Cyclobenzaprine

Oral
Painful muscle spasm associated with musculoskeletal conditions

MIld: Start with 5 mg dose with less frequent dosing. Moderate to severe: Not recommended.

Recent MI, arrhythmias, severe liver disease.

Cardiac disease, history of epilepsy, hepatic impairment, hyperthyroidism, pheochromocytoma, history of mania, psychoses, close-angle glaucoma, history of urinary retention, concurrent electroconvulsive therapy, diabetes. Pregnancy and lactation; elderly, child. Unsafe for use in patients with porphyria. Avoid abrupt withdrawal. May cause drowsiness; do not drive or operate machinery. Treatment for more than 2-3 wk is not recommended.

Antimuscarinic effects, neurological adverse effects, GI disorders, orthostatic hypotension, tachycardia, hypersensitivity reactions. Rarely, cholestatic jaundice and blood disorders. Endocrine effects, sexual dysfunction, changes in blood sugar. Increased appetite with wt gain, sweating.

PO: B

Drowsiness, tachycardia, tremor, agitation, coma, ataxia, hypertension, slurred speech, confusion, dizziness, nausea, vomiting, and hallucinations, cardiac arrest, chest pain, cardiac dysrhythmias, changes in the electrocardiogram, particularly in QRS axis or width, severe hypotension, seizures, and neuroleptic malignant syndrome. Emesis or gastric lavage followed by activated charcoal. Treatment is symptomatic and supportive with monitoring of ECG and observing for signs of CNS or respiratory depression, hypotension, cardiac dysrhythmias and/or conduction blocks and seizures. For patients with with dysrhythmias and/or QRS widening, use IV sodium bicarbonate and hyperventilationv to correct pH to 7.45 to 7.55. Dysrhythmias unresponsive to sodium bicarbonate therapy/hyperventilation may respond to lidocaine, bretylium or phenytoin but type 1A and 1C antiarrhythmics are generally contraindicated. Seizures may be controlled with benzodiazepines or, if ineffective, other anticonvulsants (e.g. phenobarbital, phenytoin) may be used. Monitoring of plasma drug levels should not guide management of the patient and dialysis is probably of no value because of low plasma concentrations of the drug. Consult local poison centre for latest treatment infomation.

Plasma concentration may be increased with the use of cimetidine, diltiazem, disulfiram, methylphenidate, ritonavir, and verapamil. Side-effects are increased by adrenaline, amiodarone, general anesthetics, SSRIs, antihistamines, antimuscarinics, antipsychotics, anxiolytics and hypnotics, clozapine, disopyramide, diuretics, flecainide, MAOIs, moclobemide, moxifloxacin, nefopam, nicorandil, noradrenaline, phenothiazine, pimozide, procainamide, propafenone, quinidine, selegiline, sibutramine, sotalol, terfenadine, thioridazine, and tramadol. Effects of adrenergic neurone blockers, clonidine, barbiturates, nitrates, and primidone are reduced while effects of baclofen, opioid analgesics, and thyroid hormones are enhanced with concomitant use of cyclobenzaprine. Carbamazepine and rifampicin may increase metabolism of cyclobenzaprine. Effects may be antagonized by oestrogens. Avoid use with brimonidine, entacapone, artemether with lumefantrine, or sibutramine. CNS effects may be enhanced by other CNS depressants.

Description:
Mechanism of Action: Cyclobenzaprine, a centrally-acting skeletal muscle relaxant, is structurally related to tricyclic antidepressants, thus they share similar properties. It acts on the brain stem, decreasing tonic-somatic motor activities influencing both the α and δ motor systems. It is used as an adjunct in the symptomatic treatment of painful muscle spasms associated with musculoskeletal conditions.
Onset: 1 hr.
Duration: 12-24 hr.
Pharmacokinetics:
Absorption: Readily and almost completely absorbed from the GI tract.
Distribution: Protein binding: About 93%.
Metabolism: Largely metabolised, mainly to glucuronide conjugates.
Excretion: Mainly excreted in urine. Some unchanged drug is removed in the bile and faeces.

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