Novartis has added to its clinical pipeline once again by exercising an option to license a hepatitis C drug developed by Idenix Pharmaceuticals and acquiring an antidepressant from Servier.

The Swiss drugmaker is paying up to $525 million to Idenix to secure rights to valopicitabine, pledging its support to the project just days after the latter company said it would delay Phase III trials of the compound after seeing gastrointestinal side effects with the drug. Idenix now plans to test it at lower doses.

Financial terms of the agreement with Servier have not been disclosed, but the deal gives it rights to agomelatine, currently in Phase III trials for major depressive disorder. This novel antidepressant acts as a melatonin receptor agonist/serotonin 5-HTc antagonist, and has shown good efficacy, including in severe depression, and a more favourable side effect profile than currently-available antidepressants.

The two latest deals follow hard on the heels of Novartis’ just-announced $515 million deal with SGX Pharmaceuticals for leukaemia drugs, and a $400 million deal earlier this month with Infinity Pharmaceuticals for cancer drugs targetting Bcl-2.

Under the terms of the Idenix deal, Novartis will pay $25 million on taking up the option, with an additional $45 million due when valopicitabine advances into Phase III testing for hepatitis C. The balance of the deal – some $455 million – will be payable on regulatory filings and approvals in the USA, Europe and Japan.

Novartis owns 56% of Idenic and is also working with the firm on two drugs for hepatitis B, including telbivudine which has been filed for approval in Europe and the USA and valtorcitabine in Phase IIb. Last year it signed a $570 million deal with Anadys Pharmaceuticals for ANA975, another hep C candidate.