Can Avil (diphenhydramine) and Dexamethasone be given before blood transfusion to prevent allergic reactions?

Premedication Before Blood Transfusion to Prevent Reactions

Current guidelines do not recommend routine use of diphenhydramine (Avil) and dexamethasone before blood transfusion to prevent allergic reactions. 1

Current Evidence-Based Recommendations

The most recent guidelines from the Association of Anaesthetists (2025) specifically advise against indiscriminate use of steroids and/or antihistamines for transfusion reaction prevention 1. Instead, a personalized approach based on individual risk factors is recommended.

Why Routine Premedication Is Not Recommended:

1. Lack of Efficacy Evidence:

   • Multiple studies have failed to demonstrate that premedication prevents transfusion reactions 2, 3, 4
   • One study found that premedication with diphenhydramine was actually associated with a non-significant increase in allergic reactions (odds ratio 1.74) 2

2. Potential Adverse Effects:

   • Diphenhydramine can cause sedation, hypotension, and tachycardia
   • Repeated doses of steroids may further suppress immunity in immunocompromised patients 1

Appropriate Approach to Transfusion Reaction Prevention

Risk Assessment-Based Approach:

1. Identify high-risk patients:

   • History of multiple previous transfusion reactions
   • Multiple drug allergies
   • History of severe allergic reactions
   • Asthma

2. For standard risk patients:

   • No premedication
   • Proper monitoring during transfusion (pulse, blood pressure, temperature, respiratory rate)
   • Observations should be completed before transfusion, 15 minutes after start, and within 60 minutes of completion 1

3. For high-risk patients only:

   • Consider targeted premedication based on specific risk factors
   • For those with history of allergic reactions: antihistamine alone may be appropriate
   • For those with history of febrile reactions: antipyretics alone may be sufficient

Management of Reactions When They Occur

If a transfusion reaction does occur, the approach should be symptom-directed:

1. For febrile reactions:

   • Stop or slow the infusion
   • Administer intravenous paracetamol/acetaminophen 1

2. For allergic reactions:

   • Stop or slow the infusion
   • Administer antihistamine 1

3. For severe reactions/anaphylaxis:

   • Stop the infusion immediately
   • Follow local anaphylaxis protocols
   • Diphenhydramine is indicated for management of acute allergic reactions to blood or plasma 5

Common Pitfalls to Avoid

1. Overuse of premedication:

   • Creates false sense of security
   • Exposes patients to unnecessary medication side effects
   • May mask early signs of serious reactions

2. Failure to monitor properly:

   • Respiratory rate monitoring is essential as dyspnea and tachypnea are typical early symptoms of serious transfusion reactions 1

3. Confusing prevention with treatment:

   • While diphenhydramine is not recommended for routine prevention, it is appropriate for treatment of allergic reactions when they occur 5

Bottom Line

Focus on proper monitoring during transfusion rather than routine premedication. Reserve diphenhydramine and dexamethasone for treatment of reactions when they occur or for carefully selected high-risk patients based on their specific history.