UPDATE 1-Shire gets mixed FDA response on Pentasa

* Pentasa could face generic competition

* FDA ruling a minor negative for Shire - analyst

(Adds details, analyst comment)

LONDON, Aug 24 (Reuters) - British drugmaker Shire Plc SHP.L could face competition from a generic version of its gastrointestinal drug Pentasa after a ruling from U.S. regulators.

The U.S. Food and Drug Administration gave a mixed response to the company’s request for formal guidance on what generic versions of Pentasa must prove, denying its request that comparative clinical endpoint studies be used.

However, other aspects of Shire’s citizen’s petition were granted, the company said on Tuesday.

Pentasa could face generic competition in the near future as a result of the ruling, said Jefferies International in a note.

“This represents a minor negative for Shire, in our view, as Pentasa is relatively mature and generic erosion could still be relatively slow,” the broker said.

Shares in Shire Plc closed at 1,418 pence ($21.83), shortly before the announcement.

(Reporting by Julie Crust; editing by Rosalba O’Brien)

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