Pharma stocks, especially those which have large exposure to United States, saw knee-jerk reaction on Friday after a media report indicated that US prosecutors are undertaking an investigation into suspected price collusion.

Shares of Sun Pharma , Dr Reddys Labs , Aurobindo Pharma , Cadila Healthcare , Lupin and Glenmark Pharma , which get around 30-50 percent revenue from worlds largest drug market, crashed 5-8 percent intraday Friday. Sun Pharma touched 52-week low of Rs 654.70 per share.

The antitrust investigation by the US Justice Department, begun about two years ago, now spans more than a dozen companies and about two dozen drugs, a media report said quoting people familiar with the matter.

The report further said a grand jury probe is examining whether some executives agreed with one another to raise prices, and the first charges could emerge by the end of the year.

According to the report, companies that are believed to have received subpoenas are Mylan NV, Teva Pharmaceutical Industries, Actavis, Lannett, Impax Laboratories Inc, Covis Pharma Holdings, Sun Pharmaceutical Industries, Mayne Pharma, Endo Internationals subsidiary Par Pharmaceutical Holdings and Taro Pharmaceutical. Post the report, share prices of pharma companies that are listed on Nasdaq tanked between 7-27 percent yesterday.

Sources from Dr Reddys Laboratories told CNBC-TV18 that the company had received subpoenas around 1-1.5 years ago from US regulators and had responded with adequate information on the same. Subpoena was related to price increases in the US market.