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Advancing alternatives to horseshoe crab blood

Every year, hundreds of thousands of horseshoe crabs are harvested for their blood, despite the availability of safe and effective alternatives.

Horseshoe crabs are an ancient, ecologically important, and endangered species.

Yet every year, hundreds of thousands are harvested for their blue blood, which is used to test the safety of injectable vaccines and medications. Since 2018, Revive & Restore has advocated for the adoption of the safe, effective and commercially scalable alternatives that are available for endotoxin testing. These alternatives have existed for decades but lagged in adoption due to regulatory hurdles. Together with scientific, legal, and industry partners, we are working to revolutionize endotoxin testing procedures and safeguard this ancient species.

Endangered horseshoe crab being bled in a factory


There is no better example than the horseshoe crab of an opportunity to save a species using appropriate biotechnology. The species is bled for its Limulus amebocyte lysate (LAL), which the pharmaceutical industry uses for safety testing. But there is a more sustainable, more consistent synthetic alternative to LAL—Recombinant factor C (rFC).

We work to promote the adoption of rFC and stop the bleeding of this threatened keystone species, including

  1. Advance the use of rFC equivalency guidelines from the European Pharmacopeia
  2. Urge the US Pharmacopeia and the FDA to catch up with international standards
  3. Highlight the efficacy, safety, and equivalency data of rFC
  4. Raise awareness of the importance of the horseshoe crab and rFC


Pharmacopeia organizations set quality, purity, strength, and identity standards for medicines around the world. The European, Japanese, and Chinese Pharmacopeias all recognize rFC as an equivalent to LAL. On July 1, 2020, the European Pharmacopeia published compendial chapter 2.6.32.stating, “A test for bacterial endotoxins using rFC can be used in the same way as LAL-based methods.”

Unfortunately, USP has not recognized equivalency. While their current guidelines state pharmaceutical manufacturers can use rFC, they require that drug manufacturers prove equivalency between rFC to LAL every time a drug is produced—a burdensome step not supported by the peer-reviewed literature or fundamental biotechnology science.

Despite this, one pharmaceutical giant, Eli Lilly took on that task and is already using rFC. Lilly released their first therapy using rFC in 2018 and its second in June 2020. Moving forward, Lilly intends to use the new European Pharmacopeia equivalency guidance to seek future drug approvals.We urge all drug developers to do the same—use the European Pharmacopeia guidance to seek approval for future therapies and avoid the requirements of USP entirely. As spelled out in our video at right, this is especially important amidst the rush to develop 14 billion coronavirus vaccines.


Until recently, USP was expected to deliver rFC equivalency guidelines. But with an announcement on May 29, 2020, USP went back on their earlier decision to do so. Now, USP says they will develop an entirely separate chapter for rFC—a process that is likely to take years.

Since the May 29 announcement, Revive & Restore has led the charge to demand USP reverse its decision. Letters from Revive & Restore, Eli Lilly, Pfizer, The Physicians Committee for Responsible Medicine, the Audubon Society of New Jersey, and the Horseshoe Crab Recovery Coalition have been sent to USP for comment.

We urge USP to do what they said they were going to do: 1) honor the existing science and data and stop demanding further studies, and 2) do what is necessary so that pharmaceutical companies can more readily adopt rFC.


To date, the synthetic alternative rFC has been studied in the development of 213 pharmaceutical products in 8 categories, providing significant efficacy, equivalency, and safety data in vaccines, raw materials, and large- and small-molecule drug products.

Our own 2018 review article published in PLOS Biology demonstrated that commercially available rFC tests detect endotoxins with results equivalent to or better than LAL, regardless of which company manufactured it. The study also found that:

  • rFC is just as efficacious and safe as LAL.
  • rFC is more consistent than LAL.
  • rFC causes fewer false positives than LAL and is more cost-effective.
  • rFC is more widely available than ever.
  • rFC for testing of injectable medications is allowed by the FDA.
  • rFC can reduce the need to use horseshoe crab blood by 90%.


“The world currently relies on a single source of lysate, the horseshoe crab family, and more specifically, two species of the crab, Limulus polyphemus and Tachypleus tridentatus (both of which are known to be endangered). The publication of the new general chapter 2.6.32 therefore marks a significant step towards alleviating the need for these animal resources.”—The European Directorate for the Quality of Medicines, July 01, 2020


In 2018, Revive & Restore hosted a press event in Cape May, New Jersey, a location renowned for its concentrations of shorebirds and breeding horseshoe crabs. The event was joined by the state’s First Lady Tammy Murphy, the New Jersey Audubon Society, and representatives of Eli Lilly to announce research findings that dispel the barriers to adopting the synthetic alternative, rFC.

This event led to a wide array of much-needed media coverage of the horseshoe crab and rFC. It also led to several environmental groups joining forces for the horseshoe crab. Now, several Atlantic Coast state Audubon societies, the National Wildlife Federation, the National Resource Defense Council, Eli Lilly, the American Bird Conservancy, Revive & Restore, and other organizations make up the Horseshoe Crab Recovery Coalition. This group is leading a science-based campaign that aims to stem years of decline in horseshoe crab populations and fully restore them by 2030.