Altimmune's obesity drug safety concerns shrink shares

March 21 (Reuters) - Altimmune Inc's (ALT.O) experimental obesity drug helped reduce weight by over 10% on average in a mid-stage trial, the company said on Tuesday, but safety concerns sent its shares tumbling more than 50%.

Most patients experienced nausea and vomiting of mild and moderate severity, with one patient requiring rehydration after experiencing severe side effects, the company said, adding the study did not allow for dose reduction.

"Weight loss that they showed today is kind of right at the border of what investors thought was going to be acceptable. So it's not enough for some, it's just barely enough for others," said JMP Securities analyst Jonathan Wolleben.

Wolleben added that the drug showed " a little bit worse" tolerability than previous data.

Patients who received a 2.4 milligram dose of Altimmune's experimental drug, pemvidutide, achieved average weight loss of 10.7% at the end of week 24, the company said.

The data looked competitive to mid-stage data from Novo Nordisk's (NOVOb.CO) obesity drug Wegovy and Eli Lilly's (LLY.N) candidate for the condition, most analysts said.

In all, 24% of those receiving Altimmune's experimental treatment chose to discontinue - half of which were due to side effects - compared with 28.2% for those on a placebo, the company said.

The adverse event-related discontinuation "could be mitigated" once reduced doses are allowed to be given to trial patients, Altimmune's Chief Medical Officer Scott Harris said on a conference call.

Pemvidutide's side effects were similar to those seen in other drugs being developed or already approved for obesity. Novo Nordisk's (NOVOb.CO) Wegovy and Eli Lilly's (LLY.N) drug, chemically known as tirzepatide, both showed common side effects of nausea and vomiting in their late-stage studies.

Altimmune is targeting a global obesity treatment market that is expected to hit $50 billion in sales by 2030. While Novo Nordisk's drug Wegovy is already available, Lilly expects approval for its obesity drug candidate, tirzepatide, this year.

Shares of Maryland-based Altimmune were down 54% at $4.99.

Reporting by Sriparna Roy and Bhanvi Satija in Bengaluru; Editing by Savio D'Souza and Sriraj Kalluvila

Our Standards: The Thomson Reuters Trust Principles.

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Bhanvi Satija reports on pharmaceutical companies and the healthcare industry in the United States. She has a postgraduate degree in International Journalism from City, University of London.

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Sriparna reports on pharmaceutical companies and healthcare in the United States. She has a master's degree in English literature and post graduate diploma in broadcast journalism.