Paronto and Sadler have the right to refuse the outright assignment and become free agents, while Duran will be placed on the roster at Triple-A Round Rock.
Duran, 25, was claimed off waivers by the Astros from the Rangers on July 1 and never appeared in a Major League game for them this year. He started his stint with the organization on the disabled list while recovering from an appendectomy and hit .167 with one home run and 10 RBIs in 43 games between Triple-A Oklahoma, Double-A Corpus Christi and the Astros' Gulf Coast League affiliate.
Paronto, 34, finished the season with no decisions and a 12.15 ERA in six appearances over two stints for the Astros in 2009. He spent the majority of the season at Round Rock, posting a 1.39 ERA and 24 saves for the Express.
Sadler, 28, made one relief appearance for Houston this season before being placed on the 60-day DL with right shoulder dyskinesis on Sept. 10. Signed to a Minor League contract by the Astros on Aug. 6, Sadler spent most of this season in the Astros' and Giants' Minor League systems, compiling a 5-3 record and a 4.98.
The Astros 40-man roster now stands at 38.
Brian McTaggart is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.