Class: Skeletal muscle relaxant, centrally acting
- Capsules, extended-release 15 mg
- Capsules, extended-release 30 mg
- Tablets 7.5 mg
- Tablets 5 mg
- Tablets 10 mg
Mechanism of Action
Relieves skeletal muscle spasms of local origin without interfering with muscle function by acting within CNS at brain stem. Structurally and pharmacologically related to tricyclic antidepressants.
Mean oral bioavailability ranges from 33% to 55%. Reaches steady state in approximately 3 to 4 days following 3-times-daily dosing. C max is approximately 12.8 to 46.1 ng/mL and AUC is approximately 80 to 319 ng•h/mL.Extended-release (ER)
T max is 7 to 8 h. C max is 8 to 20 ng/mL. AUC is 354 to 780 ng•h/mL.
Highly bound to plasma proteins.
Extensively metabolized, primarily to glucuronide-like conjugates.
Excreted primarily via kidneys. The t ½ is approximately 8 to 37 h.ER
The t ½ is approximately 33 h.
12 to 24 h.
Indications and Usage
Relief of muscle spasms associated with acute painful musculoskeletal conditions.
Treatment of fibrositis.
Standard considerations; use of MAOIs or within 14 days of their discontinuation; acute recovery phase of MI; arrhythmias; heart block or conduction disturbances; CHF; hyperthyroidism.
Dosage and AdministrationAdults
5 to 10 mg 3 times daily.ER
15 to 30 mg once daily.
- Do not use longer than 3 wk.
Store at 59° to 86°F.
Drug InteractionsAlcohol and other CNS depressants
May cause additive CNS depression.MAOIs
May cause hyperpyretic crisis, severe seizures, and death.
Laboratory Test Interactions
None well documented.
Palpitations (6%); arrhythmia, hypotension, syncope, tachycardia, vasodilation (postmarketing).
Somnolence (100%); drowsiness (39%); dizziness (19%); headache (17%); attention disturbance, tremor (6%); fatigue (3%); decreased mental acuity, irritability, nervousness (1% to 3%); abnormal sensations, abnormal thinking, agitation, anxiety, ataxia, depression, disorientation, dreaming, dysarthria, excitement, hallucinations, hypertonia, insomnia, malaise, paresthesia, psychosis, seizures, vertigo (postmarketing).
Acne (6%); sweating (postmarketing).
Dry throat (8%); blurred vision (3%); pharyngitis (1% to 3%); ageusia, diplopia, tinnitus (postmarketing).
Dry mouth (58%); nausea (8%); dysgeusia (6%); dyspepsia (4%); constipation (3%); abdominal pain, acid regurgitation, diarrhea (1% to 3%); anorexia, flatulence, gastritis, GI pain, thirst, tongue edema, vomiting (postmarketing).
Urinary frequency, urinary retention (postmarketing).
Abnormal liver function, cholestasis, hepatitis, jaundice (postmarketing).
Anaphylaxis (including angioedema), facial edema, pruritus, rash, urticaria (postmarketing).
Local weakness, muscle twitching (postmarketing); myalgia.
Category B .
Safety and efficacy in children younger than 15 yr of age not established.
Do not use ER in elderly patients.
Do not administer ER to patients with hepatic function impairment.
Use with caution in patients with angle-closure glaucoma, increased IOP, and urinary retention.
Agitation, arrhythmia, ataxia, cardiac arrest, cardiac dysrhythmias, chest pain, CHF, coma, confusion, dilated pupils, dizziness, drowsiness, ECG changes (particularly in QRS axis), hyperactive reflexes, hyperpyrexia, hypertension, hypotension, hypothermia, nausea, neuroleptic malignant syndrome, seizures, slurred speech, stupor, tachycardia, tremor, visual hallucinations, vomiting.
- Inform patient that this medication makes injury temporarily feel better. Caution patient not to rush recovery and to avoid lifting or exercising too soon, which may damage muscles further.
- Caution patient to rise slowly from a sitting or standing position to avoid injury.
- Instruct patient to report the following symptoms to health care provider: confusion, difficulty urinating, fever, heart irregularities, palpitations, shortness of breath, weight gain, or yellowing of skin or eyes.
- Advise patient to take sips of water frequently, suck on ice chips or sugarless hard candy, or chew sugarless gum if dry mouth occurs.
- Instruct patient to avoid alcoholic beverages or other CNS depressants while taking this medicine.
- Advise patient that drug may cause drowsiness and to use caution while driving or performing other tasks requiring mental alertness.