Faecal microbiota transplantation: a sui generis biological drug, not a tissue

Responding to Smith et al. (Nature, 2014), this paper argues that for medical use, faecal microbiota transplantation (FMT) should be considered a sui generis biological drug, rather than a tissue. Smith and colleagues' thesis is based on possible undesirable economic consequences of this designation--not on its scientific and conceptual basis. The faecal transplant (including gut microbiota, metabolites, mucus, human cells, viruses, fungi, etc.) is not a tissue; it is of topographic--not cellular--human origin. We consider the donor a bioreactor, producing the faecal substrate of therapeutic interest. The debate is of singular importance as the FDA considers FMT a drug and released a new guidance for public consultation in February 2014, whereas to date the European Medicines Agency has not promulgated its position. The UK's National Institute for Heath and Care Excellence does not consider FMT to involve the transplantation of body tissue, and in March 2014 the French regulatory agency ANSM expressly declared it to be a drug. As FM is a complex and highly variable admixture, its components cannot be completely characterized, and to date, compositional quality cannot be assessed. We consider FMT to be a sui generis biologic drug, albeit one prepared with unconventional raw material under microbiologic control. The possibility of associating identified bacterial species with particular diseases and cultivating selected bacteria of therapeutic interest would certainly define a second generation of microbiome therapeutics, but is still speculative.