Shares of Eton Pharmaceuticals Inc. tumbled 20.0% in premarket trading on Friday after the company said the Food and Drug Administration issued a complete response letter, saying it cannot approve Eton’s application for its methanol poisoning treatment in his current form. Eton said it can address most of the questions raised by the FDA “in the coming months.” Eton’s stock is up 4.4% for the year, while the broader S&P 500 has gained 11.8%.

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