Merck & Co. Inc. today said its HIV medication Isentress was granted a license for distribution in the 27 European Union member countries, plus Iceland and Norway.

The drug - a new therapy for AIDS patients resistant to existing treatments - is taken twice daily as a single pill.

Merck, of Whitehouse Station, N.J., said the licensing, following a positive opinion from the European Medicines Agency, was based on efficacy and safety data from two double-blind, 24-week clinical trials in adults.

The medication, also called raltegravir, was approved for use along with other AIDS medications. It was cleared for use in the U.S. in October. Analysts said the medication, Merck's first HIV therapy since 1999, may generate as much as $1 billion in annual sales worldwide.

Studies for use of Isentress for pediatric patients are underway, Merck said. The company has major operations in the Philadelphia area.

Shares were up 13 cents, to $58.67 in midday trading on the New York Stock Exchange.