Achillion Pharmaceuticals, Inc. is a biopharmaceutical company. The Company's primary business is to discover, develop and commercialize small molecule therapeutics for the treatment of infectious diseases and immune system disorders. The Company is focused on its complement inhibitor platform, directed at advancing small molecule compounds that have the potential to be used in the treatment of immune-related diseases associated with the complement system. The complement system is part of the body's immune system. The Company has initiated a first-in-human Phase I clinical trial for its first complement factor D inhibitor, ACH-4471, to assess safety, tolerability, pharmacokinetics, or PK, and pharmacodynamics, or PD. The Company has developed a portfolio of drug candidates, including odalasvir, ACH-3422 and sovaprevir.