Benserazide-induced diarrhea – A retrospective clinical study

BACKGROUND: Although diarrhea has been reported as a side effect of L-3,4- dihydroxyphenylalanine (L-DOPA)/benserazide, it is largely unknown and unrecognized, presumably because it is very rare. There is almost no literature on benserazide-induced diarrhea (BID), no pharmacological explanation and, crucially, no treatment recommendation. This can lead to physicians misdiagnosing BID, for example as colitis, and initiating misguided and ultimately ineffective drug treatments. Or it can lead to erroneous assumptions about a general intolerance and subsequent discontinuation of L-DOPA medication – for lack of a better solution – at the high price of living with the recurring symptoms of Parkinson’s disease. Thus, our study aims to fill these gaps, beginning with a treatment recommendation: A simple switch to LDOPA/ carbidopa has proven to be an effective solution in virtually all cases of BID, usually leading to full remission within days. Finding a possible pharmacological explanation was the next objective of this study. METHODS: We retrospectively analyzed 50 case files of patients with BID, searching for patterns that could potentially explain this intolerance. RESULTS: The most frequent concomitant disease was hypertension, likely due to high average age. Beta-blockers and acetylsalicylic acid were the most frequent concomitant medications. Otherwise, no conspicuous pattern emerged in this seemingly rather heterogeneous sample. CONCLUSIONS: Plasma protein binding (PPB) was suspected as a key difference between benserazide and carbidopa that might potentially explain why some patients can tolerate carbidopa but not benserazide. However, reports on PPB of carbidopa and benserazide vary wildly from one source to another, making definitive conclusions impossible.