Cyclobenzaprine overdose

Spiller HA Cutino L. Fatal cyclobenzaprine overdose with postmortem values. J Forensic Sci. 2003 48 883-884. 

Common effects of cyclobenzaprine overdose were lethargy, agitation, sinus tachycardia, and both hypertension and hypotension (5). 

Cyclobenzaprine, a tricyclic amine structurally very similar to amitriptyline (see Figure 34-10), is used as a centrally acting skeletal muscle relaxant. Like amitriptyline, cyclobenzaprine causes sedation, produces central and peripheral muscarinic blockade, and potentiates adrenergic actions. In overdose, cyclobenzaprine may cause a typical anticholinergic toxidrome and cardiac arrhythmias, hypotension, and coma. However, cyclobenzaprine overdose is not as frequent nor as lethal as amitriptyline overdose. 

The most common CNS effects associated with cyclobenzaprine overdose are drowsiness and tachycardia. Less frequent manifestations include tremor, agitation, coma, ataxia, hypertension, slurred speech, confusion, dizziness, nausea, vomiting, and hallucinations. Rare but potentially critical manifestations of overdose are cardiac arrest, chest pain, cardiac dysrhythmias, severe hypotension, seizures, and neuroleptic malignant syndrome and stroke. Changes in the electrocardiogram, particularly in QRS axis or width, are clinically signilicant indicators of cyclobenzaprine toxicity. 

Tricyclic antidepressants are commoniy taken in overdose by suicidal patients and represent a major cause of poisoning hospitaiizations and deaths. Currently available tricyclic antidepressants are described in Table 11-7. Amitriptyline is also marketed in combination with chlordiazepoxide (Limbitrol ) or perphenazine (Etrafon or Tria-viF ). Cyclobenzaprine (FlexerilTW), a centrally acting muscle relaxant (see p 339), is structurally related to the tricyclic antidepressants but exhibits minimal cardiotoxic and variable CNS effects. Newer, noncyclic antidepressants are discussed on p 88. Monoamine oxidase inhibitors are discussed on page 269. 

B. Specific drugs and antidotes. There are no specific antidotes. Flumazenll (see p 446) Is a specific antagonist of benzodiazepine receptors, and would not be expected to cross-react with skeletal muscle relaxants or other sedative agents. While physostigmine may reverse anticholinergic symptoms associated with cyclobenzaprine and orphenadrine overdose. It Is not generally needed and may potentially cause seizures. 

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