April 8, 2002: What is the toxicity of muscle relaxants?

The group of drugs that are classified as muscle relaxants differ greatly in pharmacologic and toxicologic properties.  Most of the skeletal muscle relaxants depress the CNS.  Some of the drugs have anticholinergic (thus the hallucinations) and antihistaminic properties.  Presentation of a child that has ingested a muscle relaxant includes CNS and respiratory depression, muscle flaccidity, and possibly anticholinergic effects i.e.

  • Blind as a bat (dilated pupils)                                                          
  • Hot as a hare (warm)
  • Red as a Beet
  • Dry as a bone
  • Mad as a hatter (central anticholinergic-hallucination)       

Other frequent anticholinergic signs are tachycardia and decreased GI motility (no bowel sounds).

Treatment is supportive.  Serum concentrations are not available in hospital laboratories.  These drugs are not identified on urine drug screens.  Hallucinations and agitation can be managed with benzodiazepines.

 Next week, specific toxicities.

As always, if there are any questions, call the MTPC.

I am interested in any questions that you would like answered in “Question of the Week.”  Please e-mail me with any suggestions.


Donna Seger, M.D.

Medical Director

Middle Tennessee Poison Center