When rash challenges treatment: reintroducing cystic fibrosis modulator therapy safely.

Various adverse reactions to elexacaftor/tezacaftor/ivacaftor (ETI) therapy have been documented in the literature. Here, we present the first reported case in Croatia of severe rash following ETI therapy in a 19-year-old female cystic fibrosis (CF) patient. There were two attempts to introduce ETI therapy, spaced two months apart, both of which resulted in diffuse maculopapular rash, in the second attempt, the rash appeared on the same day as re-initiation. Given the clinical benefits of ETI treatment, andinspired by several case reports on drug desensitization, in July 2023, we started the patient on a modified 3-day-tolerance induction protocol which was successful.