Fixed drug eruption (FDE) is a cutaneous adverse drug reaction that recurs at the same body site each time the individual is re-exposed to the culprit drug. One or more sharply demarcated, red or violaceous patches that are typically round develop within minutes to hours of exposure to the inciting drug. These may vary from 0.5 to several centimeters in size. They are usually asymptomatic, although burning, pain, or pruritus may occur. While any cutaneous surface may be affected, the oral and anogenital mucosa are most frequently involved. In women, the patches of FDE may affect the vagina or vulva. FDE involving the genital mucosa in women can be challenging as it may present as an acute or chronic, recurrent vulvitis that is not responsive to topical steroid therapy but rapidly resolves upon cessation of the offending agent.

FDE is most commonly solitary, but some individuals may develop multiple patches. There may be an increasing number of patches seen with each exposure. Healing with postinflammatory hyperpigmentation is common.

Numerous drugs have been implicated in causing FDE. The most commonly associated drug classes for FDE in the anogenital region are also the most frequently seen culprit medications for FDE in general. These medication classes include antibiotics, in particular sulfonamides, trimethoprim, and tetracyclines, and NSAIDs, including naproxen, ibuprofen, and celecoxib. Other drugs implicated in FDE include amoxicillin, erythromycin, metronidazole, fluconazole, paracetamol (acetaminophen), cetirizine, hydroxyzine, methylphenidate, oral contraceptives, quinine, and phenolphthalein. Biologic agents including ustekinumab, adalimumab, and abatacept have been reported to cause fixed drug eruptions. A nonpigmenting version of this condition is seen with pseudoephedrine.