see also:

• acute generalized non-vesicular non-purpuric rashes covering most parts of the body
• acute rashes in adults

• DRESS syndrome usually starts 2–8 weeks after the offending drug is started, most often around 2–6 weeks, this is in contrast to most other drug reactions as the onset is delayed compared with most simple drug rashes, which often appear much earlier
• it can appear sooner on re-exposure, and in some cases symptoms continue or worsen even after the drug is stopped

• aromatic anticonvulsants and other antiepileptics cause the majority of cases eg. carbamazepine, phenytoin, lamotrigine, and phenobarbitone
• allopurinol
• non-steroidal anti-inflammatory drugs (NSAIDs)
• certain antibiotics such as such as vancomycin, minocycline, trimethoprim-sulfamethoxazole, and sulphonamides

• rash
  • usually causes a widespread morbilliform or maculopapular rash that often starts on the trunk or face and then spreads to much of the body. It is commonly itchy, may be red and confluent, and can become purplish, swollen, or even peeling/exfoliative as it progresses.
• other features which may be present:
  • facial oedema
  • fever
  • lymphadenopathy
  • occasionally mucosal involvement
  • hepatitis
  • nephritis
• eosinophilia and atypical lymphocytes on blood film

• essentially clinical based on drug exposure, clinical features and blood film while excluding other causes such as EBV, CMV, HHV-6, hepatitis
• RegiSCAR scoring system

• FBE, U&E, LFTs, CRP, and consider EBV, etc.
• IV fluids if dehydrated
• usually require inpatient Mx