Anaphylaxis: histamine-antagonists helped relieve pruritus.

Clinical bottom line (level 1b)

  1. Patients with acute allergic reaction who took diphenhydramine compared with cimetidine were more likely to have relief of pruritus (NNT = 3 at 30 minutes) .
  2. There was no clear benefit from adding cimetidine to diphenhydramine.
Runge et al: Annals of Emergency Medicine 1992; 21 (3): 237-242
Expires November 2004

The study

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

39 patients (aged mean 32 years, 62% male) with an acute allergic reaction and pruritus
Control Group: (n = 12, 10 analysed): cimetidine 300 mg iv and placebo
Experimental Group: (n = 14, 12 analysed): diphenhydramine 50 mg iv and placebo
Experimental Group: (n = 13, 13 analysed): diphenhydramine 50 mg iv and cimetidine 300 mg iv

90% followed for 30 minutes

The evidence

diphenhydramine v. cimetidine
Outcome Time to outcome CEREERRRR
(95% CI)		ARR
(95% CI)		NNT
(95% CI)
no relief from pruritus 30 minutes 4
(40.0%)		 0
(0.0%)		 100%
(% to %)		 40.0%
(9.64% to 70.4%)		 3
(1 to 10)

diphenhydramine and cimetidine v. cimetidine
Outcome Time to outcome CEREERRRR
(95% CI)		ARR
(95% CI)		NNT
(95% CI)
relief from pruritis 30 minutes 4
(40.0%)		 1
(7.69%)		 81%
(-46% to 97%)		 32.3%
(-1.33% to 66.0%)		 3
(NNT = 2 to infinity;
NNH = 75 to infinity)

Comments

  1. The small numbers and short follow-up make these results far less certain. The study was too small to show any difference between the diphenhydramine and the combination.

Citation

  1. Runge RW, Martinez JC, Caravati EM, et al: histamine antagonists in the treatment of acute allergic reactions. Annals of Emergency Medicine 1992; 21 (3): 237-242
Contributor: Chris Ball and Clare Wotton, November 1999
Reviewer:

Clinical Question.
Patient acute allergic reaction
Intervention or Exposure histamine antagonist
Outcome relief of pruritus