Symmetrel was the first synthetic antiviral drug developed in the United States, and marked DuPont’s entry into pharmaceuticals. In 1957 scientists at the Stine Laboratory began screening substances for their antiviral properties, and by 1964 amantadine hydrochloride had proven most effective.
DuPont could not patent the well-known substance itself but could patent its use in treating upper respiratory infections. In 1966 the Food and Drug Administration (FDA) approved Symmetrel as an oral drug in syrup or tablet form, but limited its use to the treatment of a particular strain, the Asian flu. The next year DuPont began marketing Symmetrel and seeking FDA approval to broaden its uses. The Centers for Disease Control (CDC) finally helped DuPont secure approval of Symmetrel to combat all A-type strains of influenza. But sales of Symmetrel remained limited because influenza was a seasonal disease and it was effective only if taken within 48 hours of the onset of symptoms. Sales improved during the 1980s and 1990s, but not enough to support brand marketing and by 2000 DuPont was selling the drug only in its generic form, “amantadine.”