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108 Baclofen and Other Centrally Acting Muscle Relaxants Toxicosis

• Acute back pain with neurologic deficits may • Exercise caution with examination if back SUGGESTED READING
represent a surgical emergency and should pain may be associated with spinal instability, Lorenz MD, et al: Handbook of veterinary neurology,
VetBooks.ir • Perceived back pain may actually be abdomi- Client Education AUTHOR: Peter Moak, DVM
such as fracture or luxation.
be evaluated immediately.
St. Louis, 2012, Saunders, pp 413-431.
nal or kidney pain; use care when isolating
EDITOR: Leah A. Cohn, DVM, PhD, DACVIM
• Owner should monitor for recurrence of
source of pain on examination.
signs.
Technician Tips • Acute worsening of signs warrants emergency
• Avoid injury. Examination of painful patients evaluation and treatment.
may require analgesia and restraint, although
opioids can alter exam findings.

Baclofen and Other Centrally Acting Muscle Relaxants Toxicosis Client Education
Sheet

BASIC INFORMATION Drugs Chief Complaints
Definition Baclofen Onset of signs within 15 minutes to 7 hours after ingestion
Syndrome developing after the ingestion of one Dogs: vomiting, ataxia, hypersalivation, depression, vocalization,
of several centrally acting skeletal muscle relax- disorientation or agitation, recumbency, coma, seizure
ants (SMRs) and characterized mainly by central Cats: vomiting, depression, ataxia, weakness, hypothermia,
nervous system (CNS) depression recumbency, coma, mydriasis, diarrhea
Cyclobenzaprine Onset within 30 minutes to several hours
Synonyms Depression, ataxia, vomiting, weakness, mydriasis, tachycardia,
vocalization, agitation, tremors, seizures
Generic Name Trade Names
Orphenadrine Onset within 30 minutes to several hours
Baclofen Lioresal, Kemstro Weakness, vomiting, tachycardia, agitation, seizures
Carisoprodol Soma Tizanidine Onset within 30 minutes to 4 hours
Lethargy, somnolence, bradycardia, hypotension, recumbency,
Chlorphenesin carbamate Maolate weakness, vocalization, urinary retention, collapse, coma
Chlorzoxazone Parafon Forte Other SMRs: carisoprodol, chlorphenesin Stupor, hypotension, coma, respiratory depression, seizures (rare)
Cyclobenzaprine Flexeril carbamate, chlorzoxazone,
metaxalone, methocarbamol,
Guaifenesin Gecolate
guaifenesin
Metaxalone Skelaxin

Methocarbamol Robaxin,
Robaxin-V
Orphenadrine Norflex
Tizanidine Zanaflex
PHYSICAL EXAM FINDINGS • Pale mucous membranes, prolonged capillary

Baclofen refill time
• As above (see Table) • Hypothermia
• Hypothermia (if recumbent), hyperthermia Other SMRs
Epidemiology (if seizing) • Depression, somnolence, weakness
SPECIES, AGE, SEX • Hypertension or hypotension • Hypoventilation, cyanosis
All species susceptible; dogs more likely because • Tachycardia or bradycardia • Tachycardia, hypotension
of indiscriminate eating habits • Hypoventilation • Hypothermia (if recumbent), hyperthermia
• Miosis (dogs) or mydriasis (cats) (if seizing)
RISK FACTORS • Muscular hypotonia, weakness
• Availability of muscle relaxants in the animal’s Cyclobenzaprine and orphenadrine Etiology and Pathophysiology
environment • Depression or agitation, hyperesthesia (cats), Source:
• Many people taking skeletal muscle relax- vocalization • Most centrally acting SMRs are used for
ants for spasticity disorders (e.g., multiple • Miosis (dogs) or mydriasis (cats), nystagmus controlling spasticity in humans with neu-
sclerosis) also take other medications, increas- (occasional, dog and cat) romuscular disorders. May also be prescribed
ing the risk for multiple drug exposures • Muscle weakness, tremors, fasciculation for relief of musculoskeletal pain.
by pets. • Panting Mechanism of toxicosis:
• Tachycardia or bradycardia • Baclofen: mimics gamma-aminobutyric
Clinical Presentation • Hyperthermia acid (GABA) in the spinal cord, blocking
HISTORY, CHIEF COMPLAINT Tizanidine excitatory responses to sensory input and
History of exposure to muscle relaxants or • Depression, weakness, ataxia causing flaccid paralysis. Seizures may be
presence of drugs in environment (see Table) • Hypotension, bradycardia due to interference with GABA release from

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