Drug Allergy and Urticaria

Urticaria: A skin reaction characterized by pruritic, red wheals
• Lesions may vary from a small point to a large area
• Individual lesions rarely last more than 24 hours
• When deep dermal and subcutaneous tissues are also swollen, this reaction is known as
angioedema
• Angioedema may involve mucous membranes and may be part of a life-threatening
anaphylactic reaction
• Urticarial lesions along with pruritus and morbilliform (or maculopapular) eruption are
among the most frequent types of cutaneous reactions to drugs
Causes
• Drug Induced Urticaria
May be caused by three mechanisms
IgE-dependent mechanism
Circulating immune complexes (serum sickness)
Non-immunologic activation of effector pathways
It may also be idiopathic (unknown cause)
Clinical Features, Diagnosis and Treatment of Drug Allergies
Clinical Features
• IgE-dependent urticarial reactions usually occur within 36 hours although it can also
occur within minutes.
• Reactions occurring within minutes to hours of drug exposure are termed immediate
reactions whereas those occurring 12 to 36 hours after drug exposure are termed
accelerated reactions.
• Immune complex induced urticaria associated with serum sickness usually occurs from 6
to 12 days after first exposure.
• In this syndrome urticarial eruption may be accompanied by
Fever
Haematuria
Arthralgias
Hepatic dysfunction, and neurologic symptoms
• Certain drugs such as NSAIDs, angiotensin-converting enzyme (ACE) inhibitors and
radiographic dyes may induce urticarial reactions, angioedema and anaphylaxis in the
absence of drug-specific antibody.
• Although ACE inhibitors, aspirin, penicillin and blood products are the most frequent
causes of urticarial eruptions, urticaria has been observed in association with nearly all
drugs.
• Drugs also may cause chronic urticaria which lasts more than 6 week. Aspirin frequently
exacerbates this problem.
Treatment
• Urticaria or angioedema depends on the severity of the reaction and the rate at which it is
evolving.
• In severe cases especially with respiratory or cardiovascular compromise epinephrine is
the mainstay of therapy but its effect is reduced in patients using beta blockers.
• For more seriously affected patients treatment with systemic glucocorticoids sometimes
intravenously administered are helpful.
• In addition to drug withdrawal for patients with only cutaneous symptoms and without
symptoms of angioedema or anaphylaxis oral antihistamines are usually sufficient.
Diagnosis and Management of Drug Reactions
• Possible causes of an adverse reaction can be assessed as
Definite
Probable
Possible or unlikely
• Based on six variables
Previous experience with the drug in the general population
Alternative etiologic candidates
Timing of events
Drug levels or evidence of overdose
Patient reaction to drug discontinuation
Patient reaction to rechallenge
Management of Drug Allergies
• Drug discontinuation
• Mild rash could be treated with H1 anti-histamines such as diphenhydramine or
chlorpheniramine
• Treatment with systemic steroids sometimes intravenously administered are helpful for
severe drug reactions
Definition, Aetiology, Clinical Features, Investigations and Treatment of
Boil
• A boil: Is a red swollen painful lump under the skin that is caused by an infection. Boil
often starts as an infected hair follicle where bacteria forms pocket of pus which
eventually drain out through the skin.
Aetiology
• The causation agents include
Bacteria Staphylococcus aureus or other bacteria which become secondary to ingrowing
hair, splinter or foreign object lodged in the skin and plugged on the sweat glands or oil
ducts.
Risk Factors to Infection
• Diabetes
• Poor nutrition
• Poor hygiene
• Obesity
• Intravenous drug use
• Immunosuppressant system
• Exposure to hard chemicals
Clinical Features
• Skin lump or bump that is red, swollen and tender
• The lump becomes larger more painful and softer overtime
• Pockets of pus may form on top of the boil
Investigations
• History and performing physical examination
• Bacterial culture to know type of organisms and their sensitivity
Treatment
• Do incision and drainage
• Give systemic antibiotics to which Staphylococcus aureus is sensitive e.g. penicillin
• Application of compressed hot application for 20 minutes in 3-4 times a day will ease the
pain and help to bring the pus to the surface for drainage
• Do not lance (pop) the boil because this can spread the infection and make it worse
           
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