The UK’s Competition and Markets Authority (CMA) has provisionally ruled that a discount scheme operated by US drugmaker Merck for Remicade may have broken competition rules by restricting competition from cheaper biosimilar versions.

Following an investigation that started in December 2015, the watchdog said it believes the company abused its dominant position, although stressed that findings are provisional and it will carefully consider any representations by the company.

Remicade (infliximab) is a top seller for Merck, generating annual revenues of more than $10 billion. The drug is used mainly to treat patients with gastroenterology and rheumatology conditions such as Crohn’s disease, ulcerative colitis and rheumatoid arthritis. Cheaper versions of the drug entered the European market in February 2015 when the patent expired.

Merck Sharp & Dohme (MSD), the international arm of US Merck, said it is confident proceedings will show it has complied with competition law at all times. “The discounts in question meant that infliximab was competitively priced and offered savings to the UK National Health Service, without hindering competition,” the company stated. CMA said it proposed to find MSD and parent Merck “jointly and severally liable” for the alleged infringement.

According to media reports, MSD announced in October 2015 that it would offer the NHS discounts amounting to £48 million on sales of £191 million after the National Institute for Health and Clinical Excellence (NICE) approved both Remicade and biosimilar versions.