Dermatological Emergencies: Drug Eruptions

Drug eruptions are one of the dermatological emergencies and are quite common to occur. Patients admitted to the hospital with rashes may have those rashes caused by prescribed medications.

Approximately 3% of patients admitted to the hospital have rashes caused by adverse drug reactions. In other cases, cutaneous signs are caused by underlying or intercurrent illness (e.g., viral or bacterial exanthemas and/or internal disease), non-specific reactions to treatment (e.g., sweat-rash), or independent skin disease that was not recognised by hospital staff. True drug reactions are known to mimic other skin diseases. Generally, any type of rash improves once the drug is withdrawn. The recovery time may occur quickly but in some cases can take several weeks.

Adverse drug eruptions can be extremely dangerous, especially in cases of toxic epidermal necrolysis (TEN) and drug hypersensitivity syndrome. The following features indicate that a serious reaction has occurred: skin pain, blistering, high fever, lymphadenopathy, arthritis, abnormal blood count, shortness of breath, and hypertension. Facial and/or mucous membranes are also frequently involved.

Prior to any physician appointment, patients are highly advised to report their full drug history. Physicians typically ask about all medications that have been prescribed and taken in the past three months. This includes all prescribed and non-prescribed medications taken orally, injected, in the form of patches, or applied as creams. Household remedies such as analgesics, hypnotics, or laxatives should also be reported, as should all herbals, vitamins, and homeopathic remedies.

Exanthematous Drug Reactions

Exanthematous drug reactions are also known as toxic erythema. Clinical features include abrupt onset five to ten days after a new drug is prescribed, occurrence of fever and malaise, and possible progression to erythroderma, drug hypersensitivity, or toxic epidermal necrolysis. The rash generally disappears within a week after the suspected drug or series of drugs is withdrawn. Drugs known to cause exanthematous rashes include Penicillins, Erythromycin, Isoniazid, and NSAIDs.

Drug Hypersensitivity Syndrome

A morbilliform eruption involving one or more internal organs in the presence of fever results in drug hypersensitivity syndrome (DHS). It carries a mortality rate of 10%.

Drug-Induced Urticaria

Drug-induced urticaria occurs with or without angioedema and can last for three weeks after the initial exposure. It may be caused by type 1 hypersensitivity (e.g., penicillin) or direct release of inflammatory mediators from mast cells as an initial reaction to drug exposure (e.g., aspirin, NSAIDs, muscle relaxants, opiates). Drugs known to cause urticaria include Penicillins, cytostatic agents, ACE inhibitors, calcium channel blockers, and Sulphonamides.

Fixed Drug Eruptions

Fixed drug eruptions (FDE) refer to a single plaque or multiple plaques that appear within a few hours, sometimes followed by blisters. Mucosal surfaces such as the lips and genitals are commonly affected. FDE resolves within a few days but leaves purple hyperpigmentation and can re-erupt at the same site upon re-exposure to the causative drug.

Drug-Induced Purpura

Purpura refers to skin bleeding caused by drugs. This includes allergic or cytotoxic thrombocytopenia, capillaritis, and overdose of anticoagulants, among other mechanisms.

Drug-Induced Photosensitivity

Drug-induced photosensitivity is caused by toxic and/or immunological mechanisms arising from either systemic or topical exposure to medication. The rash affects sites of light exposure (UVA) but may spare areas such as the face and hands. Phototoxic reactions can affect any person if the dose is sufficiently high and typically present in the form of sunburns.

Drug-Induced Pigmentation

Drug-induced pigmentation arises from deposition of melanin (e.g., ACTH, phenytoin), exogenous pigment (minocycline), or haemosiderin (minocycline). Approximately 75% of patients experience pigmentary changes on exposed sites. Clofazimine results in reddish-brown pigmentation on light-exposed areas and in excretions such as sweat.

Management of Drug Eruptions

In the case of a suspected drug eruption, it is highly advised that the responsible drug be discontinued and that drugs belonging to the same pharmacological class also be avoided. Patients with drug eruptions are typically treated with emollients, hydrocortisone lotion, or oral antihistamines.