DUBLIN, Nov 4 (Reuters) - Ireland's High Court on Wednesday refused to quash a 1.64 billion euro ($1.91 billion) back tax demand against Perrigo relating to the drugmaker's acquisition of Ireland's Elan Pharma in 2013.

Perrigo said in a statement that no payment was required as a result of the High Court ruling, which it said it would consider appealing. If the High Court ruling is not appealed, the matter is due to go before Ireland's Tax Appeals Commission.

The back-tax demand, issued in 2018, was one of the biggest ever made in Ireland.

The tax authority in 2018 found that intellectual property (IP) sales by Elan Pharma, including multiple sclerosis drug Tysabri, were taxed as trading income at 12.5%, when they should have been treated as a chargeable gain at a rate of 33%.

Perrigo challenged the ruling in the High Court, contending the Irish tax authority was incorrect in characterising the sale of the IP as a capital transaction.

"Perrigo has failed to establish any basis to interfere with the assessment issued in respect of the disposal of the Tysabri IP and, accordingly, its claim must be dismissed," Wednesday's High Court ruling said.

($1 = 0.8570 euros) (Reporting by Conor Humphries; Editing by Edmund Blair and Mark Potter)