Diphenhydramine as Adjuvant Therapy for Acute Migraine: An Emergency Department–Based Randomized Clinical Trial

Study objective More than 1 million patients present to US emergency departments (EDs) annually seeking care for acute migraine. Parenteral antihistamines have long been used in combination with antidopaminergics such as metoclopramide to treat acute migraine in the ED. High-quality data supporting this practice do not exist. We determine whether administration of diphenhydramine 50 mg intravenously+metoclopramide 10 mg intravenously results in greater rates of sustained headache relief than placebo+metoclopramide 10 mg intravenously. Methods This was a randomized, double-blind, clinical trial comparing 2 active treatments for acute migraine in an ED. Eligible patients were adults younger than 65 years presenting with an acute moderate or severe headache meeting International Classification of Headache Disorders-2 migraine criteria. Patients were stratified according to presence or absence of allergic symptoms. The primary outcome was sustained headache relief, defined as achieving a headache level of mild or none within 2 hours of medication administration and maintaining this level of relief without use of any additional headache medication for 48 hours. Secondary efficacy outcomes included mean improvement on a 0 to 10 verbal scale between baseline and 1 hour, the frequency with which subjects indicated they would want the same medication the next time they present to the ED with migraine, and the ED throughput time. Sample size calculation using a 2-sided α of .05, a β of .20, and a 15% difference between study arms determined the need for 374 patients. An interim analysis was conducted when data were available for 200 subjects. Results Four hundred twenty patients were approached for participation. Two hundred eight eligible patients consented to participate and were randomized. At the planned interim analysis, the data and safety monitoring board recommended that the study be halted for futility. Baseline characteristics were comparable between the groups. Fourteen percent (29/208) of the sample reported allergic symptoms. Of patients randomized to diphenhydramine, 40% (40/100) reported sustained relief at 48 hours, as did 37% (38/103) of patients randomized to placebo (95% confidence interval [CI] for difference of 3%: -10% to 16%). One hour after medication administration, patients randomized to diphenhydramine improved by a mean of 5.1 on the 0 to 10 scale versus 4.8 for those randomized to placebo (95% CI for difference of 0.3: -0.6 to 1.1). Eighty-five percent (84/99) of the patients in the diphenhydramine arm reported they would want the same medication combination during a subsequent ED visit, as did 76% (77/102) of those who received placebo (95% CI for difference of 9%: -2% to 20%). Median ED length of stay was 122 minutes (interquartile range 84 to 180 minutes) in the diphenhydramine group and 139 minutes (interquartile range 90 to 235 minutes) in the placebo arm. Rates of adverse effects, including akathisia, were comparable between the groups. Conclusion Intravenous diphenhydramine, when administered as adjuvant therapy with metoclopramide, does not improve migraine outcomes.