NEW YORK (TheStreet) -- Shares of Arrowhead Research  (ARWR - Get Report) plummeted 26.38% to $6.67 in morning trading Monday after the FDA instituted a partial clinical hold on the drug developer's potential hepatitis B treatment.

The FDA asked the company to reduce the dosage of its experimental hepatitis B treatment in a mid-stage trial and also requested additional trial data from Arrowhead. The FDA requested that the company start the multiple-dose study at one milligram of the experimental drug per kilogram, rather than Arrowhead's proposed parallel study design of two and four milligrams per kilogram.

Arrowhead said the ongoing mid-stage trial would continue as planned. The company still expects to file with Asian and European agencies to start additional mid-stage trials in the next few weeks.

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ARWR Chart ARWR data by YCharts

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