subject: Types of drug eruption [print this page] Types of drug eruption Types of drug eruption
Urticaria The mechanisms whereby a drug can cause urticariainclude IgE-mediated immediate hypersensitivity, immunecomplex-mediated generation of activated complementcomponents (serum sickness), a direct action on mast cellscausing them to release histamine, and modulation ofarachidonic acid metabolism. The drugs commonly implicatedin urticaria are: Penicillin and relatedantibiotics X-ray contrast media Enzymes Blood products Opiates Non-steroidal antiinflammatorydrugs Pollen vaccines Iodides.Angioedema and anaphylaxis may accompany urticaria,particularly when the drug has been injected, and can belife-threatening.Urticaria usually begins within minutes or hours of thedrug being given, but when it is immune complex-relatedit occurs several days after the challenge and is often associatedwith fever, lymphadenopathy, joint symptoms andhaematuria as a result of renal damage.
Morbilliform eruption A widespread, symmetrical, blotchy, maculopapular erythematous rash is probably the commonestdrug eruption. There is often a mild fever, but serious consequencesare uncommon. The mechanism is usuallyobscure but does involve delayed hypersensitivity in somecases, especially when the onset is within a few days of thedrug being started. Morbilliform eruptions usually beginwithin a week of the onset of the drug, and may progressto erythroderma if the drug is continued.
Ampicillin, amoxicillin and derivatives, e.g. talampicillin,are common causes, especially when the patient has infectiousmononucleosis or lymphatic leukaemia, or is alsotaking allopurinol, and can begin up to a few days after theantibiotic has been stopped. The common causes of morbilliform(exanthematic) drug eruptions are: Allopurinol Penicillamine Antituberculous drugs Penicillins Captopril Phenothiazines Carbamazepine Phenylbutazone Gold salts Sulphonamides H2 antihistamines Thiazides
Erythroderma When caused by a drug, erythroderma, or exfoliative dermatitis, tends to begin several weeks after the drughas been started. Important causes of drug-induced erythrodermaare: Allopurinol Carbamazepine Phenytoin Isoniazid Lithium Gold salts Chloroquine Barbiturates p-aminosalicylic acid Captopril Sulphonamides Methyldopa.
Erythema multiforme Erythema multiforme is a reaction distinguishedby target lesions. Most cases are not due to drugs. The commonestdrugs to cause erythema multiforme are: Sulphonamides Phenytoin Phenylbutazone Barbiturates Penicillins Carbamazepine Rifampicin Gold salts.
Toxic epidermal necrolysis Toxic epidermal necrolysis is a rare drug reaction whichhas a high mortality. There is often a brief prodrome ofmalaise and fever, followed by widespread, tender erythematousareas which then blister. Large sheets of epidermisreadily rub off with light pressure, to leave painful denudeddermis. Mucous membranes as well as skin may beinvolved. Fluid imbalance, septicaemia and pneumonia arethe most common problems.Differentiation from staphylococcal scalded skin syndrome can be made histologically on a blister roofbecause in toxic epidermal necrolysis the roof consists ofthe whole epidermis. Butazones, Sulphonamides, allopurinol,gold salts and phenytoin are examples of drugs thatcan cause the syndrome, which can also be due to infections,graft-versus-host disease and lymphoma.Management is similar to that of widespread burns, with treatment of fluid and protein loss and of infection
Photosensitivity The most common photosensitivity drug reaction resemblessunburn and is usually phototoxic, i.e. does not involveimmunological mechanisms. Occasionally drugs producephotoallergic reactions which may look like eczema onlight-exposed skin. Drugs which can induce phototoxic andphoto-allergic reactions include:PhenothiazinesThiazidesSulphonamidesTetracyclinesSulphonylureas Nalidixic acid (bullous) Amiodarone Azapropazone Protriptyline Psoralens.Drugs can also induce photosensitive diseases, e.g. procainamidecan induce lupus erythematosus, and isoniazid pellagra.
Fixed drug eruptionThe characteristic feature of a fixed drug eruption is thatinflammation occurs in exactly the same place or fewplaces each time the drug is taken. The reaction is usuallya round red patch, which may blister, and afterthe inflammation has subsided there is often prolongedhyperpigmentation.The causes change with variations in drug use, but arecent survey in the UK identified several commonoffenders - paracetamol, non-steroidal anti-inflammatorydrugs, fluconazole, terbinafine, sulfasalazine, tetracylines,trimethoprin, diltiazem and proton pump inhibitors.
VasculitisDrug-induced vasculitis , usually in the form ofpalpable purpura, and often with urticarial and blisteringlesions, can be accompanied by similar lesions in otherorgans and may be a serious illness. The commonest drugsto cause allergic vasculitis are:Allopurinol SulphonamidesThiazides HydralazinePhenytoin QuinidineThiouracil Captopril.Non-steroidal antiinflammatory drugs
Erythema nodosum Drugs are rarely responsible for erythema nodosum, andother causes should be sought. Oral contraceptivesand Sulphonamides are the drugs most likely to be involved.
Pigmentation changes induced by drugsColour change can be produced by depositionof the drug in the skin and mucous membranes,stimulation of melanin production and alteration of thedistribution of pigment so as to make it more apparent,as in postinflammatory hyperpigmentation. Thehyperpigmentation after fixed drug eruption may be thepresenting feature. In some situations the pigmentationis only evident in light-exposed skin. In many examplesof drug-related pigment change the mechanism is unknown.
