H2 Blockers in Allergic Reactions

1. H2 Blockers in Allergic Reactions Maureen Chase

2. The Study • Improved Outcomes in Patients with Acute Allergic Syndromes who are Treated with combined H1 and H2 Antagonists • Lin, et al, Annals of Emergency Medicine Nov 2000

3. Study Design • Randomized double blind placebo controlled study of 91 patients with acute allergic syndromes in an urban academic center ER • Control Group- 50 mg IV benadryl and saline solution • Study group- 50 mg IV benadryl and 50 mg Ranitidine

4. Patient Sample • Adults > 18 yo • Acute angioedema, acute unexplained stridor and acute pruritic rash • Symptoms present < 12 hrs from time of exposure to presumed allergen ( ingested food, inhaled or injected drug or contact with latex)

5. Endpoint • Resolution Urticaria, angioedema and erythema at 2 hours

6. Resolution of Symptoms at 2 hours

7. Study conclusions • Significant difference between study and control group of resolution of urticaria alone and urticaria with angioedema • NO difference between groups w/r/t angioedema alone or erythema in presence or absence of urticaria

8. Study Flaws

9. Study Flaws, cont. • No Ranitidine + saline group

10. Background • Histamine anatgonists in the treatment of acute allergic reactions • Runge, et al, Annals of Emer Med Mar 1992 • visual analog scale assessment of allergic symptoms in 35 patients at presentation and 30’ after treatment with cimetidine and diphemhydramine, alone or in combination

11. Urticaria resolution

12. Runge, et al, cont. • H1 and H2 blockers combined are more effective than H1 blockers alone in the treatment of urticaria ( p = 0.027) • FLAW- small sample size

13. HUPisms • Studies suggest possible benefit of H2 blockers in treatment of some aspects of allergic response ( urticaria) • Current data DO NOT support use of H2 blockers in treatment of all acute allergic reactions • ** Seems reasonable but no clear benefit**