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Antihistamines/Cold Medications Toxicosis 73

• Decontamination of the patient (p. 1087) after serotonin syndrome (hyperthermia, agitation, PEARLS & CONSIDERATIONS
stabilization. For patients without clinical signs nervousness), especially if diazepam is not Comments
VetBooks.ir rhythm, and blood pressure should precede • Severely affected animals: monitor for an • Therapeutic dosages of various TCAs in Diseases and Disorders
effective.
on presentation, measurement of heart rate,
animals range between 1 and 4 mg/kg. Mild
decontamination. Consider emesis induction
additional 24 hours after cessation of signs
(apomorphine or 3% hydrogen peroxide in
seen at the recommended dosage and may
dogs, xylazine or dexmedetomidine in cats) if for the development of pulmonary edema, adverse effects (sedation, lethargy) can be
coagulation disorders, and pancreatitis.
the exposure occurred < 1 hour earlier. With not require any treatment.
large exposures, activated charcoal and/or Drug Interactions • Acute exposure of > 15-20 mg/kg can be
gastric lavage may be considered. Concurrent use of other sedatives, anticholin- potentially lethal.
• Multiple doses of activated charcoal (q 6-8h) ergics, antihistamines, sympathomimetics, or • Delayed gastric emptying (paralytic ileus)
may be indicated because of enterohepatic highly protein-bound drugs can interact with sometimes can prolong toxicity.
recirculation of TCAs. GI absorption of the the functioning of TCAs.
TCA may be prolonged because of anticho- Prevention
linergic activity (paralytic ileus). Possible Complications Clients should be instructed to keep all medica-
• Duration of treatment: initially monitor the Possible CNS damage from severe seizures or tions in a tightly secured place to prevent pets
patient for a minimum of 6 hours for CNS myocardial problems (i.e., congestive heart from chewing on the containers.
and cardiac effects if no signs were present failure) from cardiac tachyarrhythmias
at admission. If signs develop, treatment may Technician Tips
be necessary for 1-2 days or more. Recommended Monitoring Several TCAs are used off label in cats and
• Maintain cardiovascular function and ade- • CNS effects (seizures), heart rate, blood dogs. Clomicalm is an approved veterinary
quate blood pressure. pressure, electrocardiogram (cardiac arrhyth- product for separation anxiety in dogs.
• Manage vomiting with maropitant 1 mg/kg mias), GI motility (ileus), acid-base status
SQ q 24h or metoclopramide 0.2-0.5 mg/ (acidosis), respirations +/− thoracic radio- Client Education
kg PO, SQ, or IM q 6-8h. graphs (pulmonary edema) Discuss adverse effects with the owner when
• Monitor for acidosis. Increased blood pH • Although there are no direct blood or organ prescribing TCAs for pets.
has improved prognosis in dogs experimen- effects, monitor CBC and serum biochem-
tally poisoned by TCAs. Correct acidosis istry profile in severely affected animals. SUGGESTED READING
with sodium bicarbonate. Acid-base monitor- Secondary conditions such as disseminated Volmer PA: Tricyclic antidepressants. In Peterson
ing is ideal (in the absence of monitoring, intravascular coagulation, pancreatitis, and ME, et al, editors: Small animal toxicology, ed 3,
can give sodium bicarbonate at a dose of renal effects secondary to rhabdomyolysis St. Louis, 2013, Saunders, pp 328-330.
2-3 mEq/kg IV slowly over 15-30 minutes). from severe tremors can occur.
• Supportive care: fluid diuresis with IV fluids AUTHOR: Camille DeClementi, VMD, DABT, DABVT
EDITOR: Tina Wismer, DVM, MS, DABVT, DABT
• Thermoregulation: maintain body tempera- PROGNOSIS & OUTCOME
ture within normal range
• Diazepam (0.2-0.5 mg/kg IV) can be used TCAs have a narrow margin of safety. Good
to treat agitation. prognosis if treated early and intensively. Poor
• Cyproheptadine (dogs: 1.1 mg/kg PO or per prognosis if severe cardiac arrhythmias or
rectum; cats: 2-4 mg total) can be used for seizures develop.

Antihistamines/Cold Medications Toxicosis Client Education
Sheet

BASIC INFORMATION ○ Nonsedating because they do not cross winter, and toxicosis from antihistamines may
the blood-brain barrier at therapeutic doses be more frequent in spring.
Definition
Toxicosis in pets caused by accidental acute Epidemiology Clinical Presentation
ingestion or overdose of human cold medica- SPECIES, AGE, SEX HISTORY, CHIEF COMPLAINT
tions (CMs) containing (depending on the All dogs and cats susceptible History or evidence of exposure:
purpose) antihistamines, decongestants, anal- • Antihistamines: lethargy, sedation, mydriasis
gesics, cough suppressants, or expectorants RISK FACTORS within a few hours, or agitation, hyperactiv-
• Availability of the medications in the pet’s ity, vocalization, seizures (rare), nervousness
environment or accidental overdose given (paradoxical reaction), vomiting, diarrhea
Synonyms by the owner • Dextromethorphan: sedation or agitation,
• First-generation antihistamines: chlorpheni- • Pre-existing liver disease may prolong ataxia, panting, facial edema
ramine, dimenhydrinate, diphenhydramine, elimination and therefore duration of clinical
promethazine, meclizine, hydroxyzine signs. PHYSICAL EXAM FINDINGS
○ Sedating because they can cross the blood- • Antihistamines: central nervous system
brain barrier GEOGRAPHY AND SEASONALITY (CNS) depression, anticholinergic effects (dry
• Second-generation antihistamines: loratadine, Seasonal human use of these drugs makes mouth, tachycardia, mydriasis, hyperthermia,
cetirizine, fexofenadine toxicosis from CMs more likely during the hypertension or hypotension, seizures,

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