X0203 3 2010-08-20 0 0001070336 ACHILLION PHARMACEUTICALS INC ACHN 0001024000 BLAIR JAMES C C/O DOMAIN ASSOCIATES, LLC ONE PALMER SQUARE PRINCETON NJ 08542 0 0 1 0 Common Stock 7972968 I By Domain Partners VIII, L.P. Common Stock 59161 I By DP VIII Associates, L.P. Warrants to Purchase Common Stock 3.1125 2010-08-20 2017-08-20 Common Stock 2790539 I By Domain Partners VIII, L.P. Warrants to Purchase Common Stock 3.1125 2010-08-20 2017-08-20 Common Stock 20706 I By DP VIII Associates, L.P. The Reporting Person is a Managing Member of One Palmer Square Associates VIII, LLC, which is the sole general partner of Domain Partners VIII, L.P. and DP VIII Associates, L.P. Pursuant to Instruction (5)(b)(iv) of Form 3, the Reporting Person has elected to report as indirectly beneficially owned the entire number of securities beneficially owned by each such entity. The Reporting Person disclaims beneficial ownership of any securities, and any proceeds thereof, that exceed his or her pecuniary interest therein and/or that are not actually distributed to him or her. /s/ Kathleen K. Schoemaker, Attorney-in-Fact 2010-08-20