A death row inmate who was executed by the state of Ohio on Thursday with an untried and untested combination of two medical drugs appeared to gasp and snort in a procedure that took an unusually long 25 minutes to kill him.

Dennis McGuire was pronounced dead at 10.53am at the Southern Ohio Correctional facility in Lucasville. His lawyers had warned ahead of the proceeding that the experimental combination of the sedative midazolam and painkiller hydromorphone might subject him to “air hunger”, an insufficient flow of air into the lungs causing the sensation of suffocation.

In court proceedings last week, an Ohio state prosecutor said bluntly: “You're not entitled to a pain-free execution,” and a judge allowed the execution to proceed.

A reporter for the Associated Press, which sends a journalist to every execution in the US, wrote that McGuire “appeared to gasp several times during his prolonged execution ... McGuire made several loud snorting or snoring sounds during the more than 15 minutes it appeared to take him to die. It was one of the longest executions since Ohio resumed capital punishment in 1999. McGuire's stomach rose and fell several times as he repeatedly opened and shut his mouth.”

Another eye-witness report from the Columbus Dispatch provided concurring evidence. Dispatch reporter Alan Johnson wrote that four minutes into the procedure, "McGuire started struggling and gasping loudly for air, making snorting and choking sounds which lasted for at least 10 minutes. His chest heaved and his left fist clinched as deep, snorting sounds emanated from his mouth."

Ohio's department of corrections originally put the official length of the execution at 15 minutes, but later in the day revised that to 25 minutes.

McGuire's defence attorney, Allen Bohnert, said that according to reports he had been given from witnesses in the chamber, the prisoner was gasping for breath from about 10.30am to 10.44am. At some point, witnesses told Bohnert, McGuire tried to sit up, turned his head toward his family members who were witnessing, and spoke to them. One witness described the scene as "ghastly".

Bohnert told the Guardian: “At this point, it is entirely premature to consider this execution protocol to be anything other than a failed, agonizing experiment by the state of Ohio. The people of the state of Ohio should be appalled at what was done here today in all of our names.”

McGuire, 53, was executed for the 1989 rape and murder of Joy Stewart, who was 22 and about 30-weeks pregnant at the time. Her unborn child also died.

Members of Stewart’s family were present at his execution, and before it they put out a statement that said the manner in which McGuire was put to death was more humane than the brutal way he had murdered Joy.

Ohio’s recourse to the midazolam-hydromorphone combination was forced by a shortage of pentobarbital, a drug originally manufactured in Denmark, which has been subjected to strict export licences that prevent sale to US departments of correction. A European-wide boycott, designed to ensure that medical drugs are not used to kill people, has begun to bite across the 32 states that still have the death penalty on their books.

Ohio ran out of pentobarbital in September.

The adoption of midazolam as an alternative drug - not only in Ohio, but also in Florida, one of the most active death penalty states – has led to expressions of anger and disgust by leading physicians in the US. Joel Zivot, the medical director of the cardio-thoracic and vascular intensive care unit at Emory University School of Medicine in Atlanta and an opponent of the use of anesthetics in lethal injections, called the use of midazolam in executions “appalling and unethical”, and said, “The public should be concerned that [the] medicines that are used to help them are being diverted instead to kill people.”

The human rights group Reprieve, which has been a key influence behind the European boycott, has accused Ohio and Florida of stockpiling midazolam to the detriment of medical services.

Midazolam, a drug that is commonly prescribed to treat critically-ill patients because of its short half-life and relatively few side-effects, is already in short supply in hospitals, and medical practitioners fear the dearth will now intensify given the sharply increasing demands of prison wardens. The American Society of Health-System Pharmacists, which monitors the supply of pharmaceuticals, reports “demand exceeding supply due to current market conditions”.

Florida, which now uses midazolam in its three-drug lethal injections, injects a dose of 500mg into prisoners. Zivot pointed out that a normal dose for a critically-ill patient would be 5mg. “Do the math – you can see how many patients have been deprived of these medications because of their use in just one execution.”