(Reuters) -Amgen ( AMGN ) shares jumped 14% premarket on Friday after the U.S. drugmaker hinted at encouraging interim trial data on its experimental obesity drug, denting rival stocks such as Novo Nordisk but leaving analysts frustrated over a lack of details.

The company is conducting mid-stage studies of the injectable drug and said that, based on interim data, it was "confident in MariTide's differentiated profile and believe it will address important unmet medical needs".

"The fact that ... the delivery dosing schedule is likely to be monthly or less frequent implies far fewer injection devices than competitors who, for example, are administering a weekly therapy," Amgen ( AMGN ) CEO Robert Bradway told investors late on Thursday.

Amgen ( AMGN ), however, provided no specifics on the actual data, and said it plans to start a late-stage study later this year.

Mizuho analyst Salim Syed said he acknowledged "the seemingly more upbeat tone" on the drug franchise but "we'd argue that a lot of questions remain unanswered."

Those questions, said Syed, included manufacturing plans, given that rivals Eli Lilly ( LLY ) and Novo Nordisk are racing to boost supply, and Amgen ( AMGN ) plans to make headway in the commercial market.

Supply of powerful new weight-loss drugs from Lilly and Novo are already falling short of soaring demand, and several other drugmakers are gunning to grab a share of the market that some analysts expect will reach $100 billion by the end of the decade.

Amgen's ( AMGN ) comments pulled down shares of rivals on Friday. Eli Lilly ( LLY ) was down 2.6%, while Novo Nordisk's Denmark-traded shares fell 4.4%, on track for their biggest one-day fall since August 2022.

"Novo's share price today is certainly factoring in some negative reaction to Amgen's ( AMGN ) positive commentary on MariTide development yesterday," Kepler Cheuvreux analyst David Evans said.

Novo's Thursday comments on cutting prices of its Wegovy weight-loss treatment also weighed on its shares, Evans said.

Shares of smaller weight-loss drug developer, Viking Therapeutics, fell 6% premarket.

Amgen's ( AMGN ) shares, part of the bluechip Dow Jones index, rose 14.1% to $317.65 in premarket trading.

The company's stock is trading 13.9 times its forward 12-month earnings estimates, compared with a forward price-to-earnings ratio of 34.2 for Novo Nordisk and 48.49 for Eli Lilly ( LLY ).

(Reporting by Manas Mishra and Christy Santhosh in Bengaluru and Elviira Luoma in Gdansk; Editing by Sonia Cheema and Devika Syamnath)