What other tests are indicated in the workup of fixed drug eruptions (FDE)?

Updated: Oct 09, 2020
  • Author: David F Butler, MD; Chief Editor: Dirk M Elston, MD  more...
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Patch testing and oral provocation have been used to identify the suspected agent and check for cross-sensitivities to medications. [58, 59, 60, 61] A refractory period has been reported in fixed drug eruption; therefore, a delay before and between patch testing and oral provocation is recommended. One study used an 8-week time window after lesion resolution and between tests, which yielded positive results. [62] Patch testing must be performed on a previously involved site; otherwise, a false-negative result is likely. [59] Some locations may be inappropriate for patch testing; thus, clinical discretion is advised. Once patch testing is complete, oral provocation should follow, with the least likely culprits and the negative patch test agents first, followed by more likely causes. Oral provocation is thought to be the only reliable way to diagnose fixed drug eruption.

Patch testing is particularly efficacious in identifying a putative cause of the reaction when nonsteroidal anti-inflammatory agents are suspected, but patch testing is not helpful in discerning reactions to antibiotics and allopurinol. [63]

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