The Chinese patent office has rejected a patent application for the blockbuster hepatitis C treatment sofosbuvir, increasing the possibility of a generic version of the drug to become available in China.

The decision comes after a challenge by the Initiative for Medicines, Access and Knowledge (I-MAK), a US based group that campaigns for better access to affordable drugs. The group claimed that Gilead Sciences, the US biotechnology company that makes sofosbuvir, which recorded sales of more than $10bn in 2014, was seeking “illegitimate patents” for sofosbuvir and "blocking millions".