MIAMI (AFP) - The state of Florida on Thursday (Aug 24) is set to execute its first death row inmate in nearly two years, using a lethal injection drug that has not yet been used in the United States.

The execution of Mark Asay is scheduled for 6pm local time (6am on Friday Singapore time).

The 53-year-old white inmate was sentenced to death in 1988 in the racially motivated double murder a year earlier of a black man, Robert Lee Booker and Robert McDowell in Jacksonville, Florida, who has been identified as white and Hispanic.

Asay would be the first prisoner to be executed in the state since January 2016, before the state's supreme court ruled that Florida executions were unconstitutional because judges were granted powers that should be reserved for juries.

A Florida Supreme Court earlier this month denied Asay a stay of execution. Asay had challenged the state's use of the drug etomidate, a sedative that has not been used before in US executions.

It will replace another controversial drug midazolam, the subject of significant legal wrangling.

According to critics, it does not always adequately sedate prisoners who can therefore be subjected to excessive suffering.

In her dissent to the court's ruling, Justice Barbara Pariente said the state has treated Asay "as the proverbial guinea pig of its newest lethal injection protocol."

Ashley Cook, a spokeswoman for the Florida Department of Corrections, told AFP the department "follows the law and carries out the sentence of the court."

"This is the department's most solemn duty and the foremost objective of the lethal injection procedure is a humane and dignified process."

Janssen, a pharmaceutical division of the company Johnson & Johnson, developed etomidate and has objected to its use in the lethal injection drug cocktail.

"Janssen discovers and develops medical innovations to save and enhance lives," spokesman Greg Panico told the Washington Post.

"We do not condone the use of our medicines in lethal injections for capital punishment."

Asay would be the first white man convicted of killing a black man executed in the state since Florida reinstated the death penalty in 1976, according to the Death Penalty Information Centre. Since then the state has executed 92 inmates.

Asay fatally shot Booker, an African American, after making racist remarks, according to prosecutors.

He killed his other victim, McDowell, who was apparently dressed as a woman, after making a deal to pay him for sex.