The National Health Service is suing seven pharmaceutical companies for £30m over allegations they fixed the price of common antibiotics.
Documents lodged with the High Court claim the firms agreed to artificially raise the price of a range of penicillin-based drugs.
The case is part of a massive investigation into alleged drug frauds worth a total of up to £200m which may lead to further court action.
The Serious Fraud Office is also looking into allegations of drug pricing fraud.
The antibiotics case follows a £28m action brought against six companies last year.
It was alleged they conspired to restrict the supply of the blood-thinning agent warfarin to increase its price.
All those being sued are involved in the production of generic "copycat" versions of drugs on which the original patents have run out.
It is alleged that they agreed to artificially inflate the price of particular antibiotics known as cillins in 1997 and 1998 by reducing supply and refusing to sell below an agreed price.