(Adds GSK statement)

April 13 (Reuters) - Drug company Innoviva Inc said on Thursday it would undertake a review of its costs, including executive compensation following pressure from activist investor Sarissa Capital Management LP.

The news comes two weeks after hedge fund Sarissa Capital called for a sharp cut in the compensation of Innoviva's chief executive and the board.

The review will be conducted by a special committee of the company's independent directors and is expected to be out by third quarter of this year, Innoviva said.

GlaxoSmithKline Plc, which has a 29.3 percent stake in Innoviva and is its biggest shareholder, said it supports the company's efforts to deliver significant shareholder value.

Innoviva has a partnership with Britain's GSK, and the companies submitted an application in November to market their new three-in-one inhaled lung drug for U.S. approval.

GSK also said it intends to vote for Innoviva's board nominees at the annual shareholder meeting scheduled for April 20. (http://bit.ly/2ocTHJJ)

Sarissa, run by billionaire investor Carl Icahn's former healthcare lieutenant Alex Denner, has lately criticized the drug company's cost structure as the two sides square off in a proxy contest.

The hedge fund, which owns 2.72 percent of Innoviva, according to Thomson Reuters data, in March nominated three directors to Innoviva's board.

Innoviva shares were marginally down after the bell. (Reporting by Divya Grover in Bengaluru; Editing by Shounak Dasgupta)