The US Federal Drug Administration (FDA) has issued a warning against the use of bulk drug substance caesium chloride on the same day that non-profit group Public Citizen filed a lawsuit to compel the agency to restrict the compound.

The agency said on 23 July that it had issued “compounding risk alert” to healthcare providers, compounders and patients of the dangers of using caesium chloride, which is sometimes used by cancer patients “despite never having been proven safe and effective for any use”.

Additionally, the FDA said it would move the compound to category two under its interim policy on compounding with bulk drug substances, meaning it posed “significant safety risks” to patients, and the agency would take regulatory action against any compounders caught using it.

Public Citizen previously filed a petition with the FDA in 2017 calling for caesium chloride to be added to the list of category two compounds and banned in pharmacy compounding due to “serious health risks”.

In a lawsuit filed on 23 July in the United States District Court for the District of Columbia, Public Citizen asked the court to “compel” the FDA to act on the petition. The non-profit sought a declaration – to “protect public safety” and “forestall preventable death and injury” – that the FDA had “acted unlawfully” by “withholding action” in the matter.

Later the same day, the FDA issued a response granting the request to re-categorise the compound. The agency said that it could not add caesium chloride to the “503a bulks list”, thereby effectively banning it from use in compounding, as it is currently engaged in rulemaking to establish the list and had not yet considered whether the compound would be included.

It noted that once it had proposed a rule “addressing caesium chloride”, the public – including Public Citizen – would be able to comment on its potential addition to the bulks list.

Sidney Wolfe, founder and senior adviser of Public Citizen’s health research group, said that while the organisation supported the FDA’s “belated action”, the agency should have acted when its own reviewers concluded the compound was “not safe for human use” over two years ago.

“By not acting more expeditiously, the agency has allowed consumers to continue to be exposed to a dangerous and ineffective medication that has been promoted without basis to vulnerable cancer patients,” he added.

“The FDA seeks to implement the statutory requirements for bulk drug substances that can be used in compounding in a way that strikes a balance between preserving access to compounded drugs for patients who have a medical need for them while reducing the safety risks and protecting the FDA drug approval process,” FDA deputy commissioner Anna Abram said in the agency’s announcement.

“Input from stakeholders, including healthcare professionals, is critical to achieving this balance,” she added.

In the United States District Court for the District of Columbia

Public Citizen Inc v Food and Drug Administration

  • Judge Tanya Chutkan

Counsel to Public Citizen

Public Citizen Litigation Group counsel Rebecca Smullin