- Kawasaki Kisen Kaisha, up 5.38%, was the biggest gainer on Nikkei, followed by Daiichi Sankyo.
TOKYO: Japan's stock index Nikkei changed course and inched down on Tuesday, as losses in market heavyweights offset gains in drugmakers after Eisai Co's Alzheimer drug received US nod.
Nikkei share average inched down 0.11% to 28,987.58 by 0235 GMT, while the broader Topix edged up 0.06% to 1,962.07.
"The news on Eisai has given a boost to its peers as well as the overall market," said Shoichi Arisawa, general manager of the investment research department at IwaiCosmo Securities.
"Investors are also scooping up Japanese shares which lagged behind their global peers as prospects of an economic recovery has brightened amid a rollout of COVID-19 vaccines."
But Nikkei's earlier gains were snapped as investors were cautious ahead of the US consumer price index (CPI) report this week and the US central bank's meeting next week, market participants said.
US regulators on Monday approved a drug jointly developed by Eisai and Biogen Inc's as the first treatment to attack a likely cause of Alzheimer's disease.
Drug makers were the top gainers among the Tokyo Stock Exchange's 33 industry subindexes, with Eisai remaining untraded as buy orders far exceeded sell orders.
Daiichi Sankyo jumped 4.58% and Astellas Pharma rose 1.83%.
Losses in index heavyweights, however, weighed on the markets, with global start-up investor SoftBank Group down 1.56% and air-conditioner maker Daikin Industries losing 2.9%.
Kawasaki Kisen Kaisha, up 5.38%, was the biggest gainer on Nikkei, followed by Daiichi Sankyo.
Sumitomo Metal Mining , down 3.41%, was the largest decliner on the index, followed by Oji Holdings losing 2.37% and Daikin Industries.
There were 130 advancers on the Nikkei index against 86 decliners.