LONDON — The British drug maker GlaxoSmithKline changed the terms of its $2.59 billion proposed takeover of Human Genome Sciences on Wednesday in response to the biotechnology company’s shareholder rights plan, or poison pill.

Last week, Human Genome Sciences had adopted the poison pill, which activates when a third party acquires 15 percent of the company’s stock, as a defensive strategy to ward off Glaxo’s takeover approach.

In response, Glaxo said it had added a condition to its bid, requiring Human Genome Sciences to either redeem the poison pill or ensure that the strategy did not block Glaxo’s approach for the company.

Glaxo has given shareholders in Human Genome Sciences until June 7 to agree to its $13-a-share offer.

The Human Genome Sciences board has already rejected the offer, saying it undervalues the company. While shares in the company are currently trading around $14, the stock has fallen approximately 50 percent in the last 12 months.

Despite rejecting Glaxo’s bid, Human Genome Sciences has said it is looking at its strategic options, which might lead to the company sell itself.

The company, which had asked Glaxo to participate in the discussions, said it was in talks with a number of pharmaceutical and biotechnology companies about a potential sale, though no decision had been made.

Lazard and Morgan Stanley are advising Glaxo on the deal, while Credit Suisse and Goldman Sachs are advising Human Genome Sciences.

Article source: http://dealbook.nytimes.com/2012/05/23/glaxo-amends-2-59-billion-takeover-offer-for-human-genome-sciences/?partner=rss&emc=rss