TOKYO, Dec 22 (Reuters) - Japan's Nikkei share average was flat on Friday morning as gains in commodities trading houses offset weakness in drugmakers, while Kobe Steel stumbled after it said senior executives were aware of data tampering.
The Nikkei was flat at 22,869.58 in midmorning trade. For the week, it has gained 1.4 percent so far, the biggest weekly percentage gain in more than a month.
The pharmaceutical sector tumbled 1.6 percent and was the worst performer on the board, after Eisai Co dived more than 16 percent on news an Alzheimer drug it is jointly developing failed to meet its mid-stage trial goals.
Santen Pharmaceutical stumbled 13.5 percent after it said on Thursday that the U.S. regulator's response to its application for intravitreal sirolimus indicated it would not be able approve the application in its present form.
Kobe Steel Ltd dropped more than 2 percent after the company admitted for the first time that executives were aware of the cheating, and reassigned three senior officials.
Outperforming the market were trading houses, with Itochu Corp rising 1.6 percent and Sumitomo Corp gaining 1.3 percent.
The broader Topix rose 0.3 percent to 1,827.35.
(Reporting by Ayai Tomisawa; Editing by Sam Holmes)