Due to the increased likelihood of allergic
reactions in atopic patients, it is important that a complete history
of known and suspected allergies as well as allergic-like symptoms,
e.g., rhinitis, bron-chial asthma, eczema and urticaria, must be obtained
prior to any medical procedure utilizing these products. A mild allergic
reaction would most likely include generalized pruritus, erythema
or urticaria (approximately 1 in 250,000). Such reactions will generally
respond to an antihistamine such as 50 mg of diphenhydramine or its
equivalent. In the rarer, more serious reactions (approximately 1
in 1,000,000) laryngeal edema, bronchospasm or hypotension could develop.
Severe reactions which may require emergency measures are often characterized
by peripheral vasodilation, hypotension, reflex tachycardia, dyspnea,
agitation, confusion and cyanosis progressing to unconsciousness.
Treatment should be initiated immediately with 0.3 to 0.5 mL of 1:1000
epinephrine subcutaneously. If bronchospasm predominates, 0.25 to
0.50 grams of intravenous aminophylline should be given slowly. Appropriate
vasopressors might be required. Adrenocorticosteroids, even if given
intravenously, exert no significant effect on the acute allergic reactions
for a few hours. The administration of these agents should not be
regarded as emergency measures for the treatment of allergic reactions.
Apprehensive patients may develop
weakness, pallor, tinnitus, diaphoresis and bradycardia following
the administration of any diagnostic agent. Such reactions are usually
non-allergic in nature and are best treated by having the patient
lie flat for an additional 10 to 30 minutes under observation.