Phage therapy gets first global clinical guidelines

An international team led by the German Society for Infectious Diseases (DGI) has published the first internationally coordinated clinical guidelines for personalized phage therapy, a treatment that uses bacteria-killing viruses to attack harmful bacteria. The consensus statement appeared in the journal Nature Medicine.

The effort involved 20 professional organizations, 18 international experts including representatives from regulatory agencies, and two patient advocacy organizations. Together they set out more than 60 recommendations covering how phages should be selected, tested, manufactured, administered and monitored, as well as laboratory infrastructure, quality control, treatment documentation and priorities for future research.

Until now, doctors and researchers have lacked a unified international framework for many of the essential procedures and quality standards involved in using phages as medical treatments. Antibiotic resistance is making bacterial infections increasingly difficult to treat around the world, and bacteriophages — viruses that naturally infect and can destroy bacteria — are one possible alternative. Unlike many antibiotics, which can act against a broad range of bacteria, phages typically target particular bacterial species or even individual strains.

Research so far suggests that properly manufactured and administered phages generally have a favorable safety profile. However, controlled clinical trials have not yet provided sufficient evidence to establish how reliably the treatment works. For that reason, the new guidelines do not recommend phage therapy as a routine treatment for bacterial infections, and instead emphasize carefully evaluating individual patients and using the approach only when circumstances justify it.

Early clinical experiences suggest phage therapy could benefit some patients with difficult infections. In a Belgian case series involving 100 people who received phage treatment, 77 percent experienced an improvement in their clinical condition, and in 61 percent of cases tests could no longer detect the bacteria the treatment had targeted. Observational studies cannot establish whether phages were responsible for the improvements or determine how well the treatment would perform in a controlled trial, so larger, carefully designed studies will be needed.

A central challenge is finding the correct virus for each patient. Because phages are highly selective, laboratories must test whether a candidate virus can kill the specific bacterial strain involved, a process known as a “phage match” that should be completed as quickly as possible before treatment begins. The guidelines recommend that treatment decisions involve a team of specialists, including the patient’s physicians, clinical microbiologists and recognized phage experts, and set expectations for cooperation among laboratories, manufacturing facilities, pharmacies and clinical teams. They also call for cases to be systematically documented and entered into registries.

“The standardization of quality criteria for the production of phages for personalized use, as well as the identification of infrastructural requirements, are essential components of the guideline and important prerequisites for reliable treatments,” says Dr. Annika Claßen.

Claßen, a researcher with the German Center for Infection Research (DZIF), played a leading role in developing the recommendations and directs the “Translational Bacteriophage Research Group” at University Hospital Cologne. Other major contributors include PD Dr. Silvia Würstle, Prof. Maria Vehreschild and Dr. Simone Lieberknecht-Jouy of Goethe University Frankfurt.

“The guideline provides physicians, pharmacists, and regulatory authorities with a common framework for safely and responsibly incorporating phage therapy into clinical practice,” says PD Dr. Würstle, the corresponding author of the guideline.

At Frankfurt University Medical Center, Würstle is overseeing the development of facilities and procedures to provide phage therapy in line with the new recommendations. The medical center reports that ten patients have been successfully treated through its guideline-based phage therapy program since February 2026, using viruses individually selected to target the bacteria causing each patient’s infection. Among the pathogens treated are Pseudomonas aeruginosa and Staphylococcus aureus. Phages may be delivered intravenously, by inhalation, as a nasal spray or through a sterile hydrogel, depending on the infection and the patient’s needs.

The guidelines highlight PhageNET DZIF, a network established and coordinated by Claßen, as an important platform for exchanging scientific knowledge and clinical experience. The recommendations were developed through a structured consensus process under the AWMF (Association of the Scientific Medical Societies in Germany). They are valid from January 5, 2026, through June 29, 2030, with the responsible committee reviewing them annually to determine whether updates are needed.