 There are four types of hypersensitivity reactions and many drugs can induce one or more hypersensitivity reactions.The most common type of eruption is a morbilliform (resembling measles) or erythematous rash (approximately 90% of cases).Less commonly, the appearance may also be urticarial, papulosquamous, pustular, purpuric, bullous (with blisters) or lichenoid.