Source: Health Products and Food Branch (CA) Revision Year: 2020
Flexeril (cyclobenzaprine hydrochloride) is indicated as an adjunct to rest and physical therapy for relief of muscle spasm associated with acute, painful musculoskeletal conditions.
Flexeril should be used only for short periods (up to two or three weeks), because adequate evidence of effectiveness for more prolonged use is not available, and because muscle spasm associated with acute, painful musculoskeletal conditions is generally of short duration and specific therapy for longer periods is seldom warranted.
Cyclobenzaprine hydrochloride has not been found effective in the treatment of spasticity associated with cerebral or spinal cord disease, or in children with cerebral palsy.
Evidence from clinical studies suggests that use in the geriatric population is associated with differences in safety or effectiveness (see DOSAGE AND ADMINISTRATION and ACTION AND CLINICAL PHARMACOLOGY – Pharmacokinetics, Elderly).
The safety and effectiveness of cyclobenzaprine hydrochloride in children below 15 years of age have not been established.
Cyclobenzaprine hydrochloride is not recommended for periods longer than two or three weeks (see INDICATIONS AND CLINICAL USE).
Reduced (e.g. less frequent) dosing should be considered for patients who are elderly (>65 years of age) or have mild hepatic impairment (see WARNINGS AND PRECAUTIONS – Special Populations, and ACTION AND CLINICAL PHARMACOLOGY – Pharmacokinetics – Special Populations and Conditions).
The usual dosage of Flexeril (cyclobenzaprine hydrochloride) is 10 mg three times a day, with a range of 20 to 40 mg a day in divided doses. Dosage should not exceed 60 mg a day.
Signs and symptoms of toxicity may develop rapidly after cyclobenzaprine overdose; hospital monitoring is required as soon as possible. Monitor patients for an extended period after ingestion as delayed absorption may occur due to the anticholinergic effects of cyclobenzaprine.
Based on the known pharmacologic actions of the drug, overdosage may cause drowsiness, agitation, tachycardia and other cardiac rhythm abnormalities such as bundle branch block, ECG evidence of impaired conduction, and congestive heart failure. Other manifestations of high doses may be dilated pupils, severe hypotension, temporary confusion, disturbed concentration, transient visual hallucinations, stupor, coma , hyperactive reflexes, muscle rigidity, convulsions, vomiting, or hyperpyrexia, in addition to anything listed under ADVERSE REACTIONS. Changes in the electrocardiogram, particularly in QRS axis or width, are clinically significant indicators of cyclobenzaprine toxicity.
There are no specific antidotes. Treatment is symptomatic and supportive. Obtain an ECG, and initiate cardiac monitoring and observation for signs of hypotension, CNS or respiratory depression, or seizures.
Maintain an open airway, adequate fluid intake, and regulation of body temperature. Standard medical measures should be used to manage circulatory shock and metabolic acidosis.
If early in therapy, empty the stomach as quickly as possible. The suitability of emesis, gastric lavage and activated charcoal for gastric decontamination depends upon the time since ingestion and upon the patient being asymptomatic, conscious and cooperative. These processes should be considered early in therapy, before absorption is complete. Absorption may be delayed due to the anticholinergic effects of cyclobenzaprine. Gastric decontamination should not delay hospitalization.
Dialysis is probably of no value due to low plasma concentrations of the drug.
An ECG should be taken and cardiac function closely monitored if there is any evidence of dysrhythmia. Close monitoring of cardiac function for not less than five days is advisable.
Serum alkalinization, to a pH of 7.45 to 7.55, using intravenous sodium bicarbonate therapy/hyperventilation should be instituted for patients with dysrhythmias and/or QRS widening. Many antiarrhythmics are contraindicated; consult a poison control centre for current approaches to refractory dysrhythmia.
In patients with CNS depression, early intubation is advised because of the potential for abrupt deterioration. Anticonvulsants (e.g. benzodiazepines) may be given to control seizures. Consult a poison control centre if considering the use of physostigmine to treat life-threatening symptoms of cyclobenzaprine overdose that have been unresponsive to other therapies.
Since overdosage is often deliberate, patients may attempt suicide by other means during the recovery phase.
Deaths by deliberate or accidental overdosage have occurred with this class of drugs.
For management of a suspected drug overdose, contact your regional Poison Control Centre immediately.
Store at room temperature between 15°-30°C in tightly sealed containers. Protect from heat.
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