Judge rejects claim from 33 death row inmates and says they did not prove the one-drug method led to a painful and lingering death

A judge in Tennessee has upheld the state’s lethal injection process for executing inmates, hours after a federal judge in Mississippi said that state’s process may break the law.

At issue in both cases is the efficacy of the states’ execution drugs. US states have been experimenting with various combinations of lethal injection since a European-led boycott made it difficult to obtain the drugs they require to carry out executions.

Tennessee uses a single drug, pentobarbital, to execute its inmates; Mississippi relies on a three-drug mixture including a pentobarbital or midazolam, sedatives that are followed by a paralysing agent and a drug that stops an inmate’s heart.

In Tennessee, Davidson county chancery judge Claudia Bonnyman said from the bench that the plaintiffs, 33 death row inmates, did not prove that the one-drug method led to a painful and lingering death.

She also said the plaintiffs did not show during a lengthy trial that there had been problems in states where the method was used.

“Plaintiffs were not able to carry their burdens … on any of their claims,” Bonnyman said.

She also said the plaintiffs did not show during a lengthy trial that there had been problems in states where the method was used.

“Plaintiffs were not able to carry their burdens … on any of their claims,” Bonnyman said.

In Mississippi, meanwhile, US district judge Henry T Wingate said Mississippi’s plans did not appear to include a drug meeting the legal requirement for an “ultra short-acting barbiturate” that would render a person unconscious almost immediately.

Three death row prisoners sued, saying they could remain conscious during execution. During the lawsuit, Mississippi changed its procedure to say it would use midazolam as a sedative, after the US supreme court approved the drug’s use in Oklahoma.

Mississippi officials have said they struggle to buy pentobarbital because death penalty opponents had pressured manufacturers to cut off the supply.

Midazolam has been implicated in troubled executions in Arizona, Ohio and Oklahoma that went on longer than expected as inmates gasped and made other sounds.

The US supreme court ruled five to four in June that Oklahoma’s use of midazolam in executions did not violate the eighth amendment prohibition on cruel and unusual punishment.