Drug Allergy Flashcards
Name the four types of Drug Allergies
Any drug can cause a skin reaction but some classes of drugs are characteristically associated with certain types of reaction.
Not all dermatological problems produce visible signs. The skin may appear normal with marked pruritus. It may be difficult to decide if the drug is really the cause of the problem and to withdraw it, especially if it is providing important treatment. Early withdrawal of the offending drug may limit its adverse effects.
Many of these reactions are immunological in origin. Possibly the drug acts as a hapten and binds to proteins to form a structure that the immune system recognises as ‘not self’. Most immunologically mediated reactions can be allocated to one of the Gel and Coombs’ classes of hypersensitivity:[1]
Type I is mediated by IgE and results in urticaria, angio-oedema and anaphylaxis. They are often caused by proteins and especially insulin.
Type II is a cytotoxic reaction which produces haemolysis and purpura. They are caused by penicillin, cephalosporins, sulfonamides and rifampin.
Type III is immune complex reactions, which result in vasculitis, serum sickness and urticaria. They can be caused by salicylates, chlorpromazine and sulfonamides.
Type IV is delayed-type reactions with cell-mediated hypersensitivity, which result in contact dermatitis, exanthematous reactions and photoallergic reactions. These reactions are the most common and are usually caused by topical applications. Antibodies can be demonstrated in fewer than 5% of drug reactions, as the problem is cell-mediated. Type IV reactions are not dose-dependent. They usually begin one to three weeks after medication is started. This is significantly slower than most other reactions. There may be eosinophilia and they may recur if other drugs that are chemically related are used.
What are the four allergic patterns identified by the National Institute for Health and Care Excellence (NICE)?
Allergic patterns identified by the National Institute for Health and Care Excellence (NICE)[2]
Immediate (developing within an hour) - anaphylaxis, urticaria, exacerbation of asthma (eg, by exposure to NSAIDs).
Non-immediate without systemic involvement (6-10 days after first drug exposure or within three days of second exposure) - widespread red macules or papules (exanthema‑like) or fixed drug eruption.
Non‑immediate reactions with systemic involvement (2-6 weeks after first drug exposure or within three days of second exposure) - drug reaction with eosinophilia and systemic symptoms (DRESS) or drug hypersensitivity syndrome (DHS). The features are widespread red macules, papules or erythroderma, fever, lymphadenopathy, liver dysfunction and eosinophilia.
Toxic epidermolysis (7-14 days after first drug exposure or within three days of second exposure - see below.
Stevens-Johnson syndrome (7-14 days after first drug exposure or within three days of second exposure ) - see below.
Acute generalised exanthematous pustulosis (AGEP) (3-5 days after first drug exposure) - characterised by:widespread pustules, fever, neutrophilia.
What describes Acneform lesions and what are the usual drug causes?
Acneform lesions
These are different from acne vulgaris in that they tend to be over the upper body rather than the face and there are no comedones.
Typical drugs are corticosteroids, halogens, haloperidol, hormones, isoniazid, lithium, phenytoin and trazodone:
The halogens are usually bromide or iodide.
The hormones may be anabolic steroids taken illicitly by bodybuilders or some athletes. Progestogens can also be a problem. This tends to be in low-oestrogen, high-progestogen oral contraceptive pills rather than progestogen-only pills or depot and implant contraceptives.
Describe Acute generalized exanthematous pustulosis (AGEP)
This produces an acute onset of fever and generalised scarlatiniform erythema with many small, sterile, non-follicular pustules. It appears like pustular psoriasis.
Most cases are caused by antibiotics, often in the first few days of administration.
Some may be viral infections, mercury exposure, or UV radiation. They resolve spontaneously and rapidly, with fever and pustules lasting 7-10 days before desquamation over a few days.
Typical drugs include beta-lactam antibiotics, macrolides and less commonly, a wide variety of drugs including paracetamol, carbamazepine, tetracyclines, diltiazem, furosemide, hydrochlorothiazide, hydroxychloroquine, nifedipine, phenytoin, pseudoephedrine, ranitidine, sertraline, simvastatin, terbinafine and vancomycin.
