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72 Antidepressant (Tricyclic) Drug Toxicosis

PROGNOSIS & OUTCOME Prevention SUGGESTED READING
• Keep medications out of the reach of pets. Bloom FE: Neurotransmission and the central nervous
VetBooks.ir in most cases in 12-24 hours, up to 72 hours Technician Tips & Gilman’s the pharmacological basis of therapeu-
• Do not store human and veterinary medica-
• Prognosis is good in most cases (signs abate
system. In Brunton LL, et al, editors: Goodman
tions together.
for extended-release formulations).
tics, ed 11, New York, 2006, McGraw-Hill Profes-
sional, pp 317-340.
• Prognosis worsens if kidney injury or
hyperthermia occur. Closely monitor vital signs. AUTHOR & EDITOR: Tina Wismer, DVM, MS, DABVT,
DABT
Client Education
PEARLS & CONSIDERATIONS
Take pills over the sink so that if a pill is
Comments dropped, pets cannot ingest it from the floor.
Low doses of these medications cause depressive
signs that usually do not need medical interven-
tion. Higher doses cause stimulatory signs that
need to be treated.

Antidepressant (Tricyclic) Drug Toxicosis Client Education
Sheet

BASIC INFORMATION
PHYSICAL EXAM FINDINGS Differential Diagnosis
Definition • Initial findings include lethargy, vomiting, • Toxicology rule outs: amphetamines, methyl-
Tricyclic antidepressant (TCA) toxicosis is and ataxia. xanthines, pseudoephedrine, cocaine, herbal
caused by accidental ingestion or inadvertent • Later, any combination of disorientation, preparations containing ma huang or guarana
overdose of this class of drug, resulting in tremors, hyperactivity, coma, seizures root, quinidine, propranolol, albuterol, digoxin
gastrointestinal (GI), central nervous system • Hypotension, tachycardia or bradycardia, • Non-toxicology rule outs: hyperkalemia,
(CNS), and cardiovascular signs. In fatal cases, and other cardiac arrhythmias, mydriasis, cardiomyopathy, other primary cardiac
conduction disturbances (cardiovascular toxi- dyspnea, ileus, urinary retention, aci- diseases, epilepsy
cosis) are the main cause of death. dosis, hyperthermia, and dyspnea due
to pulmonary edema may occur. Body Initial Database
Synonyms temperature and respiratory rate should • Neurologic exam (p. 1136)
TCAs: amitriptyline (Elavil), amoxapine, clo- be recorded at presentation and monitored • Electrocardiogram (p. 1094) if tachycardia
mipramine (Clomicalm), desipramine, doxepin carefully. or arrhythmia on physical exam
(Adapin), imipramine (Tofranil), maprotiline, • Arterial blood pressure (p. 1065)
nortriptyline, protriptyline, trimipramine Etiology and Pathophysiology • Blood gas (acid-base status)
Source:
Epidemiology • TCAs are used in humans to treat a variety Advanced or Confirmatory Testing
SPECIES, AGE, SEX of disorders; used in dogs for pituitary- TCAs can be detected in serum, plasma, whole
All pets are at risk if they have access to these dependent hyperadrenocorticism, cognitive blood, and urine; assay not readily available
medications. Younger animals, and dogs > cats, dysfunction, aggression, fear/anxiety disor- and not useful for clinical cases. Contact a
are more likely to be exposed because of their ders, and obsessive-compulsive disorder; and diagnostic laboratory or a human hospital for
chewing or inquisitive natures. used in cats for urine spraying and anxiety additional information.
disorders.
RISK FACTORS Mechanism of toxicosis: TREATMENT
TCAs are commonly available prescription • TCAs inhibit sodium channels in the
medications in a household. Dogs are at myocardium, which slows ventricular Treatment Overview
increased risk for a large exposure because they depolarization. Their neurologic effects are • First stabilize the patient by managing any
tend to chew on the bottles/containers. Cats thought to be due to inhibition of the critical neurologic or cardiovascular effects.
may ingest a dropped tablet. reuptake of the neurotransmitters dopamine, Once stabilized, consider decontamination
norepinephrine, and serotonin in the CNS (emesis and activated charcoal).
Clinical Presentation and through blocking acetylcholine at the • Hospitalization may be required for > 24
DISEASE FORMS/SUBTYPES neuronal synapses. They also have antihis- hours for supportive care.
Mild signs (sedation, lethargy, vomiting) at low taminic, anticholinergic, and alpha-adrenergic
dosages and severe signs (tremors, hyperactivity, blocking effects. Acute General Treatment
cardiac arrhythmias, seizures) at high doses • Stabilization: initially, may include manag-
DIAGNOSIS ing seizures or severe hyperactivity with
HISTORY, CHIEF COMPLAINT diazepam, IV fluids for hypotension, and
• History of exposure or use of a TCA Diagnostic Overview managing significant cardiac arrhythmias.
• Lethargy, sedation, vomiting, and ataxia Diagnosis is facilitated with a history of use of Avoid atropine (use only preanesthetic
within 30 minutes to a few hours of acute a TCA in the household or known accidental dose 0.01-0.02 mg/kg IV if necessary)
exposure overdose together with GI, CNS, or cardio- for bradycardia because it may add to the
• Agitation, tremors, seizures, cardiac arrhyth- vascular effects within 30 minutes to several anticholinergic effects of TCAs. Oxygen
mias (usually indicate severe toxicosis) hours after the exposure. therapy for dyspneic patients.

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