Cutaneous drug eruptions

Question 1

Immunological vs non-immunological reactions

Answer 1

immune- true allergy
non- drug toxicity

Question 2

Explain immediate reactions

Answer 2

Occurs less than 1 hr after the last administered dose
Mediated by IgE antibodies
Symptoms = urticaria (raised itchy rash) or angiodema (swelling) leading to anaphylaxis

Question 3

Explain delayed reactions

Answer 3

Occurs after 1hr but normally 6hrs after last dose
Occasionally occurs weeks to months after start of medication
Mediated by IgG antibodies, immune complex, or T cells
Exanthematous eruption (papules)
Fixed or systemic reactions
Vasculitis

Question 4

Risk factors for drug eruptions

Answer 4

Female
Prior history of drug reaction
Recurrent drug exposure
HLA type
Certain disease states

Question 5

Classify exanthematous drug eruptions

Answer 5

Maculopapular or morbilliform
Most common
Occurs within 7-10 days after starting drug, but may occur faster if it is re-exposure
Start on trunk and spread to limbs and neck - bilateral and symmetrical
Accompanied by itch and mild fever
Adult - from medication
Child - viral cause
Antibiotics main culprit
Resolve in a few days to a week after stopping
Surface skin may peel off

Question 6

Classify fixed drug eruptions

Answer 6

ADR appearing in same site with re-exposure to drug
Occurs up to 2 weeks after first exposure and faster after next exposure
Well-defined round or oval patch of redness and swelling, sometimes may blister.
Paracetamol, NSAIDs, tetracycline, sulfonamides, salicylates, metronidazole, hyoscine butyl bromide, yellow food colouring.
Lesions resolve days-weeks after stopping
Unbroken lesions treat with potent topical steroid
Broken lesions protect with dressing until healed
Lesions can be painful

Question 7

Explain photosensitivity

Answer 7

Photo-toxic (sunburn redness)
or photo-allergic (allergic contact dermatitis like)
Generally prominent on sun-exposed sites (face, hands, V of the neck)
May or may not be itchy rash
Drugs known as photosensitisers
NSAIDs, antibiotics, diuretics, retinoids, sulfonylureas, antipsychotics, etc.
Can be used clinically (prior to therapy of skin cancer)

Question 8

Explain Toxic Epidermal Necrolysis and Stevens-Johnson syndrome

Answer 8

TEN and SJS are variants of same condition
Rare, acute, potentially fatal
Antibiotics main cause
Prodromal illness flu-like
- fever, conjunctivitis, sore, cough
Abrupt onset of tender, red skin rash or blister
Usually starts on trunk and spreads to face and limbs (over hours or days)
Blisters merge to form sheets of skin detachment
Mucosal is severe and prominent
Very ill, anxious, and pain

Question 9

Treatment of exanthematous drug eruptions

Answer 9

Identify cause
Emollients
Potent topical steroids S4
Oral antihistamines
Reassurance

Question 10

Treatment of photosensitivity

Answer 10

Stop suspected drug
Strict sun protection strategies
Change time of administration
Moderate-potent topical steroid +/- wet compress
Emollient for symptoms
NSAID (can reduce severity if given <48 hrs)

Question 11

Treatment of TENS/SJS

Answer 11

Possibly fatal (30% Tens, 10% SJS)
Acute phase lasts 8-12 days
Refer to hospital
Identify and stop cause
Specialist needed

Question 12

Referal for drug eruptions

Answer 12

Fixed drug eruptions if lesions are widespread or painful. GP.

Immediate refer TENS/SJS to hospital