GlaxoSmithKline and Novartis said on Monday they had completed a series of asset swaps worth more than $20 billion that will reshape both drugmakers.

GSK is forming a consumer health joint venture with Novartis, while at the same time buying the Swiss company's vaccines business and divesting its cancer drugs portfolio to Novartis.

The two companies originally announced the transactions in April 2014 to bolster their best businesses and exit weaker ones as the drugs industry contends with healthcare spending cuts and increased generic competition.

GSK, which now plans to return GBP4 billion ($6.2 billion) to shareholders, said it would provide an in-depth view of its prospects at an investor meeting to be held when it reports first-quarter results on May 6.

The complex deals are more significant for GSK than for Novartis, reflecting the fact that the British group's market value is less than half that of its Swiss rival.

After holding off from providing financial guidance for this year when it reported annual results last month, GSK said it would provide 2015 earnings guidance and "profile the medium and long-term shape and opportunities" of the group on May 6.

The transactions come at a critical time for the British drugmaker, which will see new chairman Philip Hampton take over on May 7.

Hampton, who chairs Royal Bank of Scotland, takes the reins following a tough year at GSK, which was hit by a record fine of nearly $500 million in China for bribing doctors and has disappointed investors with weak lung drug sales.

The poor performance resulted in the bonus paid to Chief Executive Andrew Witty for 2014 being cut by 51 per cent.

GSK is receiving net after tax proceeds from the Novartis transactions of $7.8 billion, the majority of which will be distributed to shareholders through a so-called B share scheme.

For Novartis, the asset swaps will boost the company's already substantial presence in oncology and are expected to lift core margins immediately.

The Swiss drugmaker now has a portfolio of 22 oncology and haematology medicines, with the GSK deal providing new therapies in melanoma, kidney and blood cancers.

Novartis is paying $16 billion for GSK's cancer drugs, although up to $1.5 billion of this may have to be returned to Novartis if GSK's melanoma drugs fail to meet expectations. GSK believes the necessary conditions will be satisfied, after recent positive clinical trial results.

On top of the transactions with GSK, Novartis also sold its animal health business to Eli Lilly. – Reuters