Par Pharmaceuticals has reported a first quarter loss in the wake of falling drug sales and a large legal charge.

The US-based pharmaceutical firm faced a $196m legal settlement relating to claims that the company inflated wholesale drug charges improperly.

The company posted a lost of approximately $109m, compared to a profit of $26.3m during the corresponding year ago period, while revenue fell 20% from $291.9m to $233m.

The loss of revenue is largely attributable to disappointing sales of metoprolol, the generic version of heart drug Toprol XL, which fell 13% to $63.4m amid increasing competition from other generics.