In 1994, Rimantadine, derived from amantadine, was approved by the FDA to treat influenza A in 1994. Rimantadine was approved in 1993 for treatment and prophylaxis in adults, but was approved only for prophylaxis in children. In 2009, 100% of seasonal H3N2 and pandemic flu samples tested had resistance to rimantadine and it is no longer recommended for treatment of the flu.