The world's biggest insulin producer said it could be forced to drop haemophilia drug candidate, vatreptacoq alfa, unless phase III data proved very favorable.

Drugs are classed as blockbusters if they reach annual sales above $1 billion within five years of launch.

"Unless we get really good clinical results, and we will know in October if we do, we will have to drop the studies," Novo's Chief Scientific Officer Mads Krogsgaard told Reuters in an interview.

The group is searching for replacements for Novoseven, which ran off patent protection in the United States in 2010 and in Europe last year. It has another four haemophilia drug candidates in phase III studies.

The global haemophilia drugs market is worth about 43 billion crowns ($7.65 billion), and is growing by about 5-6 percent per year, Novo Nordisk says.

The group's sale of Novoseven rose by 15 percent in the second quarter of the year to 2.45 billion compared with the same quarter last year.

Krogsgaard also said stiff insulin competition from rival Sanofi had reduced Novo Nordisk's market share in Japan to below 60 percent from around 70 percent previously.

The group's Levemir insulin has lost out to Sanofi's Lantus, but Novo Nordisk would start turning the tables with the launch of Tresiba, also known as degludec, once it got approval, which is expected in the second half of the year, Krogsgaard said.

The company's sale in Japan and Korea combined rose 21 percent in the second quarter to 1.7 billion crowns out of total group sales of 19.47 billion crowns.

(Editing by David Cowell)

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