Human Genome Sciences, also known as HGS, wanted the companies to use a "strategic alternatives review process" before any possible deal, it said. Instead, GlaxoSmithKline today opted to offer HGS shareholders an 81 percent premium on their stock value with a per-share purchase price of $13. GlaxoSmithKline first announced its bid to buy HGS in April.

HGS developed technologies for two drugs GlaxoSmithKline is working on, including one entering clinical trials to treat heart disease and stroke, and another to control blood sugar levels and appetite.

HGS trades its shares on the Nasdaq under the ticker symbol HGSI.

GlaxoSmithKline, which has its vaccine filling and packaging plant in East Donegal Township, trades its shares on the New York Stock Exchange under the symbol GSK.