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Combined H1 and H2 Antagonist Use in Acute Allergic Syndromes Results in Faster Improvement of Urticaria


  • In pediatric patients (ages 0-18) with acute allergic syndromes, does combined H1 and H2 antagonist use help expedite the improvement in symptoms?

Clinical Bottom Lines

  1. Combined H1 and H2 antagonist use in patients with acute allergic syndromes results in faster improvement of urticaria.
  2. H2 antagonist did not have a significant effect on angioedema, BP, or respiratory symptoms.
  3. No significant adverse effects were associated with H2 antagonist administration.

Summary of Key Evidence

  1. Randomized, double-blind control trial involving 91 adult patients ages 19-79 years.
  2. Study showed a significantly greater proportion of patients with resolved urticaria at 2 hrs in the Ranitidine group (91.7%) compared to the placebo group (73.8%, P=0.02, NNT=5).
  3. When treated earlier with ranitidine, there was a greater reduction in patients with urticaria at 2 hrs. (Duration <12hrs: 6%, Duration >12hrs: 20%).
  4. A greater number of patients in the placebo group required additional doses of antihistamines compared to the ranitidine group (23.3% and 4.2%, respectively).
  5. The proportion of patients without angioedema at 2 hrs did not differ between the ranitidine and placebo groups (77.1% and 67.4%, respectively).1
  6. No difference in either group was seen in the proportion of patients with urticaria at 2 hrs when Epinephrine was administered (OR no epi: 0.27, OR epi: 0.33).

Additional Comments

  • While the study showed that combined H1 and H2 antagonist use expedited the resolution of urticaria in adults, there are no studies conducted in the pediatric population.
  • The study did not look to see whether H2 antagonist use is beneficial in severe anaphylaxis.
  • No significant adverse effects were seen with treatment.
  • Cost:  Zantac OTC (30 tablets) costs about $11.


  1. Lin, et al. Improved Outcomes in Patients with Acute Allergic Syndromes Who Are Treated With Combined H1 and H2 Antagonists. Annals of Emergency Medicine 2000;36: 462-8.

CAT Author: Cheryl Tran, MD

CAT Appraisers: Francis McBee-Orzulak, MD

Date appraised: October 31, 2007

Last updated October 29, 2008
Department of Pediatrics and Communicable Diseases
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