Drugspecific Rashes

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Despite great variability, some hints at drug-specific

Drugs applied locally or taken systemically often bardie R A, Savin J A1979 British Medical Journal: 1935, to cause rashes. These take many different forms and whom we are grateful for this quotation and classification.

or characteristic rashes from drugs taken systemically, can be discerned, as follows:

Acne and pustular: e.g. corticosteroids, androgens, Ciclosporin, penicillins.

Allergic vasculitis: e.g. sulphonamides, NSAIDs, thiazides, chlorpropamide, phenytoin, penicillin, retinoids

Anaphylaxis: x-ray contrast media, penicillins, ACE inhibitors.

Bullous pemphigoid: frusemide (and other sulphonamide-related drugs), ACE inhibitors, penicillamine, penicillin, PUVA therapy.

Eczema: e.g. penicillins, phenothiazines.

Exanthematic/maculopapular reactions are the most frequent; unlike a viral exanthem the eruption typically starts on the trunk; the face is relatively spared. Continued use of the drug may lead to erythroderma. They commonly occur at about the ninth day of treatment (or day 2-3 in previously exposed patients), although onset may be delayed until after treatment is completed; causes include antimicrobials, especially ampicillin, sulphonamides and derivatives (sulphonylureas, frusemide (furosemide) and thiazide diuretics). Morbilliform (measles-like) eruptions typically recur on rechallenge.

Erythema multiforme: e.g. NSAIDs, sulphonamides, barbiturates, phenytoin.

Erythema nodosum: e.g. sulphonamides, oral contraceptives, prazosin.

Exfoliative dermatitis and erythroderma: gold, phenytoin, carbamazepine, allopurinol, penicillins, neuroleptics, isoniazid.

Fixed eruptions are eruptions that recur at the same site, often circumoral, with each administration of the drug: e.g. Phenolphthalein (laxative self-medication), sulphonamides, quinine (in tonic water), tetracycline, barbiturates, naproxen, nifedipine.

Hair loss: e.g. cytotoxic anticancer drugs, acitretin, oral contraceptives, heparin, androgenic steroids (women), sodium valproate, gold.

Hypertrichosis: corticosteroids, Ciclosporin, doxasosin, minoxidil.

Lichenoid eruption: e.g. ß-adrenoceptor blockers, chloroquine, thiazides, frusemide (furosemide), Captopril, gold, phenothiazines.

Lupus erythematosus: e.g. hydralazine, isoniazid, procainamide, phenytoin, oral contraceptives, sulfazaline.

Purpura: e.g. thiazides, sulphonamides, sulphonylureas, phenylbutazone, quinine. Aspirin induces a capillaritis (pigmented purpuric dermatitis).

Photosensitivity: see above.

Pemphigus: e.g. penicillamine, Captopril, Piroxicam, penicillin, rifampicin.

Pruritus unassociated with rash: e.g. oral contraceptives, phenothiazines, rifampicin (cholestatic reaction).

Pigmentation: e.g. oral contraceptives (chloasma in photosensitive distribution), phenothiazines, heavy metals, amiodarone, chloroquine (pigmentations of nails and palate, depigmentation of the hair), minocycline.

Psoriasis may be aggravated by lithium and antimalarials.

Scleroderma-like: bleomycin, sodium valproate, tryptophan contaminants (eosinophila-myalgia syndrome).

Serum sickness: immunoglobulins and other immunomodulatory blood products.

Stevens-Johnson syndrome and toxic epidermal necrolysis:9 e.g. anticonvulsants, sulphonamides, aminopenicillins, oxicam NSAIDs, allopurinol, chlormezanone, corticosteroids.

Urticaria and angioedema: e.g. penicillins, ACE inhibitors, gold, NSAIDs, e.g. aspirin, codeine.

Recovery after withdrawal of the causative drug generally begins in a few days, but lichenoid reactions may not improve for weeks.

Diagnosis. The patient's drug history may give clues. Reactions are commoner during early therapy (days) than after the drug has been given for months. Diagnosis by readministration of the drug (challenge) is safe with fixed eruptions, but not with others, particularly those that may be part of a generalised effect, e.g. vasculitis. Patch and photopatch tests are useful in contact dermatitis, for they reproduce the causative process but should be performed only by those with special experience. Fixed drug eruptions can sometimes be reproduced by patch testing with the drug over the previously affected site.

9 Roujeau C-J et al 1995 New England Journal of Medicine 333:1600

Intradermal tests introduce all the problems of allergy to drugs, e.g. metabolism, combination with protein, fatal anaphylaxis (see p. 143).

Treatment. Remove the cause; use cooling applications and antipruritics; use a histamine Hj receptor blocker systemically for acute urticaria; give an adrenal steroid for severe cases.

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