Figure 6 . Toxic epidermal necrolysis . |
AfroBrazilian / CC BY-SA 3.0 / bit . ly / 3WqCopZ |
Figure 7 . Toxic epidermal necrolysis . |
Jay2Base / CC BY-SA 4.0 / bit . ly / 42UMK3T |
Box 4 . COX-mediated hypersensitivity |
Box 5 . Recommendation for premedication for patients with previous reactions to contrast |
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This is characterised by respiratory and cutaneous manifestations and can be classified as :
• NSAID-exacerbated respiratory disease ( often , but not exclusively , in patients with comorbid asthma or rhinosinusitis ).
• NSAID-exacerbated urticaria and angioedema ( in patients with chronic spontaneous urticaria ).
• NSAID-induced cutaneous disease ( in otherwise asymptomatic patients ).
Source : Khan DA et al 2022 18
the index LA ; if allergy is confirmed
, they then assess alternatives typically held in dental or general practices in the local area to establish safety for clinically relevant LAs .
RADIOCONTRAST
REACTIONS can occur to iodinated contrast , used for CT and angiography , and gadolinium-based contrast , used for MRI . There is no cross-reactivity between iodinated IV contrast agents and gadolinium-based agents . There is also no cross-reactivity between iodinated IV contrast agents and shellfish . Iodinated radiocontrast agents vary in their osmolality , with iso-molar agents ( such as iodixanol ) associated with a very low rate of reactions . Other commonly used contrast agents ( for example , iohexol , iopamidol , ioversol , iopromide ) are low-osmolar . The rate of acute adverse reactions from non-ionic low- or iso-osmolar iodinated contrast is about 0.15-0.7 %, with a fatality rate for iodinated contrast at 2-9 per one million administrations of iodinated IV contrast agents , which is significantly better than the previously used ionic high-osmolar contrast agents . 90 The rate of reactions to gadolinium based contrast are 10-fold lower , estimated between 0.02-0.09 % percent , with more than 96 % mild and self-limiting reactions . 90
Reactions to contrast are predominantly Type 1 mediated or mild to moderate Type 4 reactions ( see table 1 ). Transient physiological reactions may occur , and it is sometimes difficult to distinguish theses from allergic reactions . Mild physiological reactions are transient and may manifest as warmth ( flushing ) or chills and nausea or vomiting , and can be managed with patient reassurance . Moderate to severe physiological reactions such as hypo- or
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• Non-urgent imaging — Adult : oral prednisolone 50mg at 13 , seven and one hour before contrast administration . and — Non-drowsy antihistamine ( 10mg loratadine or cetirizine or 180mg fexofenadine ) at 12 and 1 hour prior to contrast administration .
• Urgent imaging — Adult : hydrocortisone 200mg IV at 4-5 hours ( if possible *) and one hour before contrast administration . and — Non-drowsy oral antihistamine ( 10mg loratadine or cetirizine or
180mg of fexofenadine ) one hour before contrast administration .
* There is no evidence showing that premedication protocols of less than 4-5 hours are effective . Based on current practice and expert opinion of authors
hypertension or cardiac symptoms are rare and should be managed accordingly .
Although most reactions to contrast are mild and self-limiting , suspected allergic reactions warrant investigation , especially if further imaging is indicated for optimal medical care .
Specialist drug allergy clinics can provide skin testing ( PT , SPT , IDT ), advice and , sometimes , challenges . Testing is best performed 2-6 months after the reaction to allow for sufficient sensitivity and specificity of the skin tests . The aim of these investigations is to find a safe and suitable alternative agent . In the absence of the availability of timely skin testing , consider premedication and the use of an alternative agent with low or ideally iso-molality . Re-exposure to potentially cross-reactive contrast agents without specialist assessment and skin testing in patients who experienced a severe Type 4 reaction is contraindicated .
A
B
Premedication in patients with previous reactions is recommended , even if an alternative agent has been identified ( see box 5 ).
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CASE STUDIES
Case study one
JAMES , a 57-year-old Caucasian male
is referred for the assessment of a drug-related allergic reaction . He has a medical history of hypertension and gastroesophageal reflux disease . He has an atopic background with seasonal allergic rhinitis , atopic dermatitis and a self-reported allergy to penicillins ; he reports that he developed an isolated rash at age six years and has avoided beta-lactams since . On 22 June he develops severe abdominal pain and constipation . He is seen in ED and , following CT scan with iohexol contrast , is diagnosed with non-complicated diverticulosis . His baseline eosinophils , liver and creatinine function are normal . Considering the low risk reported
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Figure 8 . Patch testing .
Esid1997 / CC BY-SA 4.0 / bit . ly / 3q0mmaq
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Figure 9 . A hypersensitivity reaction on the hands from the use of topical anaesthesia . |
Figure 10 . Drug timeline .
Jan Polák / CC BY-SA 3.0 / bit . ly / 41VoDRy
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