An Oklahoma pharmacy has agreed not to provide the state of Missouri with an unofficial, improvised drug for an inmate’s execution scheduled for later this month, according to court documents filed on Monday.

The Apothecary Shoppe of Tulsa will not prepare or provide pentobarbital or any other drug for use in Michael Taylor’s execution, the papers say. The documents ask a judge to dismiss the case that Taylor’s lawyers had filed against the pharmacy seeking to stop it from providing the execution drug. A hearing is scheduled for Tuesday.

Taylor’s lawyer, Matt Hellman, said that as part of the deal the pharmacy acknowledged it had not already provided any drug to the Missouri department of corrections for the execution, which is scheduled for 26 February.

The department and the state attorney general’s office did not immediately return calls on Monday night seeking comment about the agreement or the status of Taylor’s execution.

The Missouri governor, Jay Nixon, suggested last week that the state has drugs to carry out Taylor’s execution. Nixon, speaking at a news conference on Thursday, did not directly answer yes or no when asked, but said: “In order to complete that ultimate responsibility, that’s necessary. The department of corrections is prepared to carry out that execution.”

Taylor pleaded guilty to abducting, raping and stabbing to death a 15-year-old Kansas City girl in 1989.

The Apothecary Shoppe has not acknowledged that it supplies a compounded version of pentobarbital to Missouri for use in lethal injections, as Taylor says, and says it can’t because of a Missouri law requiring the identities of those on the state’s execution team to be kept confidential.

In his lawsuit Taylor alleged that Missouri turned to the Apothecary Shoppe to supply compounded pentobarbital because the only licensed manufacturer of the drug refuses to provide it for lethal injections. That company, Illinois-based Akorn Inc, agreed to that condition when it bought the exclusive rights to the drug in January 2012 from a Danish company that had produced it under the trade name Nembutal.

Taylor contends that several recent executions in which compounded pentobarbital was used showed it would likely cause him “severe, unnecessary, lingering and ultimately inhumane pain”.

Within 20 seconds of receiving his lethal injection on Jan. 9 at the Oklahoma State Penitentiary, 38-year-old Michael Lee Wilson said: “I feel my whole body burning.” This statement described “a sensation consistent with receipt of contaminated pentobarbital,” Taylor alleges.

The lawsuit also cites the 15 October 2012, execution in South Dakota of Eric Robert. Robert, 50 cleared his throat, gasped for air and then snored after receiving the lethal injection, which included compounded pentobarbital. His skin turned a purplish hue and his heart continued to beat for 10 minutes after he stopped breathing, the lawsuit contends. It took 20 minutes for authorities to finally declare Robert dead.

Taylor’s lawsuit questions whether the Tulsa pharmacy can legally produce and deliver compounded pentobarbital. It says the pharmacy is not registered as a drug manufacturer with the US Food and Drug Administration and alleges that it violates federal law each time it delivers the drug across state lines to Missouri corrections officials.

The Associated Press contributed to this report

