Law firm Sidley Austin has filed a lawsuit against the US Food and Drug Administration (FDA) on behalf of six death-row prisoners, seeking to prohibit the agency from importing or using unapproved sodium thiopental.

According to the lawsuit, the FDA has knowingly allowed sodium thiopental, which it has not approved, to be imported by state correction agencies for use in executions by lethal injection.

The FDA is required to prohibit the importation of any drug that is unapproved, misbranded, or adulterate. However, sodium thiopental was recently imported in three states for use in lethal injections.

The lawsuit has asked the federal district court in Washington DC to declare that FDA has violated federal law.

It adds that the court should prohibit the agency from allowing further importation of unapproved sodium thiopental into the US, and take steps to destroy any unlawful, unapproved product previously used.

Bradford Berenson, a partner in Sidley Austin’s Washington office, said that the lawsuit is not about halting executions but rather about ensuring that illegal drugs are not used in carrying out otherwise lawful sentences.

“Ineffective anaesthesia that subjects condemned prisoners to needless, and indeed unconstitutional, suffering serves no one’s interests, least of all the states,” Berenson added.