Shire has extended its tender offer to buy ViroPharma for a second time, now expiring on midnight January 23.

The tender offer was originally scheduled to expire at midnight New York City yesterday (January 9) and has now been extended to January 23. It already been extended before, from December 26, and Shire notes that it has received valid acceptances representing 78% of ViroPharma's stock.

Shire agreed to buy ViroPharma for around $4.2 billion in cash in November, giving it access to the hereditary angioedema drug Cinryze (C1 inhibitor [human]), which complements its own HAE drug Firazyr (icatibant). The purchase is expected to help the firm's rare diseases business revenues pass $2 billion this year  and Shire is looking at $150 million of annual cost synergies across the group by 2015.