Interpretation guidance for MHRA regulatory considerations for phage therapeutic products

On 4 June 2025, MHRA published its first comprehensive guidance for the therapeutic use of bacteriophages in the UK — “Regulatory considerations for therapeutic use of bacteriophages in the UK.” In response, the authors of this article produced an “interpretation guidance” to translate the regulatory document into accessible language for academic researchers and small- to medium-sized enterprises (SMEs) developing phage therapeutic products (PTPs).

They clarify how phage therapies are regulated — either as licensed medicines, investigational products, or under “specials” (unlicensed but medically justified use) or import regimes. The guidance emphasises that many phage therapies will be classified as biological medicines; genetically modified phages may even be considered as gene-therapy/advanced therapy medicinal products (ATMPs), with additional environmental-release or containment regulations.

Beyond regulatory classification, the article outlines the key expectations for quality, safety, and efficacy evidence across the product lifecycle. For instance:

• Quality: developers must thoroughly characterise the phage product (identity, purity, activity), control batch-to-batch variability, and comply with good laboratory/manufacturing practices.
• Safety: preclinical safety testing should be justified and proportionate; regulators encourage minimizing animal use and instead relying on well-controlled in vitro or other relevant assays where feasible.
• Efficacy: potency assays must be defined and reproducible; as the field evolves, demonstrating consistent bactericidal or bacteriostatic activity under defined conditions will be required.

The paper also draws attention to regulatory-environmental overlap: engineered phages may trigger environmental risk assessments if they qualify as genetically modified organisms (GMOs), which involves additional scrutiny (e.g., containment, release permits).

Importantly, the authors embed multiple practical examples throughout — to help developers understand what kind of data/documentation regulators expect when submitting a marketing-authorization application (MAA) or applying for unlicensed use.

In short: this article transforms the dense regulatory text from MHRA into developer-friendly guidance, clearly mapping out how phage therapies can — and should — be developed under UK law, what classification they’ll fall under, and what quality, safety and efficacy data will be needed for eventual clinical use.

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