The Pirates optioned Eisert to Triple-A Indianapolis on Wednesday, Jason Mackey of MLB.com reports.
Eisert was needed for 2.1 innings and 41 pitches in Tuesday's extra-innings loss to the Diamondbacks, so he's being replaced by a fresh arm. The lefty holds a 6.29 ERA and 40:12 K:BB over 34.1 innings between the White Sox and Pirates this season.