FDA confirms Animal Rule and PRV potential for Galidesivir in Marburg

• FDA agrees Animal Rule pathway and Priority Review Voucher eligibility for Galidesivir in Marburg virus
• News significantly de-risks the Galidesivir regulatory pathway, with Island’s share price up about 30%
• Priority Review Vouchers have historically commanded prices of up to ~US$155 million on the open market

Special Report: Island Pharmaceuticals is up about 30% today after achieving what it describes as “one of the most important regulatory milestones” in the company’s history.  

The US Food and Drug Administration (FDA) has confirmed that Island Pharmaceuticals’ (ASX:ILA) antiviral candidate Galidesivir, for use against the deadly Marburg virus, is eligible to advance toward approval under the FDA’s Animal Rule.

The Animal Rule is a specialised FDA pathway reserved for life-threatening pathogens where human trials are not feasible or ethical, including filoviruses such as Marburg, which causes severe haemorrhagic fever.

In another major milestone for the antiviral drug development company, the FDA also advised that Galidesivir would qualify for a Tropical Disease Priority Review Voucher (PRV) upon approval under the Animal Rule.

A PRV is one of the most valuable incentives offered by the FDA in drug development, with recent vouchers selling for US$100–155 million on the open market.

Island received written responses on November 12 (US time) to questions posed in a Type C meeting request, with the FDA also providing valuable guidance on Galidesivir’s clinical development program to advance its approval.

The company said it was now focused on incorporating all FDA guidance into Galidesivir’s clinical development program with the initial feedback assisting Island in preparing a study design, set to be finalised alongside discussions with the regulator.

De-risking the Galidesivir program

The FDA’s responses materially de-risk and help accelerate Galidesivir’s development path for use in Marburg.

The Animal Rule allows drugs to be approved based on efficacy demonstrated in well-controlled animal studies when human trials are unethical or not feasible – such as with deadly diseases like Marburg and Ebola.

Galidesivir already has phase I safety data and strong non-human primate (NHP) efficacy data, supporting Island’s strategy that approval can be sought using the Animal Rule framework.

In previously reported NHP studies, Galidesivir achieved an overall 94% survival rate in Marburg-infected primates, compared with 0% in the placebo group.

Island is currently working with its advisors to prepare a series of clarifying questions for the FDA, which may be submitted by December 2.

The company expects that at least one additional non-human primate study will be required, with further requirements to be confirmed through ongoing FDA engagement.

In parallel, Island is liaising with Biosecurity Level 4 (BSL-4) facilities – where Marburg studies can be safely conducted – to brief them on the FDA’s feedback and begin preparations for an updated animal study aligned with the regulator’s guidance.

The company is also finalising a comprehensive development plan incorporating this updated study design, which will be submitted to the FDA for review and approval once complete.

Government stockpile programs present major opportunity

Island said it was also advancing initiatives for Galidesivir’s broader commercialisation in line with its strategy to position the drug as a critical countermeasure against high-priority viral threats for inclusion in government stockpiles.

These initiatives include negotiations with potential trial sites, as well as US Government engagement initiatives.

Island said the US Strategic National Stockpile (SNS) and equivalent programs in allied nations represent a combined multi-US$100m annual procurement opportunity for filovirus countermeasures.

Several antivirals and vaccines have secured multi-year, multi-US$100m SNS contracts. A similar procurement for Galidesivir could provide long-term, predictable revenue streams for the company.

Major regulatory milestone

CEO and managing director Dr David Foster said confirmation that the Animal Rule is a viable path for development of a Marburg countermeasure and that Galidesivir would qualify for a PRV validates the strength of its existing dataset.

He said it highlights the immense opportunity in front of Island and provides a clearly defined, faster path to market.

“These responses from the FDA represent one of the most important regulatory milestones in Island’s history and significantly de-risk the Galidesivir program from a development and commercial standpoint,” he said.

“A Priority Review Voucher alone has the potential to generate substantial strategic and financial value for shareholders, while the Animal Rule pathway enables us to move rapidly towards approval, where traditional trials are not feasible.”

He said the FDA’s detailed guidance on our upcoming clinical development opportunity also provides Island with clarity to advance into the next phase with confidence and it remains on track to work with the regulator to finalise an optimal study design.

Foster said Island was well funded to advance its next phase of development, with $6.9m in cash as at September 30, 2025 and a further $1m expected from in-the-money options due to expire on December 4.

“With strong regulatory momentum, increasing US Government engagement, balance sheet strength and a highly compelling dataset, Island is exceptionally well placed to create meaningful value as we progress Galidesivir towards approval and potential inclusion in national stockpiles,” he said.

This article was developed in collaboration with Island Pharmaceuticals, a Stockhead advertiser at the time of publishing.

This article does not constitute financial product advice. You should consider obtaining independent advice before making any financial decisions.