St. Christopher's Hospital for Children, acquired in January by American Academic Health System, is laying off 45 people and eliminating an unspecified number of positions in its physician practices, according to a letter sent to employees Tuesday by interim chief executive George Rizzuto.

The cuts amount to about 7 percent of the workforce in the North Philadelphia hospital's practices, spokeswoman Gabrielle Lacherza said. Those being laid off were given severance or offered positions at other American Academic Health System facilities, she said.

American Academic, a unit of California private equity firm Paladin Capital, bought St. Christopher's and Hahnemann University Hospital from Tenet Healthcare Corp. for $170 million.

Rizzuto said in his letter that American Academic was considering the expansion of certain pediatric services to Hahnemann and bringing some adult services to St. Christopher's.