Drug eruptions: approaching the diagnosis of drug-induced skin diseases

Journal of Drugs in Dermatology, June, 2003 by Simon Nigen, Sandra R. Knowles, Neil H. Shear

In comparison, drug-induced photoallergic dermatitis has an immunologic basis and requires previous exposure to the photosensitizing agent. This reaction appears within 24 hours of antigenic challenge. In this eruption, absorption of the UV light energy enables the drug to conjugate with a carrier protein to form a complete antigen. Once the antigen is formed, the mechanism of photoallergy is identical to that of an allergic contact dermatitis.

It preferentially affects the sun-exposed areas like the face (especially the nose, cheeks, forehead), the rims of the ears, the V region of the neck and upper chest and the dorsum of the hands and arms, and spares the submental and retro-auricular regions and upper eyelids. In some patients, a generalized eruption can arise reflecting an autoeczematization phenomenon.

Diagnosis of a photosensitive eruption can be done by a careful history and examination. The recent exposure of a causative drug with the distribution of the eruption is characteristic. Photopatch testing can confirm a photoallergic or phototoxic eruption. Treatment includes avoidance of the offending photosensitizing agents and/or sunlight exposure. Sunscreen with broad-spectrum coverage (both UVA and UVB) is necessary. Symptomatic treatment with topical corticosteroids and oral antihistamines is helpful if pruritus and discomfort are present. Oral steroids are reserved for only the most severely affected patients.

Conclusion

After a cutaneous drug eruption has been diagnosed and treated, clear information must be provided to the patient regarding his/her drug rash. The name of the medication, potentially cross-reacting drugs and drugs which can be safely taken are an important part of the evaluation.

The patient should also be advised to enroll in the MedicAlert program and to wear a bracelet detailing the nature of the allergy. Patient records should be appropriately labeled.

The predisposition to some drug-induced eruptions may be genetic, and family counseling is part of the care plan. This can be important especially in SJS, TEN, drug hypersensitivity syndromes and SSLRs.

Finally, cutaneous drug reactions should be reported to the manufacturer and regulator agency especially if the skin eruption is rare, serious or unexpected.