Drug General Information (ID: DDI7XH8MOB)
  Drug Name Diphenhydramine Drug Info Bretylium Drug Info
  Drug Type Small molecule Small molecule
  Therapeutic Class Antiallergic Agents Antiarrhythmic Agents
  Structure

 Mechanism of Diphenhydramine-Bretylium Interaction (Severity Level: Moderate)
     Increased risk of prolong QT interval Click to Show/Hide Mechanism Graph
Could Not Find 2D Structure
      Drug Name Diphenhydramine Bretylium
      Mechanism Prolong QT interval Prolong QT interval
      Key Mechanism Factor 1
Factor Name QT interval
Factor Description Long QT syndrome is a heart signaling disorder that can cause a fast, chaotic heartbeat (arrhythmia). Many people may not exhibit symptoms, and usually the condition is detected during routine medical tests. In others, the most common symptoms include: sudden fainting, palpitations, dizziness, seizures, sudden death.
      Mechanism Description
  • Increased risk of prolong QT interval by the combination of Diphenhydramine and Bretylium 

Recommended Action
      Management Australian authorities recommend avoiding concomitant use of diphenhydramine and class Ia or class III antiarrhythmic agents. Additionally, patients should be counseled to not exceed the recommended dosage and frequency or duration of use of diphenhydramine, and to seek prompt medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope.

References
1 Cerner Multum, Inc. "Australian Product Information.".
2 Husain Z, Hussain K, Nair R, Steinman R "Diphenhydramine induced QT prolongation and torsade de pointes: An uncommon effect of a common drug." Cardiology 17 (2010): 509-11. [PMID: 20865683]
3 Poluzzi E, Raschi E, Godman B, et.al "Pro-arrhythmic potential of oral antihistamines (H1): Combining adverse event reports with drug utilization data across Europe." PLoS One 10 (2014): epub. [PMID: 25785934]
4 Shah A, Yousuf T, Ziffra J, Zaidi A, Raghuvir R "Diphenhydramine and QT prolongation - A rare cardiac side effect of a drug used in common practice." J Cardiol Cases 12 (2015): 126-9. [PMID: 30546575]