Drug eruptions
Reactions to drugs are common and often produce an eruption. Almost any drug can result in any reaction, although some patterns are more common with certain drugs. Not all reactions are ‘allergic’ in nature.
Aetiopathogenesis
Drug-induced skin reactions have several possible mechanisms:
Clinical presentation
Drug eruptions present in many guises and come into the differential diagnosis of several rashes. It is vital to obtain a detailed drug ingestion history. This must include ‘over-the-counter’ preparations (e.g. for headaches or constipation) not normally regarded as ‘drugs’ by the patient. A drug introduced during a 2-week period before the eruption starts must be viewed as the most likely culprit, although a reaction may occur to a drug taken safely for years. The majority of drug eruptions fit into a defined category (Table 1). The most severe and characteristic ones are outlined below. Other patterns are discussed in the relevant chapters. Drugs including non-steroidals or angiotensin-converting enzyme (ACE) inhibitors, but especially lithium and chloroquine, can exacerbate existing psoriasis. Other agents, e.g. beta-blockers and gold, may provoke a psoriasis-like eruption.
Table 1 Patterns of drug-induced skin disease
| Drug eruption | Description | Drugs commonly responsible |
|---|---|---|
| Acneiform | Like acne: papulopustules, no comedones | Androgens, bromides, dantrolene, isoniazid, lithium, phenobarbital, quinidine, steroids |
| Bullous | Various types; some phototoxic, some ‘fixed’ | Barbiturates (overdose), furosemide, nalidixic acid (phototoxic), penicillamine (pemphigus-like) |
| Drug-induced exanthem | Commonest pattern (see text) | Antibiotics (e.g. amoxicillin), proton pump inhibitors, gold, thiazides, allopurinol, carbamazepine |
| Eczematous | Not common; seen when topical sensitization is followed by systemic treatment | Neomycin, penicillin, sulphonamide, ethylenediamine (cross-reacts with aminophylline), benzocaine (cross-reacts with chlorpropamide), parabens, allopurinol |
| Erythema multiforme | Target lesions (p. 82) | Antibiotics, anticonvulsants, ACE inhibitors, calcium channel blockers, non-steroidals |
| Erythroderma | Exfoliative dermatitis (p. 44) | Allopurinol, captopril, carbamazepine, diltiazem, gold, isoniazid, omeprazole, phenytoin |
| Fixed drug eruption | Round red–purple plaques recur at same site | Antibiotics, tranquillizers, non-steroidals, phenolphthalein, paracetamol, quinine |
| Hair loss | Telogen effluvium (p. 66) Anagen effluvium (p. 66) | Anticoagulants, bezafibrate, carbimazole, oral contraceptive pill, propranolol, albendazole, cytotoxic drugs, acitretin |
| Hypertrichosis | Excess vellus hair growth (p. 66) | Minoxidil, ciclosporin, phenytoin, penicillamine, corticosteroids, androgens |
| Lupus erythematosus (LE) | LE-like syndrome (p. 80) |
