[Drug-induced photosensitivity]

Photodermatosis are dermatoses where there is an abnormally exaggerated sensitivity to sunlight, termed photosensitivity, that is often drug-induced. Such drug-induced photosensitivity is due to the mechanism of photosensitivization that induces two types of reaction, phototoxic and photoallergic. The phototoxic reaction is photochemical, irritative and common, and can occur in any individual without any particular predisposition. The photoallergic reaction is a photoimmunologic, cell-mediated hypersensitivity reaction. It is much more rare and occurs only in some individuals with predisposition. Clinically, the phototoxic reaction usually manifests by a cutaneous "sunburn" type eruption, and the photoallergic reaction by eczema. Photosensitizing drugs are numerous: antibiotics, nonsteroid anti-inflammatory drugs, diuretics, antimitotic drugs, psychiatric drugs, amiodarone, calcium channel blockers, fibric acid derivatives, etc. Diagnosis is based on recognition of an eruption localized in zones exposed to sunlight occurring in the context of photosensitizing drug intake, correlated with the results of photobiological laboratory investigations.