European regulators raided some of the world’s biggest pharmaceutical companies on Wednesday in an inquiry into whether they conspired to keep up the price of drugs after patents expired.

Pfizer, GlaxoSmithKline, AstraZeneca and Sanofi-Aventis were among those that confirmed they had been visited as part of a European Commission-led probe into delays in the launch of low-cost generic drugs. Teva, the world’s biggest generics company, was also targeted.