After a 40%-plus decline in its stock price, growing unease in its executive corps and ample speculation about the company's future following its damaging recall of Vioxx, beleaguered drugmaker

Merck

(MRK) - Get Report

is getting defensive by adopting a severance plan for some two-dozen top managers.

In a

Securities and Exchange Commission

filing, Merck said the plan is "part of its ongoing, periodic review of its compensation and benefits programs," adding it is also intended to avoid "the distraction and loss of key management personnel that may occur in connection with rumored or actual fundamental corporate changes."

The severance plan would become operative under a "change of control" at the company, based on various circumstances, which include a merger or acquisition.

The plan provides severance benefits "upon qualifying terminations of employment in connection with or within two years following a change in control of the company." The plan covers 230 employees, including members of the company's management committee and other vice president-level managers.

Under the plan, employees would receive salary and bonus payouts, as well as continued benefits and other financial and service perks.

The plan makes Merck a less attractive and more expensive takeover target, but also makes it more costly if and when competitors poach its employees.

Shares rose 23 cents, or 0.8%, to $27.93 in premarket trading Monday.