**7. Stratification of patients with respect to gut microbiota in clinical trials**

It has recently been discovered that the gut microbiota plays a major role in the human metabolome (Nicholson et al 2005), and that the effects of drugs can be dependent on the gut microbiota (Clayton et al 2009). Combined with recent evidence that the human microbiome may consist of only three enterotypes (Arumugam et al 2011), diagnostics of such enterotypes is expected to provide important information with respect clinical trials. Enterotypes represent clusters of bacteria with a high frequency of co-occurrence, suggesting different states of the microbiota with different functionalities. There are several evidences for gut microbiota metabolism of important drugs, such as drugs against Alzheimer (Pieper et al., 2009)

Combined with the enterotype knowledge we believe that stratification will be a highly interesting field for gut microbiota diagnostics. This will be in line with the recent developments of personalized drugs –drugs adapted to individuals. Clearly, a major part of defining an individual would be the composition of gut microbiota. Information about the gut microbiota may therefore help to increase the success rate of clinical trials.
