eMedicine Specialties > Emergency Medicine > Toxicology

Toxicity, Antihistamine: Follow-up

Author: L Keith French, MD, Chief Resident, Department of Emergency Medicine, Oregon Health and Sciences University
Coauthor(s): Nathanael J McKeown, DO, Assistant Professor, Oregon Health and Science University; Medical Toxicologist, Oregon Poison Center; Attending Physician, Emergency Medicine, Portland Veteran Affairs Medical Center, Oregon Health and Science University
Contributor Information and Disclosures

Updated: Jun 10, 2009

Follow-up

Further Inpatient Care

  • Rhabdomyolysis
    • Treat with aggressive fluid support to maintain urine output at 2 mg/kg/h.
    • Consider using sodium bicarbonate to alkalinize the urine.
    • Consult a nephrologist for oliguria or renal failure, and arrange hemodialysis for the anuric or severely acidotic patient.
  • Treat acute dystonic reactions with benzodiazepines.
  • Multiple doses of activated charcoal are not recommended because charcoal concretions may form leading to intestinal obstruction or ileus. Antihistamines may induce intestinal ileus causing delayed absorption of drug and delayed toxicity.
  • Perform cardiac monitoring on all symptomatic patients or as long as tachycardia, conduction delays, or prolonged QT intervals persist.

Transfer

  • If intensive care units or telemetry is unavailable, benefits of transfer may outweigh benefits of keeping the patient.

Deterrence/Prevention

  • Childproof safety caps and clear labeling have been shown to decrease toxic exposures in young children and elderly individuals.
  • Anticholinergics should not be use as sleep aids in elderly persons.

Complications

  • Multisystem organ failure and death have resulted from severe antihistamine overdose.

Prognosis

  • Among first-generation antihistamines, mortality from diphenhydramine occurs more than any other agent.
  • In the United States, diphenhydramine is used more commonly than other antihistamines. It also is associated with more cardiotoxicity and a higher incidence of seizures than other first-generation antihistamines.
  • Pheniramine, an antihistamine commonly used in Australia, also is associated with a relatively high incidence of seizures.
  • Among nonsedating piperidine antihistamines, terfenadine has been implicated more often than astemizole, loratadine, or fexofenadine in the formation of prolonged QT syndrome and torsade de pointes.
  • The prognosis is affected by the presence of underlying medical conditions, co-ingestions, and the amount of drug ingested.
  • The vast majority of patients recover with supportive care and observation.

Patient Education

Miscellaneous

Medicolegal Pitfalls

  • Failure to recognize the anticholinergic syndrome
  • Failure to control severe agitation and seizures in a patient with severe delirium and uncontrolled muscular activity
  • Reliance on a toxicology screen instead of clinical presentation to make the diagnosis of antihistamine poisoning
  • Failure to diagnosis and treat associated acetaminophen poisoning
  • Failure to provide adequate cardiac monitoring for patients with persistent QRS or QT interval prolongation
  • Casual administration of physostigmine to patients with contraindications to its use (eg, co-ingestion of cyclic antidepressants, cardiac conduction delays, or unknown ingestion)
  • Failure to rapidly control severe hyperthermia in patients with paralysis and aggressively perform cooling measures
  • Failure to monitor paralyzed patients with continuous EEG for evidence of ongoing seizure activity
 
Acknowledgments

The authors and editors of eMedicine gratefully acknowledge the contributions of previous authors, David J McCann, MD, and Brett Roth, MD, to the development and writing of this article.



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References
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Further Reading

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Keywords

antihistamine toxicity, antihistamine overdose, alkylamine, antihistamine exposure, antihistamine poisoning, brompheniramine, cetirizine, clemastine, cyproheptadine, desloratadine, diphenhydramine, doxylamine, ethanolamine, ethylenediamine, fexofenadine, H1-receptor antagonists, H2-receptor antagonists, levocetirizine, loratadine, meclizine, nonsedating H1 blockers, phenothiazine, piperazine, promethazine, tripelennamine, triprolidine

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Contributor Information and Disclosures

Author

L Keith French, MD, Chief Resident, Department of Emergency Medicine, Oregon Health and Sciences University
Disclosure: Nothing to disclose.

Coauthor(s)

Nathanael J McKeown, DO, Assistant Professor, Oregon Health and Science University; Medical Toxicologist, Oregon Poison Center; Attending Physician, Emergency Medicine, Portland Veteran Affairs Medical Center, Oregon Health and Science University
Nathanael J McKeown, DO is a member of the following medical societies: American Academy of Clinical Toxicology, American College of Emergency Physicians, American College of Medical Toxicology, Society for Academic Emergency Medicine, and Wilderness Medical Society
Disclosure: Nothing to disclose.

Medical Editor

David C Lee, MD, Research Director, Department of Emergency Medicine, Associate Professor, North Shore University Hospital and New York University Medical School
David C Lee, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Medical Toxicology, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

John T VanDeVoort, PharmD, Regional Director of Pharmacy, Sacred Heart & St. Joseph's Hospitals
John T VanDeVoort, PharmD is a member of the following medical societies: American Society of Health-System Pharmacists
Disclosure: Nothing to disclose.

Managing Editor

Michael J Burns, MD, Instructor, Department of Emergency Medicine, Harvard University Medical School, Beth Israel Deaconess Medical Center
Michael J Burns, MD is a member of the following medical societies: American Academy of Clinical Toxicology, American College of Emergency Physicians, American College of Medical Toxicology, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

Asim Tarabar, MD, Assistant Professor, Director, Medical Toxicology, Department of Emergency Medicine, Yale University School of Medicine; Consulting Staff, Department of Emergency Medicine, Yale-New Haven Hospital
Disclosure: Nothing to disclose.

 
 
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