Florida has put a man to death with an anaesthetic never used before in a US lethal injection.

Authorities said Mark Asay, 53, the first white man executed in Florida for the killing of a black man, was pronounced dead at 6.22pm local time on Thursday at the state prison in Starke.

Asay received a three-drug injection that began with the anaesthetic etomidate.

Mark AsayMark Asay (Florida Department of Corrections via AP)

Though approved by the Florida Supreme Court, etomidate has been criticised by some as being unproven in an execution.

It replaced midazolam, which became harder to acquire after many drug companies began refusing to provide it for executions.

Asked whether he wanted to make a final statement before his execution, Asay said: “No sir, I do not. Thank you.”

Michelle Glady, a spokeswoman for the corrections department, said there was no complication in the procedure and Asay did not speak during it.

Florida Department of Corrections spokeswoman Michelle Glady addresses reporters after the executionFlorida Department of Corrections spokeswoman Michelle Glady addresses reporters after the execution (AP Photo/Jason Dearen)

The execution was Florida’s first since the US Supreme Court halted the practice in the state after finding its method for sentencing people to death to be unconstitutional.

Earlier that day the court rejected Asay’s final appeal without comment.

Etomidate, the first of three drugs administered in Florida’s new execution mixture, is followed by two others, the last of which stops the heart.

Prison authorities have defended the choice of etomidate, saying it has been reviewed.

Doctors hired by Asay’s lawyers raised questions about etomidate in court declarations, saying there were cases where it had caused pain, along with involuntary writhing in patients.

But in its opinion allowing the drug to be used, the state’s high court said earlier this month that four expert witnesses demonstrated that Asay “is at small risk of mild to moderate pain”.

Prosecutors say Asay made racist comments in the 1987 fatal shooting of a Robert Booker, 34. He was also convicted of the 1987 murder of Robert McDowell, 26, who was mixed race, white and Hispanic.

Asay hired Mr McDowell, who was dressed as a woman, as a prostitute, and killed him after learning his true gender, prosecutors said.

He is the first white man to be executed in Florida for killing a black man.

At least 20 black men have been executed for killing white victims since the state reinstated the death penalty in 1976, according to data from the Death Penalty Information Centre.

A total of 92 Florida inmates had been executed previously in that period.

Cavalry Chapel Prison Ministries Director Norman SmithCavalry Chapel Prison Ministries Director Norman Smith (AP Photo/Jason Dearen)

Asay’s spiritual adviser, Norman Smith of Cavalry Chapel in Melbourne, Florida, who spent two hours with him before his execution, said Asay admitted spouting racial epithets before Mr Booker’s murder, but said he was drunk and angry, not a racist.

“Until I heard that I would’ve never known that this man was tagged as a racist,” said Mr Smith, who is black.