Cyclobenzaprine (proheptatriene, dimethylpropylamine) is a
synthetic chemical, and is a tricyclic amine similar in structure and action to
amitriptyline. It is sometimes used in the treat- ment of acute skeletal muscle
spasm. Therapeutic doses range from 30 to 60 mg/day in adults. It should only
be used for short periods (up to two or three weeks). The major metabolites of
cyclobenzaprine include amitriptyline, norcyclobenzaprine and nortriptyline.
Adverse effects are anticholinergic in nature comprising
mydriasis, warm, dry, flushed skin, dry mouth, urinary retention,
disorientation, and sometimes convulsions. These symptoms become more
pronounced in overdose, and in addition, the following manifestations are seen
: urinary retention, tachycardia, delirium, hallucinations, hypotension (rarely
hypertension), respiratory depression, and cardiac arrhythmias.
The CNS depressant effects of cyclobenzaprine are enhanced
when it is coingested with other CNS depressant drugs (benzodi- azepines,
opioids, barbiturates, ethanol, sedative hypnotics, etc.).Concomitant
cyclobenzaprine and anticholinergic therapy may result in additive
anticholinergic effects. Concomitant mono- amine oxidase (MAO) inhibitor and
cyclobenzaprine therapy may result in hyperpyrexia, excitation, and seizures.
Treatment is on similar lines as for tricyclic overdose.
Gastric lavage is said to be beneficial upto several hours after ingestion.
Serious symptoms may necessitate the use of physostigmine (1 to 4 mg IV slowly,
over 5 to 10 minutes). If the heart rate exceeds 160 beats/minute and/or the
patient demonstrates evidence of haemodynamic instability with central
anticholinergic symptoms, treatment with phys- ostigmine may be necessary.
Teratogenicity has been reported following first trimester
maternal exposure to cyclobenzaprine. A syndrome of imper- forate oropharynx
with costovertebral and auricular anomalies was reported in a child of 32-week
gestation following first trimester maternal ingestion of cyclobenzaprine and
Accidental overdose involving these
drugs is not uncommon. Suicides have been reported with many of these drugs,
and most of them have involved medical or paramedical personnel.
Homicides are increasingly being
reported, especially with reference to neuromuscular blocking agents. There is
even a report of a serial murder involving multiple victims with
Some of these drugs are subject to
being abused, e.g. orphenadrine, baclofen.