The company's stock sank $1.86, or nearly 6%, to $30.34 in late morning trading on the New York Stock Exchange.

Nashville-based Caremark said it received an information request, known as a civil investigative demand, on Thursday from Washington state's attorney general. The administrative subpoena concerns consumer protection statutes and business practices of Caremark and its recently acquired AdvancePCS unit, the company said.

State officials in Washington told Caremark that 18 other states would follow with their own investigative demands, the company said.

The probe follows federal and state inquiries into pharmacy benefit managers like rival Medco Health Solutions. The companies, which act as brokers between employers and drug makers, are accused of steering doctors to pricier drugs to boost profits, among other charges.

The demands "appear to request information from us relating to issues that are similar to those addressed in other recent industry settlements," Caremark spokesman Gerard Carney said.

Caremark believes its business practices "comply in all material respects with applicable laws and regulations. The company intends to fully cooperate with the requests for information," it said in a statement.

A call to Caremark seeking additional information was not immediately returned.

The investigation comes as Caremark continues to deal with a separate controversy involving two Florida pharmacists who worked in the company's mail-order unit.

Michael and Peppi Fowler filed a lawsuit in 2003 alleging that the company routinely resold drugs that other patients returned without testing the medication to see if they had been tampered with.

Last month, Caremark, in an unusual twist, said it backed a motion filed by the Florida attorney general to intervene in the case.