Caremark ( CMX) boosted its stock-buyback plan to $750 million and reaffirmed second-quarter guidance early Tuesday. The Nashville, Tenn., pharmacy benefit manager said it expected to post earnings next week of around 30 cents a share. That's up from 26 cents a year earlier and in line with the Thomson First Call analyst consensus estimate. Caremark said it expanded its stock-repurchase authority from the previous $150 million. The company said it had bought back $133 million worth of stock under that plan. The news comes as Caremark confronts rising legal concerns about its business practices stemming from a whistleblower suit. Attorneys general from 19 states have already said they'd look into Caremark's business. On Monday, TheStreet.com reported that a lawyer connected with the case said he'd received a federal subpoena. Caremark, which has previously defended its practices, said it hasn't gotten a subpoena and doesn't expect to. On Monday, Caremark closed at $31.34.