Pershing Square, the investment firm run by activist investor Bill Ackman, said Friday it settled a lawsuit with Allergan, the maker of Botox, related to Allergan’s poison pill plan and Pershing’s $53 billion offer for the company.

Pershing Square sued to make sure that its call for a special meeting of shareholders wouldn’t trigger a defensive “poison pill” plan designed to make a hostile takeover prohibitively expensive. Pershing owns almost 10 percent of Allergan Inc.

Pershing and Valeant Pharmaceuticals International Inc. went public with their takeover attempt in April and have increased their offer several times. The current offer is $72 per share. Allergan has repeatedly rejected those offers as underpriced and risky, prompting Pershing and Valeant to go straight to the company’s shareholders.

Pershing said the settlement of the lawsuit paves the way for it to call a special shareholder meeting to ask Allergan shareholders to back its offer, without fear of triggering the poison pill.

Allergan shares rose $2.01 to $172.56 in afternoon trading.