The newborn twins of actor Dennis Quaid were among three patients accidentally given 1,000 times the common dosage of a blood thinner, but hospital officials said Tuesday that none of the overdose victims had suffered any ill effects.

Cedars-Sinai Medical Center declined to identify the patients, but a representative for the actor told The Associated Press that they included the two-week-old children of Quaid and wife Kimberly, Thomas Boone and Zoe Grace.

"Dennis and Kimberly appreciate everyone's thoughts and prayers and hope they can maintain their privacy during this difficult time," Quaid's publicist, Cara Tripicchio, said in a statement Tuesday.

The hospital declined to release the patients' conditions Wednesday, citing privacy laws.

The celebrity Web site TMZ.com, which first reported the overdoses, said the children were in stable condition in the neonatal intensive care unit. A Cedars-Sinai official said tests indicated that none of the patients suffered any ill effects from the overdose on Sunday, but apologized to their families.

"I want to extend my deepest apologies to the families who were affected by this situation," Cedars-Sinai's chief medical officer, Michael L. Langberg, said.

The state Department of Public Health is investigating reports of an incident involving newborn twins at the hospital, said agency spokeswoman Suanne Buggy, who declined to elaborate.

Langberg said three patients on Sunday each received vials containing 10,000 units per milliliter of heparin, a blood thinner, instead of vials with a concentration of 10 units per milliliter. The patients were receiving intravenous medications and the heparin was used to flush the catheters to prevent clotting.

Once the hospital staff realized the error, they tested to measure the patients' blood clotting function, Langberg said. One test was normal, but the other two were given another drug, protamine sulfate, that reverses the effects of heparin.

It was not immediately clear which two of the three patients had received the second drug. Further tests on those two "indicated no adverse effects from the higher concentration of heparin," Langberg said. "Doctors continue to monitor the patients."

Protamine sulfate is generally effective in restoring normal clotting function, said Steven Kayser, professor of clinical pharmacy at the University of California, San Francisco.

Heparin, used to treat and prevent blood clots in the veins or arteries, comes in different concentrations and too much can be life-threatening, Kayser said. Overdose symptoms can include nosebleed and bruising.

"Heparin is a good drug, but you have to pay very careful attention because of the varying concentrations," he said.

Last year, three premature infants at an Indiana hospital died after a pharmacy technician mistakenly stocked the medicine cabinet with heparin vials containing a dose 1,000 times stronger than what the babies were supposed to receive. Three others also suffered overdoses but survived.

Quaid and his wife are the biological parents of the twins, who were born Nov. 8 to a surrogate mother.

"God has definitely blessed us," the couple said in a statement announcing their birth.

Quaid, 53, has a 15-year-old son, Jack Henry Quaid, from his marriage to Meg Ryan.

His screen credits include "Great Balls of Fire!" "Any Given Sunday" "The Big Easy" and "Far From Heaven."