New US tax evasion rules scupper Pfizer-Allergan deal

US drug maker Pfizer has agreed to terminate its $US160 billion ($A212.30 billion) agreement to acquire Botox maker Allergan, in a major victory to US President Barack Obama's drive to stop tax-dodging corporate mergers.

The decision to end the biggest tax "inversion" ever attempted, which would have seen Pfizer slash its tax bill by redomiciling to Ireland where Allergan is registered, came a day after the US Treasury unveiled new rules to curb inversions.

While these new rules did