Mylan spokesman Nina Devlin, when asked by CNBC if that was the first time the company had ever revealed a projection of market size for the generic version, said she believed it was.
EpiPens contain the drug epinephrine, which counteracts the potentially fatal allergic reaction known as anaphylaxis.
Grassley on Thursday said of Mylan's letter, "I appreciate the information provided but it's an incomplete response and wouldn't satisfy my constituents who are upset about the EpiPen price increases. It doesn't provide the full picture that I requested, and it doesn't answer all of my questions."
"There isn't much discussion of what analyses went into the price-setting in response to my question," Grassley said. "There also isn't much of a description of the product features and value that the company says have helped to justify the price increases. The company say a large number of patients have benefited from patient assistance programs but the outrage Congress is hearing seems to indicate that a lot of people aren't seeing those benefits. It may be that the newly announced expanded patient assistance program will make a difference, but that's to be determined. consumers."