Pfizer's failed $160bn bid for Allergan is the largest withdrawn deal on record

Caitlin Morrison
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If it had completed, it would have been the biggest M&A deal on record (Source: Getty)

The giant pharma deal thwarted by new US tax inversion rules is the biggest transaction that has ever been withdrawn, according to financial software firm Dealogic.

Viagra-maker Pfizer's $160bn (£113bn) takeover of Botox manufacturer Allergan was called off yesterday, following the introduction of new rules by the US Treasury.

It was thought that US firm Pfizer was aiming to move its headquarters to Ireland, where Allergan is registered, through the deal. Ireland's corporation tax rate is one of the lowest in the world.

However, on Monday the US government said it would be imposing stricter rules aimed at prohibiting such transactions, known as inversion deals.

According to Dealogic, if the Pfizer/Allergan tie-up had completed, it would have been the second largest M&A deal on record, after Vodafone Airtouch's $172bn acquisition of Mannesmann in 2000.

Dealogic also noted that there have been 23 completed tax inversion deals since 2011, with a total value of $243bn.