The Janssen unit of Johnson & Johnson has hit out at plans by the US state of Florida to execute a death row prisoner using an experimental lethal injection that contains an active ingredient the company developed in the 1960s.

J&J no longer manufactures the off-patent etomidate, a short-acting sedative, but several other US drugmakers do. In a statement, the US healthcare giant said it is speaking out for the first time against the use of its medicines for capital punishment – which it does not condone – as it would be the first time one has been used for this purpose.

Florida has not disclosed which drugmaker manufactures the generic. According to a US government database of prescription drugs cited by British newspaper Financial Times, both Pfizer and and Mylan have etomidate in their portfolio.

Barring a last-minute reprieve, 53-year-old Mark James Asay, convicted for murdering two men, was due to be executed on Aug. 24 with a three-drug “protocol” that  includes etomidate as a substitute for the more powerful midazolam.

The other two drugs in the so-called “cocktail” are the muscle relaxant rocuronium bromide, and potassium acetate, which is said to stop the heart when administered in high enough doses. The latter was selected as a substitute for potassium chloride, which is harder to secure because of the supply controls.

Reports said potassium acetate has been used in a lethal injection only once, by mistake – in a 2015 execution in Arkansas that was generally regarded as botched. The attention this case received led to public outcry and led to the use of different formulations in subsequent executions.

Lawyers for Asay had argued that introducing etomidate into the protocol violated the US constitution as its use for the purpose was untried. The Florida Supreme Court rejected this argument, ruling on Aug. 15 that the execution to could go ahead. A dissenting judge said the inmate, one of 362 currently on the state’s death row, had not been given time to procure the documents needed to challenge the use of the drug.

Legal experts opposed to capital punishment said it was worrying that Florida courts are allowing the execution to proceed without requiring the state Department of Corrections to produce key information about the safety and efficacy of the new lethal injection protocol and drugs.

A physician commenting on the case said etomidate is fairly short-acting, so there is a risk that its effects could wear off during the execution process. Also, as the drug is dissolved in an organic solvent, it can make veins very painful during and after injection.

Like other death penalty states, Florida has had difficulty obtaining execution drugs, as many US pharmaceutical companies include clauses in distribution contracts barring the use of their medications for this purpose. To ease procurement, some states have passed legislation allowing suppliers to remain anonymous. The EU prohibits exports of drugs that could be used in lethal injections.

It is not clear how Florida circumvented the drugmakers’ restrictions. Some speculate that the state could have amassed supplies of etomidate, which for the most part is used during surgery, before it publicly announced its intention to use it in a lethal injection earlier this year.