The first two, closely related antivirals - Amantadine and Rimantadine - held great promise. They targeted the M2 protein on the membrane of the Type A flu virus, interfered with viral replication and shortened a case of flu by one to two days. Amantandine and Rimantadine have not caught on as popular treatments, however. Both antivirals have troublesome side effects; nausea, anorexia, and impairment of the central nervous system, resulting in insomnia, nervousness and dizziness. In addition, they don't affect Type B virus, because it lacks the target M2 protein.¹¹⁸