He had been designated for assignment to Triple-A Oklahoma last Friday and was released after clearing waivers.
"When we signed him, we hoped he could give us enough innings or regain his form," said Manager Bob Melvin. "Pedro pitched some good games for us, but not at the level that he needs to pitch."
The Rangers had 10 days to release Astacio outright or trade him. The Dallas Morning News reported the team has decided to eat the remainder of his approximately $950,000 in salary and bonuses.
The 14-year veteran is 120-117 with a 4.66 ERA in 363 games while pitching for the Rockies, Astros, Mets and Red Sox.
Astacio had struggled this season, going just 2-8 in 12 starts with a 6.04 ERA and had lost seven of his last eight decisions.