Anaphylaxis: combining ranitidine and diphenhydramine was not clearly better than diphenhydramine alone

Clinical bottom line (level 1b-)

  1. Patients with acute allergic syndromes who take ranitidine and diphenhydramine compared with diphenydramine alone were not clearly more likely to have a reduction in symptoms at 2 hours.
Lin et al: Annals of Emergency Medicine 2000; 36: 462-468
Expires November 2004

The study

Double-blinded concealed randomised trial without intention-to-treat
Setting: emergency department, 2 acute hospitals, USA

91 patients (aged 20 to 79 (median 32), 60% female) with acute allergic syndromes - acute urticaria, acute angioedema, acute unexplained stridor or acute pruritic rash, after an ingested foor or ingested, inhaled or injected drug or after contact with latex.

Excluded if
  • aged < 18
  • manifestations present > 12 hours
  • pregnant


    • Note:
  • Patients could receive steroids, epinephrine, bronchodilators and additional doses of antihistamine if required.


    • Control Group: (n = 43, 43 analysed): diphenhydramine 50 mg iv and saline iv
    Experimental Group: (n = 48, 48 analysed): diphenhydramine 50 mg iv and ranitidine 50 mg iv

    100% followed for 2 hours

    The evidence

    Outcome Time to outcome CEREERRRR
    (95% CI)    		ARR
    (95% CI)    		NNT
    (95% CI)
    presence of angioedema or urticaria 2 hours 14
    (32.6%)    		 23
    (47.9%)    		 -47%
    (-148% to 13%)    		 -15.4%
    (-35.3% to 4.54%)    		 -7
    (NNT = 22 to infinity;
    NNH = 3 to infinity)
    presence of wheezing 2 hours 0
    (0.00%)    		 1
    (2.08%)    		 %
    (% to %)    		 -2.08%
    (-6.12% to 1.96%)    		 -48
    (NNT = 51 to infinity;
    NNH = 16 to infinity)

    Citation

    1. Lin RY, Pesola GR, Knight RJ, et al: improved outcomes in patients with acute allergic syndromes who are treated with combined H1 and H2 antihistamines in acute allergic syndromes. Annals of Emergency Medicine 2000; 36: 462-468
    Search Terms: from other articles noted in Best Evidence
    Contributor: Chris Ball, November 2001
    Reviewer:

    Clinical Question.
    Patient acute allergic syndrome - urticaria, angioedema
    Intervention or Exposure ranitidine and diphenhydramine
    Comparison diphenhydramine
    Outcome reduction in clinical signs