FDA places Arrowhead Hep B drug on partial hold, shares plunge

(Adds details, background, updates share movement)

Jan 12 (Reuters) - Drug developer Arrowhead Research Corp (NasdaqGS: ARWR - news) said the U.S. Food and Drug Administration placed the company's experimental hepatitis B treatment on partial clinical hold, seeking additional data from the drug's mid-stage study.

The company's shares plunged 22 pct premarket on Monday after the FDA also asked the company to reduce the dosage of the drug, ARC-520.

The FDA requested Arrowhead to begin the multiple-dose trial for the drug at 1mg/kg - much lower than the company's proposed 2 mg/kg and 4 mg/kg.

The regulator also requested additional information on patients who received 1-4 mg/kg of the drug in the ongoing single-dose mid-stage trial and report from the ongoing multiple-dose non-clinical study.

Arrowhead said its ongoing mid-stage trial would continue as planned and that it expected to file with Asian and European agencies to begin additional mid-stage studies in coming weeks.

Arrowhead's shares jumped 66 percent in the 30 days through Friday's closing, in part due to speculation that the company could be a takeover target for larger drugmakers.

Shares (Dusseldorf: DI6.DU - news) of the Pasadena, California based company closed at $9.06 on Nasdaq on Friday. (Reporting by Anjali Rao Koppala in Bangalore; Editing by Saumyadeb Chakrabarty)