GlaxoSmithKline said Wednesday that first-quarter, after-tax profit dropped about 13 percent compared to the first quarter of 2011.

The global pharmaceutical manufacturer is based in London, but has operations in Center City and in Philadelphia suburbs.

The decline can be attributed at least partially to the absence of the one-time payment in 2011 for GSK's interest in Quest, the U.S. laboratory diagnostic company.

GSK had after-tax profit of $2.55 billion in the first quarter in 2011, but that figure dropped to $2.24 billion in 2012.

Sales in the United States grew nine percent for GSK products, while Europe had a six percent decline.

"We remain mindful of the challenges we face given the current global political and economic environment, particularly in relation to pricing on our more established products," chief executive officer Sir Andrew Witty said in a statement.

"However, we also continue to see attractive growth opportunities across our businesses and we intend to continue to invest behind them to strengthen the breadth and mix of the Group and its future growth prospects. 2012 is a very important year for pipeline delivery and so far the performance has been encouraging. This year we have received a significant amount of positive data for five Phase III assets for the treatment of HIV, cancer, diabetes and asthma."