Shares in Rigel took a downward turn after its experimental asthma drug failed to hit targets in a mid-stage trial.

The US group's stock was trading down nearly 20% at one point yesterday as investors shrank back on the news, which signals the end of the drug's development for allergic asthma.

The Phase II trial showed the inhaled SYK inhibitor R343 to be "relatively safe and well tolerated" at both doses tested, but failed to meet both its primary (change in lung function) secondary endpoints.

The findings have come as somewhat of a shock to the firm. 

"This was not the result we expected based on the collection of data we had previously seen with R343 in this therapeutic area," said James Gower, Rigel's chairman and chief executive.

Others agree; Reuters cited Leerink Swann analyst Marko Kozul as noting surprise "after Phase I data demonstrated that R343 attenuates both the early and long acting response, which encompasses the full spectrum of current therapies."

Rigel recently suffered another blow when AstraZeneca announced in June that it would not be filing its rheumatoid arthritis drug fostamatinib (licensed from Rigel in 2010) because of mediocre data, thereby snatching away the chance of up to $345 million in milestone payments and $800 million in other sales-based royalties from the firm.