To make room for Ramirez, right-handed pitcher Tim Melville was designated for assignment.
"When we signed him, we looked really hard at why he wasn't having the success in the big leagues you would think he would have with his type of stuff," manager Bryan Price said of Ramirez. "A lot of it was how he used his pitches, what sides of the plate he used and where he got in trouble. We identified that, and that was really the challenge we gave to him when he was sent to Louisville: 'Go out there and make the changes.'
"He doesn't have to change his delivery or change the way he grips his pitches, but he did have to be aware that another good season in Triple-A and coming up and struggling in the big leagues would be repeating the past several years. We want to do something about that."
Ramirez, 27, logged six scoreless innings over five games with Louisville. He allowed four hits, issued three walks and struck out 10 batters. At Spring Training, he was cut the day before the Reds broke camp.
"It's just throwing strikes and getting ahead," Ramirez said. "They told me in Spring Training when they sent me down that I have to use more sliders in any count. That's pretty much what I was doing over there, throwing my slider in any count and any situation that I could. I think I showed those guys that I could do that, and maybe that's why I'm here right now."
Ramirez has a 6.42 ERA over 38 career Major League games with the Phillies, D-backs and Mariners. He pitched last season for Arizona and Seattle, posting a 5.32 ERA with 11 walks and 16 strikeouts in 23 2/3 innings over 20 relief appearances. As Cincinnati reworked its bullpen in the offseason, Ramirez saw opportunity.
"I saw what was going on with the team, and I knew it was the right situation for me," Ramirez said. "I know myself. I know what kind of pitcher I am. I'm trying to get to the big leagues and stay here for a long time.
The 26-year-old Melville pitched in his first three Major League games this season, two of which were starts. He surrendered 11 earned runs in nine innings. Four runs and five hits came during a two-inning relief appearance during Thursday's 16-0 loss to the Cubs.
• Starter Alfredo Simon (right biceps tendinitis) had a smooth bullpen session on Friday. Simon, who was skipped from his last start, is still slated to start against the Cubs on Sunday.
• Right-hander Keyvius Sampson cleared waivers and was sent outright to Louisville.
Mark Sheldon has covered the Reds for MLB.com since 2006, and previously covered the Twins from 2001-05. Read his blog, Mark My Word, follow him on Twitter @m_sheldon and Facebook and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.