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What is Phage Therapy?

Phage therapy is a type of antimicrobial therapy that uses bacteriophages (viruses that target bacteria) to treat acute or chronic bacterial infections. It can be administered to patients via multiple routes including oral, topical and intravenous administration.

Phages can be manufactured as ‘off-the-shelf’ products, with a standardised formulation. Alternatively, it can also be used as a personalised medicine, individually tailored to target and treat the specific bacterial strain(s) responsible for a patient’s infection.

This therapy has been used to treat bacterial infections for over a century, first applied in 1919 to cure cases of dysentery. However, when antibiotics like penicillin were discovered in the 1920s, interest in phage therapy amongst the scientific and medical community declined. With the emerging threat posed by the antimicrobial resistance (AMR) crisis, interest in phage therapy has grown.

77.2%

Of patients in a 100-case study showed clinical improvement when receiving last-resort phage therapy in combination with antibiotics.1

61.3%

Eradication rate of target bacteria in the same study.1

Benefits of phage therapy

  1. 1

    Kills antibiotic-resistant strains

    Because phages use completely different physiological mechanisms to infect and kill bacteria, they remain highly effective against multi-drug resistant strains.2

  2. 2

    Ultra-specific host ranges

    Phages only bind to a specific bacterial host species or strain. Unlike broad-spectrum antibiotics, they do not disrupt the protective gut microbiome.2

  3. 3

    Works to improve antibiotics

    Phage-antibiotic combination therapy can force bacteria into evolutionary trade-offs, sometimes resensitizing them to standard chemical antibiotic agents.3

  4. 4

    Degrades biofilms

    Biofilms are complex communities of microorganisms surrounded in a glue-like matrix. These microbial communities have been found to be up to 1000 times more resistant against antibiotics, compared to free-living bacteria4 and are responsible for chronic infections. Molecules known as enzymes, produced by phages, can breakdown and degrade biofilms, making these complex microbial communities more susceptible to antibiotic treatment.5

Regulatory landscape in the UK

In 2024, the UK Government formally acknowledged the clinical potential of bacteriophages in addressing the antibiotic resistance crisis.6 Subsequently, the Medicines & Healthcare products Regulatory Agency (MHRA) released guidance documents establishing that any phage used to prevent or treat disease in the UK is classified as a medicinal product7. Phage therapies can be formulated from natural or engineered phages. Natural phages are isolated from environmental sources, such as rivers or the human body, and remain genetically unmodified. Engineered phages can be artificially produced in a lab or can be derived from natural phages which have subsequently undergone genetic modification. Phages may be genetically modified to enhance the therapies mode of action or enhance the stability of the formulation.

Phage preparations can fall into three distinct classes in the UK8

  • Natural Phages: Genetically unmodified agents isolated from environmental sources. Classified as biological medicinal products.
  • Engineered Phages (Passive): Artificially produced phages that do not directly alter the mode of action. Classified as biological medicinal products with Genetically Modified Microorganism (GMM) status.
  • Engineered Phages (Active Mode): Phages edited to actively modify therapeutic effect. Classified as gene therapy medicinal products (and GMM).

Currently, phage therapy is available in the UK strictly on a compassionate use basis as an unlicensed medicine, reserved for patients who have exhausted all standard antibiotic options.

References

(1) Pirnay, J-P. Djebara, S. Steurs, G. Griselain, J. Cochez, C. De Soir, S et al. Nature Microbiology 2024. Personalised bacteriophage therapy outcomes for 100 consecutive cases: a multicentre, multinational, retrospective observational study.

(2) Olawade, DB. Fapohunda, O. Egbon, E. Ebiesuwa, OA. Usman, SO. Faronbi, AO et al. Microbial pathogenesis 2024. Phage therapy: A targeted approach to overcoming antibiotic resistance.

(3) Chan, BK. Sistrom, M. Wertz, JE. Kortright, KE. Narayan, D. Turner, PE. Scientific Reports 2016. Phage selection restores antibiotic sensitivity in MDR Pseudomonas auerginosa.

(4) Sharma, D. Misba, L. Khan, AU. Antimicrobial Resistance & Infection Control 2019. Antibiotics versus biofilm: an emerging battleground in microbial communities.

(5) Lu, TK. Collins, JJ. PNAS 2007. Dispersing biofilms with engineered enzymatic bacteriophage.

(6) House of Commons. 2024. The antimicrobial potential of bacteriophages.

(7) HM Government. 2024. Confronting antimicrobial resistance 2024 to 2029.

(8) Medicines & Healthcare products Regulatory Agency. 2025. Regulatory considerations for therapeutic use of bacteriophages in the UK.