(Adds details on Allergan's debt, dividend)
Sept 25 (Reuters) - U.S. drugmaker Allergan Plc on Monday authorized a $2 billion buyback of its common stock, sending its shares up after a week of grim news on its drug development pipeline.
Allergan shares have fallen by around a fifth in value since late July but were up 1.4 percent in premarket trading after the announcement, in which it also said its Chief Financial Officer Tessa Hilado would retire.
The planned stock buyback follows its completion of a separate $15 billion repurchase, and also after it reported mixed trial data for its experimental treatment of NASH liver fibrosis.
The company said it had begun the search for a new finance chief but gave no initial response to Reuters requests for more details on Hilado's departure.
Allergan, which said it was committed to boosting its dividend payout annually, also backed its 2017 financial guidance and its commitment to pay down $3.75 billion of debt in 2018.
Hilado, 53, joined the company in 2014 and will continue in her current role until a successor is named.
The company last week also got a "refusal to file" letter from the U.S. Food and Drug Administration for an expanded approval for its Vraylar for treatment of negative symptoms associated with schizophrenia in adult patients.
Allergan had $30.24 billion in current and long-term debt and capital leases as of June 30. (Reporting by Manas Mishra in Bengaluru; Editing by Sai Sachin Ravikumar)