The US state of Oklahoma has carried out its first execution since a botched lethal injection left a death row inmate writhing in agony in April.

Prison officials declared Charles Frederick Warner (47) dead at 7:28pm on Thursday night.

He was on death row for killing his roommate's baby in 1997 and had appealed to the US Supreme Court to halt his execution on the grounds it presented an unconstitutional risk of pain and suffering.

It was the second time Oklahoma used the surgical sedative midazolam as part of a three-drug method.

Warner was originally scheduled to be executed in April last year, on the same night as Clayton Lockett, who began writhing on the gurney and trying to lift his head after he had been declared unconscious.

Attorneys for the state of Oklahoma said the problems with Lockett's execution were caused by a failed intravenous line and a lack of training, rather than the drugs used.

Justice Sonia Sotomayor referred Warner's request, along with three other Oklahoma death row inmates, to the Supreme Court, which voted 5-4 against a stay of execution.

Oklahoma has increased its midazolam dosage to five times the amount. On Thursday night, Florida also executed a death row inmate using the same procedure.

Johnny Shane Kormondy, who was convicted as the ringleader of a 1993 home-invasion robbery with ended in the murder of a banker and the rape of his wife, was pronounced dead at 8:16pm at Florida State Prison.

His execution was delayed by two hours by the US Supreme Court appeal, which was eventually denied.