Interaction with St. John's wort due to exposure with blackcurrant aroma? How not to present a case report of an adverse event.

Background: Adverse events case reports are important for signal generation in pharmacovigilance. They require a thorough collation of the facts, otherwise they may lead to erroneous conclusions which may conceal other treatment-related causes of the observation. Methods: We describe a case report from the literature that arrives at an erroneous conclusion merely from taking insufficient care when collating and interpreting the facts: The authors of the case report confused blackcurrant (Ribes nigrum) with St. John's wort preparation (Hypericum perforatum) and erroneously assumed that the intake of a herbal preparation was responsible for a drop in serum levels of everolimus. Results: The clinical observations in this case report may actually reflect a potentially lethal situation emerging from the prescribed medication everolimus. St. John's wort preparations rich in hyperforin do in fact reproducibly lead to the decrease of blood levels of medications metabolized through cytochrome P450 subtype 3A4. However, a case report requires more care than just ascribing the blame to something seemingly well-known. Conclusion: The readers of this report might have profited more from the description of the risks of treating graft-versus-host disease with everolimus, and the action to be taken in case of potentially severe adverse reactions to everolimus.