ROME (Reuters) - Prosecutors in Rome have opened an investigation into four executives at Swiss drugmakers Roche (>> Roche Holding Ltd.) and Novartis (>> Novartis AG) on suspicion of fraud and manipulation of the pharmaceutical market, judicial sources said on Friday.

Earlier this month, Italy's antitrust authorities said Roche and Novartis colluded to try to stop cancer drug Avastin from being used to treat a serious eye disease and fined the companies 182.5 million euros ($251 million).

A Novartis spokesman had no immediate comment, while a Roche spokesman referred to the company statement issued after the antitrust ruling that called the charges "unfounded" and said it would appeal.

(Reporting by Mario Sarzanini in Rome and Caroline Copely in Zurich; writing by Steve Scherer)

Stocks treated in this article : Roche Holding Ltd., Novartis AG