* FDA demands extra work, large safety study for asthma drug
* Says looking for viable way forward in United States
* Shares down 15 pct
(Adds further details, share price)
LONDON, June 24 (Reuters) - Britain's SkyePharma (SKP.L) said on Thursday the U.S regulator has set tougher than expected demands for approval of its asthma drug Flutiform, which may prove insurmountable.
The U.S. Food and Drug Administration (FDA) refused approval for Flutiform in January, resulting in its U.S. partner Abbott (ABT.N) handing over control of the U.S application to SkyePharma.
SkyePharma's shares, which have halved since the refusal, were down 15 percent at a 21-month low of 28 pence by 1214 GMT, after SkyePharma received more information on the FDA's rejection and subsequent conditions for seeking approval.
The firm said the FDA's requirements for approving Flutiform had materially changed during the course of the development programme and meeting the requirements would involve significant additional work, including a large post-approval safety study. "The company is working with its advisors to review all of the options available to it with a view to determining whether there is a viable way forward for Flutiform in the United States," it said in a statement on Thursday.
SkyePharma, a drug delivery specialist, said it was continuing with the process of filing for Flutiform approval in Europe, and progress continued with its development in Japan.
The inhaled drug, which is being developed for the treatment of asthma and chronic obstructive pulmonary disease, if approved would compete with GlaxoSmithKline's (GSK.L) market-leading Advair and AstraZeneca's (AZN.L) Symbicort. (Reporting by Paul Sandle; Editing by Greg Mahlich)