Our evidence suggests that current regulations for clinical trials and the manufacturing of medicines are unlikely to be effective for phages as they are for other drugs or antibiotics. This is because the current regulatory approach to testing and manufacturing medicines is based on a single consistent formulation being shown to have a demonstrable effect. This does not accord with the optimal use of phages which require considerable flexibility in terms of the specificity required for 60 The antimicrobial potential of bacteriophages individual patients. There are a number of different medical scenarios where the current regulations will struggle to cope with this need for specificity that mitigates against generic testing. These include: • the requirement for individual phage strains that are specific to the species and even strain genotype of the bacteria they seek to inhibit, which could be almost limitless and impossible to test in advance; • the need for multiple unique formulations of phages, often in conjunction with antibiotics and other drugs, to target infections in individual patients with specific microbiota, which might not be anticipated in traditional clinical trials; • in the future, pre-tested generic phages that have met regulatory standards may not be able to inhibit bacterial growth, necessitating adaptation which may be beyond inflexible regulations; • the specificity required to target a particular infection in a single human could require gene editing of phages, with current regulations implying that each new formulation would require full clinical trials each time, which would not be timely, cost effective, efficient or possible in terms of generating significant clinical data if each use is unique; • the use of double-blind clinical trials and control groups would be problematic if they related to a unique combination of phages produced for a single patient.