Oklahoma officials on Friday said the state had obtained manufactured pharmaceuticals from a secret supplier for use in the executions of two men later this month, avoiding concerns over the use of compounded drugs but leaving unanswered questions about how it obtained them.

In a letter to defence lawyers, an assistant attorney general, John Hadden, said the state “has recently acquired a manufactured source of vecuronium bromide. That means there will be no compounded drugs used in the executions of your clients. This will resolve the concerns you and your clients have expressed regarding compounded drugs.”

Despite a judge’s ruling that a state drug secrecy law violated the inmates’ constitutional rights, Hadden declined to identify the supplier of the new drugs.

“This information is irrelevant to your clients and disclosure could lead to harassment or intimidation which will have a chilling effect on the state’s ability to acquire these drugs for future executions,” Hadden wrote.

Oklahoma plans to execute Clayton Lockett on 22 April and Charles Warner on 29 April. Both were convicted of murder and rape.

The state said on Friday it would use midazolam, vecuronium bromide and potassium chloride to kill the men, with dosages untried in US executions. Florida uses the same combination of drugs, but employs a dosage of midazolam, which acts as a sedative, that is five times larger than what Oklahoma plans to use. Vecuronium bromide is a paralytic agent; potassium chloride stops the heart.

Oklahoma had planned to use a different drug – compounded pancuronium bromide – as the second drug in the method, but lawyers objected to the use of loosely regulated compounded drugs that may lack purity and cause an unconstitutionally cruel death.

Hadden said the state will now use drugs that are approved by the Food and Drug Administration.

Madeline Cohen, a lawyer for one of the men due to be executed, said the state needs to reveal details beyond that the pharmaceuticals were manufactured rather than compounded.

“If they disclosed that the drugs were manufactured by a specific company, in a particular lot, and imported with this licence, for example, we would have some ability to evaluate that,” she said.

“Without that, we don’t know if it’s actually an FDA-approved drug or if it has been imported or sold legally, or if it is what the state says it is.”

She said there is no FDA-approved midazolam that comes in the concentration specified in Oklahoma’s lethal injection protocol, and the state has not said if it will dilute the drug to make the concentration.

The state could change the concentrations in the protocol, if any numbers were incorrectly written, Hadden said in his letter.

(the guardian)