cyclobenzaprine (sye-kloe-ben-za-preen) Amrix, Flexeril

 Management of acute painful musculoskeletal conditions

associated with muscle spasm. Unlabeled Use:

Management of fibromyalgia.

Action

Reduces tonic somatic muscle activity at the level of the

brainstem. Structurally similar to tricyclic antidepressants.

Therapeutic Effects: Reduction in muscle

spasm and hyperactivity without loss of function.

Pharmacokinetics

Absorption: Well absorbed from the GI tract.

Distribution: Unknown.

Protein Binding: 93%.

Metabolism and Excretion: Mostly metabolized

by the liver.

Half-life: 1–3 days.

TIME/ACTION PROFILE (skeletal muscle

relaxation)

ROUTE ONSET PEAK† DURATION

PO within 1 hr 3–8 hr 12–24 hr

Extended release

unknown unknown 24 hr

†Full effects may not occur for 1–2 wk.

Contraindications/Precautions

Contraindicated in: Hypersensitivity; Should not

be used within 14 days of MAO inhibitor therapy; Immediate

period after MI; Severe or symptomatic cardiovascular

disease; Cardiac conduction disturbances; Hyperthyroidism.

Use Cautiously in: Cardiovascular disease; Geri:

Appears on Beers list. Poorly tolerated due to anticholinergic

effects; OB, Lactation, Pedi: Pregnancy, lactation,

and children 15 yr (safety not established).

Adverse Reactions/Side Effects

CNS: dizziness, drowsiness, confusion, fatigue, headache,

nervousness. EENT: dry mouth, blurred vision.

CV: arrhythmias. GI: constipation, dyspepsia, nausea,

unpleasant taste. GU: urinary retention.

Interactions

Drug-Drug: Additive CNS depression with other CNS

depressants, including alcohol, antihistamines,

opioid analgesics, and sedative/hypnotics. Additive

anticholinergic effects with drugs possessing anticholinergic

properties, including antihistamines,

antidepressants, atropine, disopyramide, haloperidol,

and phenothiazines. Avoid use within 14

days of MAO inhibitors (hyperpyretic crisis, seizures,

and death may occur). Drugs that affect serotonergic

neurotransmitter systems, including tricyclic antidepressants,

SSRIs, SNRIs, fentanyl, buspirone, tramadol,

and triptansqrisk of serotonin syndrome.

Drug-Natural Products: Concomitant use of

kava-kava, valerian, chamomile, or hops canq

CNS depression.

Route/Dosage

PO (Adults): Acute painful musculoskeletal conditions—

Immediate-release: 10 mg 3 times daily (range

20–40 mg/day in 2–4 divided doses; not to exceed 60

mg/day); Extended-release: 15–30 mg once daily. Fibromyalgia—

5–40 mg at bedtime (unlabeled).

Availability (generic available)

Tablets: 5 mg, 7.5mg, 10 mg. Cost: Generic—5 mg

$9.43/100, 10 mg $8.32/100. Extended-release

capsules (Amrix): 15 mg, 30 mg. Cost: All strengths

$1,437.60/60.