cause hypertensive crisis and severe seizures.
• Give extended-release capsule at approximately the same time each day.
• Know that drug shouldn't be used for more than 3 weeks.
• Be aware that drug may not be first-line agent for elderly patients because of its anticholinergic effects.
CNS: dizziness, drowsiness, syncope, confusion, fatigue, headache, nervousness, decreased mental acuity, irritability, weakness, insomnia, depression, disorientation, delusions, peripheral neuropathy, abnormal gait, Bell's palsy, EEG changes, extrapyramidal symptoms, cerebrovascular accident
CV: vasodilation, tachycardia, chest pain, hypotension, MI, heart block
EENT: blurred vision
GI: nausea, constipation, dyspepsia, swollen parotid glands, mouth inflammation, discolored tongue, dry mouth, paralytic ileus
GU: galactorrhea, urinary retention, urinary frequency, gynecomastia, testicular swelling, libido changes, erectile dysfunction
Hematologic: purpura, eosinophilia, bone marrow depression, leukopenia, thrombocytopenia
Metabolic: hyperglycemia, hypoglycemia, syndrome of inappropriate diuretic hormone secretion
Musculoskeletal: muscle ache
Skin: photosensitization, alopecia, angioedema
Other: unpleasant taste, weight gain or loss, edema
Drug-drug. Anticholinergics, anti-cholinergic-like drugs (including anti-depressants, antihistamines, disopyramide, haloperidol, phenothiazines): additive anticholinergic effects
Antihistamines, CNS depressants, opioids, sedative-hypnotics: additive CNS depression
Guanadrel, guanethidine: reduction in or blockage of these drugs' actions
MAO inhibitors: hyperpyretic crisis, seizures, death
Drug-herbs. Chamomile, hops, kava, skullcap, valerian: increased CNS depression
Drug-behaviors. Alcohol use: increased CNS depression
• Assess for adverse CNS effects, such as drowsiness, dizziness, and decreased mental acuity.
• Monitor patient for evidence of drug interactions, especially when giving drug with CNS depressants.
• Tell patient to take extended-release capsule at approximately the same time each day.
• Tell patient that drug may cause dry mouth.
• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration, alertness, and vision.
• Advise patient not to use alcohol, sedatives, pain medications, over-the-counter preparations, or herbs without consulting prescriber.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, herbs, and behaviors mentioned above.