Some patients may develop urticaria and other allergic symptoms following blood product transfusion. Diphenhydramine (Benadryl, other brand names) is often given both to alleviate these symptoms and to prevent their occurrence. While relatively innocuous in most patients, diphenhydramine may be associated with significant side effects, especially in the elderly.


Background: In some health care facilities diphenhydramine is routinely administered prophylactically to all patients receiving blood products, even in the absence of known allergic reactions.


Effects diphenhydramine may have in the elderly (patients >= 70 years of age):

(1) delirium or disorientiation

(2) agitation

(3) altered consciousness or inattention

(4) urinary retention (and other anti-cholinergic effects)

(5) increased period of hospitalization


Indications for use of diphenhydramine:

(1) active treatment of current allergic reaction with urticaria and/or pruritis

(2) prophylaxis in a multiply transfused patient with a well-documented propensity for developing urticaria and/or pruritis following blood product transfusion.


Nonindications for use of diphenhydramine:

(1) prophylaxis in a patient without a definite history of allergic reactions to blood product administration, especially if the patient is elderly


Relative contraindications for the use of diphenhydramine:

(1) obstructive urinary symptoms

(2) history of significant adverse reaction to diphenhydramine

(3) current delirium, disorientation, agitation or other active psychiatric condition


To read more or access our algorithms and calculators, please log in or register.