CYCLOBENZAPRINE HYDROCHLORIDE

(sye-kloe-ben'za-preen)
Cycoflex, Flexeril
Classifications: autonomic nervous system agent; skeletal muscle relaxant, central acting
Pregnancy Category: B

Availability

5 mg, 10 mg tablets

Actions

Structurally and pharmacologically related to tricyclic antidepressants. Relieves skeletal muscle spasm of local origin without interfering with muscle function. Believed to act primarily within CNS at brain stem; some action at spinal cord level is also probable. Depresses tonic somatic motor activity, although both gamma and alpha motor neurons are affected.

Therapeutic Effects

In common with other tricyclic compounds, it increases circulating norepinephrine by blocking its synaptic reuptake, thus producing its antidepressant effect. Also has sedative effects and potent central and peripheral anticholinergic activity.

Uses

Short-term adjunct to rest and physical therapy for relief of muscle spasm associated with acute musculoskeletal conditions. Not effective in treatment of spasticity associated with cerebral palsy or cerebral or cord disease.

Contraindications

Acute recovery phase of MI, patients with cardiac arrhythmias, heart block or conduction disturbances, CHF, hyperthyroidism. Use for periods longer than 2 or 3 wk not recommended by manufacturer. Pregnancy (category B), lactation. Safe use in children <15 y not established.

Cautious Use

Patients receiving anticholinergic medications; prostatic hypertrophy, history of urinary retention, angle-closure glaucoma; increased IOP, seizures; cardiovascular disease; hepatic impairment; older adults, debilitated patients; history of psychiatric illness.

Route & Dosage

Muscle Spasm
Adult: PO 5–10 mg t.i.d. (max: 60 mg/d)
Geriatric: Start with 5 mg

Mild Hepatic Impairment
Start with 5 mg

Moderate to Severe Hepatic Impairment
Not recommended

Administration

Oral

Do not administer drug if patient is receiving an MAO INHIBITOR (e.g., furazolidone, isocarboxazid, pargyline, tranylcypromine).
Cyclobenzaprine is intended for short-term (2 or 3 wk) use.
Store in tightly closed container, preferably at 15°–30° C (59°–86° F) unless otherwise directed by manufacturer.

Adverse Effects (1%)

Body as a Whole: Edema of tongue and face, sweating, myalgia, hepatitis, alopecia. Shares toxic potential of tricyclic antidepressants. CV: Tachycardia, syncope, palpitation, vasodilation, chest pain, orthostatic hypotension, dyspnea; with high doses, possibility of severe arrhythmias. GI: Dry mouth, indigestion, unpleasant taste, coated tongue, tongue discoloration, vomiting, anorexia, abdominal pain, flatulence, diarrhea, paralytic ileus. CNS: Drowsiness, dizziness, weakness, fatigue, asthenia, paresthesias, tremors, muscle twitching, insomnia, euphoria, disorientation, mania, ataxia. Skin: Pruritus, urticaria, skin rash. Urogenital: Increased or decreased libido, impotence.

Interactions

Drug: Alcohol, barbiturates, other cns depressants enhance CNS depression; potentiates anticholinergic effects of phenothiazine and other anticholinergics; mao inhibitors may precipitate hypertensive crisis—use with extreme caution.

Pharmacokinetics

Absorption: Well absorbed from GI tract with some first-pass elimination in liver. Onset: 1 h. Peak: 3–8 h. Duration: 12–24 h. Distribution: Highly protein bound (93%). Metabolism: Metabolized in liver to inactive metabolites. Elimination: Slowly excreted in urine with some elimination in feces; may be excreted in breast milk. Half-Life: 1–3 d.

Nursing Implications

Assessment & Drug Effects

Supervision of ambulation may be indicated, especially in the older adult because of risk of drowsiness and dizziness.
Withhold drug and notify physician if signs of hypersensitivity, e.g., pruritus, urticaria, rash, appear.

Patient & Family Education

Avoid driving and other potentially hazardous activities until reaction to drug is known. Adverse effects include drowsiness and dizziness.
Avoid alcohol and other CNS DEPRESSANTS (unless otherwise directed by physician) because cyclobenzaprine enhances their effects.
Dry mouth may be relieved by increasing total fluid intake (if not contraindicated).
Keep physician informed of therapeutic effectiveness. Spasmolytic effect usually begins within 1 or 2 d and may be manifested by lessening of pain and tenderness, increase in range of motion, and ability to perform ADL.
Do not breast feed while taking this drug.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug