Sarepta shares rose 15.55% to $149.93.
Baird analyst Brian Skorney said in a note that "Pfizer fell way short on both safety and efficacy" for a gene therapy drug for a genetic degenerative disorder affecting 1 in 3,500 to 5,000 men. "It [the drug] just did not look safe," Skorney added.
Sarepta is making a competing drug, called Exondys 51, and has been gaining market share in the space for such types of drugs, according to RBC Capital Markets analysts.
Pfizer mentioned what some of the drug's safety concerns were in a press release Friday.
"Preliminary safety results show that the most common adverse events suspected to be related to PF-06939926 are nausea, vomiting, decreased appetite, tiredness and/or fever, which were reported within a few days of dosing by 4 of 6 study participants," the company said.
Pfizer shares were down 0.18% to $43.34.
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