Four pharmaceutical companies have been accused by the Competition and Markets Authority (CMA) of breaking competition law.

The CMA accused Auden Mckenzie and King Pharmaceuticals of sharing between them the supply of the anti-depressant drug nortriptyline to what it described as “a large pharmaceutical wholesaler.”

It was alleged that in 2014, the two companies agreed Auden Mckenzie would supply only 10mg nortriptyline tablets and King Pharmaceuticals would supply only 25mg nortriptyline tablets. The companies were accused of agreeing to fix the quantities and prices of supply.

The CMA also accused King Pharmaceuticals, Alissa and Lexon of “exchanging commercially sensitive information, including information about prices, volumes and entry plans, to try to keep Nortriptyline prices high.”

The CMA said NHS spending on nortriptyline peaked at £38 million in 2015. It has given the four companies the opportunity to respond to the allegations which, if proven, could result in a fine of up to 10% of a business’s annual global turnover.

It is the second time in less than a month that Lexon has been accused of breaking competition law by the CMA.

On May 23, the CMA alleged Lexon, Alliance Pharmaceuticals, Medreich and Focus colluded to increase the price of an anti-nausea drug to the NHS by 700%.

Earlier this month Nitin Sodha, who is a director of Lexon, stepped aside as chairman of the National Pharmacy Association while the CMA investigated the allegations.

“The CMA has provisionally found that King and Auden Mckenzie’s conduct, and the subsequent conduct of King, Alissa and Lexon, broke competition law,” the CMA said.

Geoff Steadman, director of antitrust at the CMA, said: “If pharmaceutical companies get together to restrict competition for the supply of a drug, this can lead to the NHS, and ultimately the UK taxpayer, paying over the odds for what are often essential medical treatments.

“We expect drug suppliers to abide by competition law so that the NHS is not denied the opportunity of benefitting from lower prices for medicines.”