McALESTER, Okla. - Oklahoma officials executed a murderer Thursday using a drug combination that included a sedative commonly used to euthanize animals, after a nationwide shortage of a key ingredient forced the state to alter the usual formula.

John David Duty was pronounced dead at 6:18 p.m. at Oklahoma State Penitentiary.

The 58-year-old, sentenced to die for strangling his cellmate nearly a decade ago, is believed to be the first person in the United States whose execution included the use of pentobarbital.

Duty and two other death-row inmates had challenged the state's decision to use pentobarbital, arguing it could be inhumane because a person can be paralyzed but still aware when a painful third drug is administered to stop the heart.

On Tuesday, a federal appeals court upheld a ruling against the two other inmates. Duty did not take part in the appeal.

Several states have been scrambling since Hospira Inc. - the only U.S. manufacturer of sodium thiopental, the barbiturate normally used in executions - said new batches of the substance would be available only "in the first quarter" of next year.

Oklahoma obtained a dose from Arkansas for its last execution, in October, but could not secure more, said Department of Corrections spokesman Jerry Massie.

Executions have been delayed in California, Arkansas, Tennessee, and Maryland as a result of protocol changes, including the use of new drugs, said Richard Dieter, executive director of the Death Penalty Information Center.

Oklahoma's law calls for the use of a fast-acting barbiturate to be administered first, which gave the state the flexibility to use pentobarbital, Massie said.

"I think Oklahoma is the only state where this issue has come to a head over a new drug," Dieter said. "The other states that haven't been able to do it, it's because the state courts wanted more time to review the overall protocol changes."