Two premature infants died and a third was in critical condition after being given adult-size doses of medication, prompting hospital officials to review drug-handling procedures.

Adult doses of the blood-thinner Heparin were somehow placed in a drug cabinet at the Newborn Intensive Care Unit of Methodist Hospital, said Sam Odle, chief executive of Methodist and Indiana University Hospitals. The hospital said human error was to blame.

In all, six premature babies were given the adult doses.

Two-day-old Emmery Miller and five-day-old D'myia Alexander Nelson, both girls, died Saturday night, Odle said. Three other infants were in stable condition Monday morning at Methodist, and another who was transferred to Riley Hospital for Children was in critical condition, hospital officials said.

The two girls who died were both born at 25-26 weeks' gestation, Odle said. A full-term pregnancy lasts 38 to 42 weeks.

"These are very, very small babies," Odle said. "We are confident that no other infants except for the six were affected."

Heparin is routinely used in premature infants to prevent blood clots that could clog intravenous drug tubes, but an overdose could cause severe internal bleeding, said Dr. James Lemons, a neonatologist at Riley.

Hospital officials had met with family members, Odle said, adding: "Our hearts go out to the families." But apologies did not satisfy Whitney Alexander, mother of D'myia Nelson.

"They may apologize but it didn't help," she told WTHR-TV. "It didn't help, because I feel like whoever the nurse was on call, they should know what they were doing and how much my baby should have."

The hospital was investigating how the error occurred and reviewing its drug-handling procedures, and some corrective steps had already been taken, Odle said.

"This was human error — that's all," Odle said.

The drug arrives at the hospital in premeasured vials and is placed in a computerized drug cabinet by pharmacy technicians, Odle said.

The adult and infant doses are similarly packaged and somehow the adult doses were placed in the drug cabinet in the newborn unit, Odle said. The hospital will ask the manufacturer to make the packaging more distinct, he said.

Autopsies were to be performed Monday. There was no evidence that infant doses were given to any adult patients, officials said.