Amoxicillin-induced flare in patients with DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms): report of seven cases and demonstration of a direct effect of amoxicillin on Human Herpesvirus 6 replication in vitro.

Amoxicillin is known to induce exanthema in patients with EBV-induced infectious mononucleosis. It is widely recognized that the reactivation of herpesviruses, including HHV-6 (Human Herpesvirus 6) and EBV (Epstein Barr virus) is associated with DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms). We report 7 cases of amoxicillin-induced flare in patients with DRESS induced by other drugs and investigate whether amoxicillin may have a direct effect on HHV-6 replication in vitro. 7 cases of DRESS with amoxicillin-induced flare were retrospectively analysed. The influence of amoxicillin on HHV-6 HST strain replication was studied in vitro in a human T lymphoblastoid MT4 cell line. The viral replication was quantified by immunofluorescence assay and by real-time polymerase chain reaction (PCR). Comparisons were performed using the Student's t test. Amoxicillin-induced flare was observed in 7 patients with DRESS induced by other drugs. In two cases HHV-6 reactivation was studied and was demonstrated by PCR. Amoxicillin neither modified cell viability nor cell proliferation for the range of tested concentrations. Amoxicillin increased the replication of HHV-6 at 25 microgmL-1 and 50 microgmL-1. Amoxicillin may induce a flare of DRESS, possibly by acting directly on herpesvirus replication.