Phage therapy: two paths to approval

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Phage therapy is the use of viruses that infect bacteria as antibacterial treatments. A simple version of the history of phage therapy in much of the West follows an arc of enthusiastic embrace in the 1920s and 1930s, to disappointment as results were seen to be erratic and unpredictable, especially in the face of more reliable antibiotics being introduced at the same time [1,2]. This was followed by a long period of disappearance. In the last few decades, especially in light of the increasing appearance of antibiotic resistant bacteria, there has been renewed interest in phage therapy. I should note that for this essay, I will be focusing on phage therapy as a medical treatment and not on the use of phages as biocontrol agents for plant diseases, disinfection of foods and other materials and more. 

During the fallow period when phage therapy was not in use, a regulatory system developed in many countries to improve the efficacy and safety standards of medical treatments [3].  This system was developed for drugs that do not change during their development and use. It has proven challenging to test phages under this paradigm for multiple reasons including the phages’ potential to evolve during treatment so that the phages at the end of a treatment may not be identical to the phages used to initiate treatment. To their credit, regulators have recognized this issue and some definitions have been broadened to better reflect the biological nature of phages [4].

Multiple companies now have clinical trials underway to test phages to treat a variety of bacterial infections [4,5]. These trials may use single phages or mixtures of different phages often called phage cocktails. The advantage of phage cocktails is that they generally will contain phages that infect more types of bacteria, so a cocktail can treat more strains or species and thus have broader applications [6]. Because this approach to phage therapy is following a relatively standard regulatory pathway I will refer to it as the standardized drug approach (SD).

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