When a bacterial infection stops responding to every antibiotic on the shelf, physicians have very few options left.
One of them is phage therapy, which uses viruses called bacteriophages to attack and destroy specific bacteria.
Until now, doctors who tried it were largely writing their own protocols case by case.
In September 2026, an international working group led by the German Society for Infectious Diseases published the first standardized clinical guideline for personalized phage therapy in the journal Nature Medicine.
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Twenty professional organizations, 18 international experts and patient advocacy groups contributed to more than 60 practice-oriented recommendations.
What phage therapy actually is
Bacteriophages, or phages, are viruses that infect and kill bacteria.
Each phage is highly specific and only targets certain bacterial strains, so treatment has to be tailored to the individual patient.
A sample of the infection is tested against a library of phages until one matches.
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The chosen phage is then prepared under pharmaceutical quality standards and administered to the patient.
The new document covers phage selection, laboratory testing, manufacturing, quality control, dosing, delivery and follow-up monitoring.
It reserves phage therapy for one specific situation, when established treatments are ineffective, unavailable or unsuitable.
Why it matters now
Antibiotic resistance already fills hospital wards with infections that older drugs cannot touch.
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More than 2.8 million antimicrobial-resistant infections occur in the United States each year, and more than 35,000 people die as a result, according to the CDC.
Globally, bacterial resistance was associated with more than 4.7 million deaths in 2021, and the World Health Organization calls it a major global health threat.
Phages are one of the few alternatives with an early clinical track record.
A multinational case series in Nature Microbiology tracked 100 patients treated with personalized phage therapy for hard-to-treat infections.
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Clinical improvement was reported in 77 percent of cases, and the targeted bacteria became undetectable in 61 percent.
At Frankfurt University Medical Center, ten patients have been treated since February 2026 using individually selected phages.
The phages targeted Pseudomonas aeruginosa and Staphylococcus aureus, two common causes of resistant hospital infections.
Safe so far, but not yet proven
The authors are careful about what phage therapy is today, and what it is not.
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So far, clinical research points to a favorable safety profile when phages are produced and given under proper quality standards.
Controlled trials have not yet shown that the therapy consistently works.
That is why the document treats every case as an individual decision, and asks physicians to log outcomes in registries.
Doctors can then build the evidence base while patients who have run out of antibiotic options still get a chance at treatment.
"The guideline provides physicians, pharmacists, and regulatory authorities with a common framework for safely and responsibly incorporating phage therapy into clinical practice," said PD Dr. Silvia Würstle of Goethe University Frankfurt, the corresponding author.
What happens next
The recommendations are set for annual review and remain in force through June 29, 2030.
Patients with an infection that antibiotics can no longer control should ask their treating physician whether an established phage therapy program is available for their case.
This article is made and published by Mie Hermansen, who may have used AI in the preparation.