The San Diego Padres activated pitcher Sean O'Sullivan from the paternity list on Thursday.

The right-hander has a record of 0-2 with an ERA of 3.72 in four appearances -- three starts -- with the Padres this season since being called up from Tucson, their Triple-A affiliate. The 25-year-old went 7-4 with an ERA of 3.88 with Tucson.

The Padres also optioned pitcher Miles Mikolas to Tucson. The right-hander appeared in two games of relief for the Padres.