HILLSBORO, Mo. (AP) _ A 5-month-old boy whom police believe was poisoned when his mother fed him antifreeze on two occasions died Thursday night, hospital officials said.

Ryan Stallings died about 9 p.m. at Cardinal Glennon Children's Hospital, spokeswoman Laura Sosa said. An autopsy was scheduled for Friday.

His mother, Patricia Stallings, 24, of Hillsboro, is charged with first- degree assault on her son, said Capt. Wally Gansmann of the Jefferson County Sheriff's Department. Further charges were pending, he said.

Gansmann said Stallings' husband was shocked to learn of the allegations. He is not a suspect, Gansmann said.

Authorities believe Stallings may have fed the infant antifreeze as early as July, and again last week by putting it in baby bottles and giving it to the infant during her weekly visit to a foster home where the boy had been living.

Authorities sent Ryan to the foster home in August after suspecting that the boy was fed antifreeze in July.

Gansmann said investigators suspect that the boy was poisoned a second time Aug. 31 during a visit by his mother, but he declined to provide any details.

''We have baby bottles and formula being tested in the laboratory,'' he said. Testing is under way on bottles from both incidents, Gansmann said.

In July, the infant appeared to suffer abdominal pains and was hospitalized for two weeks, Gansmann said. Foul play was suspected and Stallings was charged, he said.

The child then was assigned to the supervision of the state Division of Family Services for six weeks, Gansmann said.

Stallings was allowed to visit the child once weekly at the foster home, where a worker supervised each visit, including the most recent one last Thursday, Gansmann said.

''On Friday, he (Ryan) started having some difficulties, and, by Monday, he was back with the same symptoms as before,'' the captain said. The baby's symptoms included drowsiness, vomiting, nausea and mild convulsions.

Stallings, who is pregnant with her third child, was in custody in Washington County Jail in Potosi.