Following a three-week run-in period (Period I) during which participants received placebo, participants entered into a 12-week double-blind treatment period (Period II) during which they received daily doses of either one of three doses of MK-0873 or placebo. Period I and Period II made up the Base Study. Following the 12-week treatment period in the Base Study, participants were invited to continue in an optional 12-week double-blind extension study (Period III, EXT1). Participants who received any dose of MK-0873 in the Base Study continued on MK-0873 2.5 mg daily in Period III while participants in the placebo arm of the Base Study continued on placebo daily. Following EXT1, participants were invited to continue in an optional open-label second extension study (EXT2) which was to last 80 weeks (Period IV: 28 weeks, Period V: 52 weeks). In EXT2, participants who had been taking MK-0873 2.5 mg in the Base Study were allocated to MK-0873 2.5 mg plus usual care, while participants who had been taking the other two doses of MK-0873 or placebo in the Base Study were allocated to either MK-0873 2.5 mg plus usual care or to usual care alone.