Merck & Co has been subpoenaed by the US Department of Justice as part of a criminal investigation into marketing practices for three prescription medicines.

The products in question are Temodar (temozolomide) for brain cancer and hepatitis C and cancer drugs PegIntron (pegylated interferon alfa-2b) and Intron A (interferon alfa-2b), according to Merck's just-published quarterly report. All three of the drugs were acquired when Merck bought Schering-Plough in 2009.

"The DoJ has issued a subpoena requesting information related to the company's marketing and selling activities with respect to Temodar, PegIntron and Intron A from January 1, 2004 to the present," said Merck, adding it is cooperating with the investigation.

Merck is also under investigation for marketing of now-defunct arthritis drug Vioxx (rofecoxib), and last year set aside a $950 million reserve fund to cover future liabilities in the case.

The firm is also being probed by the DoJ and Securities & Exchange Commission about activities in a number of countries under the terms of the USA's Foreign Corrupt Practices Act, but says it believes this inquiry is part of a "broader review of pharmaceutical industry practices in foreign countries."

Last year, Schering-Plough was accused of paying kickbacks to doctors in Vietnam in return for prescribing PegIntron.

J&J reaches tentative settlement

Meanwhile, another company caught up in mismarketing probes - Johnson & Johnson - has reached an agreement in principal to settle a misdemeanour criminal charge brought by the DoJ related to its antipsychotic drug Risperdal (risperidone), according to an SEC filing.

J&J had been charged with promoting Risperdal for unapproved uses and downplaying risks associated with its use such as weight gain and diabetes.

Other criminal and civil suits are still active, says the firm, which has been under investigation for Risperdal marketing practices since 2004. The company's follow-up antipsychotic drug, Invega (paliperidone), is also under scrutiny.