(CNN) - South Dakota Sen. Tim Johnson is recovering from gallbladder surgery on Tuesday, his office said in a statement.
"The surgery went exceedingly well," Johnson's doctor, Dr. Donald J. Wingert, said in a statement. "…The Senator is resting comfortably. All of our findings point to the gallbladder as the primary problem, but it is still possible that he is having some lingering effects from the antibiotic drug reaction."
The 63-year-old Democrat was admitted to Avera McKennan Hospital in Sioux Falls, South Dakota on Sunday after what his office said was a negative reaction to medication.
"Tim is in good hands and in good spirits. We want to thank everyone for their prayers and support," Johnson's wife, Barb Johnson, said.
Johnson was first elected to the Senate in 1996 and easily won re-election to a third term in 2008.
–CNN Senior Political Editor Mark Preston contributed to this report