The German Center for Infection Research (DZIF) reports on a new international guideline for personalized phage therapy. The guideline was developed by an international working group led by the German Society for Infectious Diseases (DGI). Two DZL Principal Investigators, Prof. Dr. Martin Witzenrath and Prof. Dr. Matthias Pletz, were also involved in its development.
The guideline was developed with the participation of 20 scientific and medical societies, 18 international experts, including representatives of regulatory authorities, and two patient advocacy organizations. It comprises more than 60 practical recommendations covering, among other areas, the selection and testing of suitable phages, infrastructure, manufacturing and quality control, application, monitoring and documentation, as well as future research priorities. The consensus statement was published in the journal Nature Medicine on September 21, 2026.
The guideline provides the first internationally agreed framework for the clinical use of personalized phage therapies. Until now, there have been no standardized recommendations for key steps in treatment or quality standards for the use of phages as therapeutic agents.
Antibiotic-resistant bacteria are making infections increasingly difficult to treat worldwide. Bacteriophages, or phages for short, are viruses that specifically infect and kill bacteria. Unlike many antibiotics, they generally target only certain bacterial species or individual strains. Before treatment, it must therefore be determined whether a suitable phage is effective against the pathogen concerned.
Personalized phage therapy may be considered particularly when established treatment options are ineffective, unavailable, or unsuitable. Clinical research to date indicates a favorable safety profile when phages are manufactured and administered according to appropriate quality standards. However, their efficacy has not yet been sufficiently demonstrated in controlled clinical trials. The new guideline therefore considers phage therapy an individually assessed treatment option rather than an established standard treatment.
Observational data provide initial indications of possible treatment success. In a Belgian case series of 100 treated patients, the clinical condition improved in 77% of cases, while the bacteria targeted by the treatment were no longer detectable in 61%. However, such data cannot replace controlled clinical trials.
Because phages are highly specific to their bacterial hosts, a suitable phage must be identified for each individual case, and its activity against the patient's current bacterial strain must be tested. The guideline recommends that each case be assessed by an interdisciplinary team involving the treating physicians, clinical microbiology specialists, and phage experts.
Before treatment begins, testing should be performed as soon as possible to determine whether the phage is effective against the current bacterial strain – a process known as phage matching. This is important because bacterial susceptibility to phages can change over the course of an infection. In infections involving multiple pathogens, all relevant bacteria should be tested.
Two DZL Principal Investigators, Prof. Dr. Martin Witzenrath (Charité – Universitätsmedizin Berlin) and Prof. Dr. Matthias Pletz (Jena University Hospital / Friedrich Schiller University Jena), also contributed to the development of the guideline. Witzenrath additionally serves as Scientific Coordinator of the DZL Disease Area Pneumonia and Acute Lung Injury (PALI).
The guideline also addresses collaboration between laboratories, phage manufacturing facilities, pharmacies, and clinical teams. Standardized testing procedures and regular proficiency testing are intended to improve the quality and comparability of results. Treatment cases should also be systematically documented and entered into registries to evaluate clinical experience and identify open research questions.
“The guideline provides physicians, pharmacies, and regulatory authorities with a common basis for integrating phage therapy into clinical practice safely and responsibly,” says PD Dr. Silvia Würstle, corresponding author of the guideline. At University Hospital Frankfurt, she is responsible for establishing the infrastructure required for guideline-compliant phage therapy.
The work at University Hospital Frankfurt demonstrates what implementation in clinical practice can look like: Since February 2026, ten patients have been treated there with guideline-compliant phage therapy. Individually selected phages have been used against pathogens including Pseudomonas aeruginosa and Staphylococcus aureus. Depending on the clinical situation, phages can be administered intravenously, by inhalation, or as a nasal spray. Application as a sterile hydrogel is also possible.
The guideline also highlights PhageNET DZIF, a network established and coordinated by Dr. Annika Claßen, as a platform for scientific and clinical exchange on phage therapy. The guideline brings together expertise from microbiology, clinical medicine, pharmacy, manufacturing, and regulatory affairs. It is intended to help healthcare professionals better assess the requirements and limitations of individualized phage treatment.
The guideline was developed through a consensus-based process within the framework of the Association of the Scientific Medical Societies in Germany (AWMF). It is valid from January 5, 2026, through June 29, 2030. The responsible committee will review annually whether an update is required.
