PITTSBURGH — Mayor Bob O'Connor's brain tumors seem to be responding to his first dose of chemotherapy, but he likely won't return to his office for several weeks, doctors said Wednesday.

O'Connor, 61, who had been expected to be released from University of Pittsburgh Medical Center several days ago, was fatigued and probably will remain in the hospital a few more days because of some of the side effects of the treatment, doctors said.

"It's been a tough week for him," said Dr. Frank Lieberman, a neuro-oncologist.

When O'Connor is released, he will work from home. Doctors said he likely won't return to his office until late August or early September.

O'Connor was given a high dose of steroids to relieve swelling near the tumors. The steroids caused severe hiccups, which prevented the mayor from sleeping and caused significant pain. Doctors struggled to keep the hiccups under control, at one point trying lemon wedges soaked in bitters to alleviate them, they said.

The steroids also caused the mayor to retain fluids and prevented his body from clearing the chemotherapy drug methotrexate, which can cause liver damage, doctors said.

Doctors had planned this week to give the mayor Temodar, a second cancer-fighting drug. They decided to delay that treatment until his liver profile, which had been abnormal, returned to normal.

The mayor was taking low doses of morphine to alleviate pain as well as a muscle relaxant to help control the hiccups. The drugs caused him considerable fatigue, doctors said.

O'Connor's physicians initially had said the mayor might be able to return to work as soon as two weeks after his initial chemotherapy treatments.

"Frankly, he needs time to recover," said Dr. Stanley Marks, one of O'Connor's oncologists. "Perhaps we were a little over-optimistic last week."

Although the mayor's treatment caused painful and persistent side effects, a CT scan on Sunday indicated that the high-dose methotrexate is killing the cancer cells in his tumors, doctors said.

The mayor is working from the hospital, and a spokesman said no deputy mayor has been named to replace O'Connor.

"The mayor is in charge of the city," spokesman Dick Skrinjar said. "His doctors say he is not disabled. ... The business of government continues."

Skrinjar compared O'Connor to an architect who designs a building plan while others carry out its construction.

A Democrat who took office in January, O'Connor was diagnosed with a rare form of primary central nervous system lymphoma. He has small tumors on his brain, but doctors have said his neurological profile is normal and that he should eventually be able to resume his official duties.

O'Connor was admitted to the hospital almost two weeks ago after complaining of flulike symptoms.