Pfizer has extended its deadline to gain complete control of pain therapy specialist Icagen amid continuing difficulties in persuading shareholders to part with their stakes in the company.

Pfizer owned around 11% of Icagen when the $6-per-share offer was first announced in July, and had set an initial deadline of August 31 to garner enough of a stake to allow the takeover to proceed. That was extended to September 1 and then September 2 after Pfizer failed to meet that target.

No announcements have been made since the last deadline passed. By the end of August 31 Pfizer owned around 49% of Icagen, and was just 40,000 shares short of gaining control.

The pharma multinational has been trying to buy around 8.3 million outstanding shares in Icagen, valuing the transaction at $56 million, but is facing resistance from some shareholders who believe the offer is too low. Prior estimates had valued the firm at around $8 per share, and there have been allegations of conflicts of interest among some members of Icagen's board of directors.

Icagen and Pfizer have been working together since 2007, collaborating on a project to develop compounds that modify sodium ion channels and could represent a new class of therapies for pain and related disorders.

In addition to the pain programme, Icagen is developing a novel opener of the KCNQ potassium ion channel with potential in the treatment of both pain and epilepsy. The compound, called ICA-105665, has completed Phase I testing.