We report a patient with acute generalized exanthematous pustulosis (AGEP), which occurred 3 days after ingesting paracetamol and bromhexine. Both were immediately stopped and the rash resolved rapidly. To determine the offending drug responsible for AGEP, an in vitro drug-induced interferon (IFN)-gamma release test was performed using an ELISA technique. Increased IFN-gamma release was observed following in vitro challenge of the patient's lymphocytes with paracetamol or bromhexine (110% and 157% increase, respectively). In vitro challenge with paracetamol or bromhexine in a control patient, treated with paracetamol and bromhexine, did not induce an increase in IFN-gamma. These findings suggest that the patient with AGEP may have polysensitivity to both drugs. The ELISA assessment also demonstrates the relevance of in vitro cytokine release tests in the investigation of such dermatoses.

A man developed acne keloidalis-like lesions in the scalp during treatment with diphenylhydantoin and carbamazepine for epilepsy. These drugs were suspected to play a role in the pathogenesis of this skin disease in an unusual location, based on clinical evidence and on the in vitro test, mast cell degranulation (MCD).

The diagnosis of pustular drug eruptions depends on circumstantial evidence, some characteristic clinicopathological findings and exclusion of alternative diagnoses of other disseminated pustular eruptions. In vitro tests, namely MIF and MCD tests, are a useful diagnostic aid in the identification of the offending drugs.

The role of allopurinol as the drug responsible for the induction of Stevens-Johnson syndrome in our patient was confirmed by in vitro allopurinol-induced IFN-gamma release, which may indicate a drug-specific immune response.