Drugmakers Pfizer Inc and Flynn broke competition law by charging Britain's National Health Service (NHS) "unfairly high" prices for an epilepsy medicine, a regulator said on Thursday after reassessing a fine imposed in 2016.

The companies made use of a regulatory loophole so that the capsules, branded Epanutin prior to September 2012, was not subject to price regulation for branded drugs, the UK's Competition and Markets Authority (CMA) found in its provisional review.

In 2016, Britain fined Pfizer and Flynn a record 90 million pounds ($124.92 million) for the price hike. However, the companies in 2018 won an appeal against the fines.

A 100mg pack cost 67.50 pounds, a 2,600% jump from earlier prices, before it was reduced slightly to 54 pounds apiece from May 2014, the CMA said in its 2016 order.

The CMA said on Thursday that spending by the NHS on the capsules, containing phenytoin sodium, jumped to roughly 50 million pounds ($69 million) in 2013 from about 2 million pounds a year just a year earlier.

"As Pfizer and Flynn were the dominant suppliers of the drug in the UK, the NHS had no choice but to pay unfairly high prices for this vital medicine," the watchdog said.

Both Pfizer and Flynn did not immediately respond to a request for comment.

($1 = 0.7205 pounds)

(Reporting by Pushkala Aripaka in Bengaluru; editing by Uttaresh.V and Rashmi Aich) ((Pushkala.A@thomsonreuters.com; Twitter: @pullthekart; Mobile: +91 852 751 3793 ;))