May 9, 2007

Achillion Reports First Quarter 2007 Financial Results

NEW HAVEN, Conn., May 9, 2007 /PRNewswire-FirstCall via COMTEX News Network/ -- Achillion Pharmaceuticals, Inc., (Nasdaq: ACHN) a leader in the discovery and development of small molecule drugs to combat the most challenging infectious diseases, today reported financial results for the quarter ended March 31, 2007.

For the first quarter of 2007, the Company reported a net loss of $7.7 million, compared to a net loss of $5.3 million in the first quarter of 2006. Cash and cash equivalents and marketable securities at March 31, 2007 were $54.9 million.

"This quarter, we presented key data at the European Association for the Study of the Liver meeting validating the antiviral activity of the NS4A antagonism mechanism in HCV-infected patients," said Michael Kishbauch, President and Chief Executive Officer of Achillion. "Although we and Gilead elected to discontinue development of our first NS4A antagonist due to an undesirable impact on kidney function, its impressive antiviral activity validates NS4A as a new way of targeting HCV. Achillion is continuing its efforts with Gilead to assess the properties of additional compounds with this same promising mechanism of action, and plans to nominate one of a narrow set of potential candidates in the near term."

Kishbauch continued, "Achillion also marked this quarter with the continued clinical progress of elvucitabine, by completing enrollment of a Phase 2 combination trial with the drug candidate in treatment-naive HIV patients. We expect to announce top-line results from this trial on elvucitabine's safety, antiviral efficacy and pharmacokinetics in the next few months. We also continue to enroll patients in another Phase 2 trial in treatment-experienced patients, and hope to report data from that trial later this year. We plan on presenting the full results from both of these Phase 2 trials at a future medical meeting."

First Quarter 2007 Results

The Company reported a net loss attributable to common stockholders of $7.7 million for the three months ended March 31, 2007, compared to a net loss attributable to common stockholders of $6.4 million for the three months ended March 31, 2006. Total revenues were $1.6 million for the first quarter of 2007, compared to $2.2 million in revenue for the first quarter of 2006.

Research and development expenses were $8.4 million in the first quarter of 2007, compared to $6.2 million for the same period of 2006. Research and development expenses were primarily related to our Phase 2 clinical trials of elvucitabine, a Phase 1b/2 clinical trial of our first NS4A antagonist for HCV, late-stage discovery efforts in collaboration with Gilead to pursue next- generation candidates for potential development in HCV, and continued preclinical advancement of ACH-702, our antibacterial candidate.

For the three months ended March 31, 2007, general and administrative expenses totaled $1.5 million, compared to $1.2 million for the same period in 2006.

About Achillion

Achillion is an innovative pharmaceutical company dedicated to bringing important new treatments to patients with infectious disease. The company's proven discovery and development teams have advanced multiple product candidates with novel mechanisms of action. Achillion is focused on solutions for the most challenging problems in infectious disease - HIV, hepatitis and resistant bacterial infections. For more information on Achillion Pharmaceuticals, please visit the company's web site at or call Achillion at 1-203-624-7000. ACHN-G

This press release includes forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 that are subject to risks, uncertainties and other factors, including statements with respect to Achillion's ability to discover and develop drug candidates and the nomination of a new NS4A antagonist candidate. Among the factors that could cause actual results to differ materially from those indicated by such forward-looking statements are: unexpected regulatory actions or delays; uncertainties relating to results of clinical trials, including additional data relating to ongoing clinical trials; Achillion's ability to obtain additional funding required to conduct its research, development and commercialization activities and Achillion's dependence on its collaboration with Gilead Sciences. These and other risks are described in the reports filed by Achillion with the U.S. Securities and Exchange Commission, including its Annual Report on Form 10-K for the year ended December 31, 2006.

All forward-looking statements reflect Achillion's expectations only as of the date of this release and should not be relied upon as reflecting Achillion's views, expectations or beliefs at any date subsequent to the date of this release. Achillion anticipates that subsequent events and developments may cause these views, expectations and beliefs to change. However, while Achillion may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so.

    Mary Kay Fenton
    Achillion Pharmaceuticals, Inc.
    Tel. (203) 624-7000

    Kari Watson
    MacDougall Biomedical Communications, Inc.
    Tel. (508) 647-0209

    Statements of Operations
    (Unaudited, in thousands, except per share amounts)

                                                       Three Months Ended
                                                            March 31,

                                                      2007              2006

    Revenue                                         $1,550            $2,151

    Operating expenses:
      Research and development                       8,367             6,187
      General and administrative                     1,548             1,219

        Total operating expenses                     9,915             7,406

    Loss from operations                            (8,365)           (5,255)

    Other income (expense):
      Interest income                                  759                72
      Interest expense                                (265)             (189)
      Tax benefit                                      201                25

        Total other income (expense) -net              695               (92)

    Net loss                                        (7,670)           (5,347)

    Preferred stock dividends and
     accretion                                         -              (1,028)

    Net loss attributable to common
     stockholders                                  $(7,670)          $(6,375)

    Net loss attributable to common
     stockholders per share
     - basic and diluted                            $(0.49)          $(12.52)

    Weighted average shares outstanding
    - basic and diluted                             15,540               509

    Balance Sheets
    (Unaudited, in thousands)

                                             March 31,         March 31,
                                               2007              2006

    Cash and cash equivalents and
     marketable securities                    $54,942           $62,566
    Working capital                            44,324            53,190
    Total assets                               59,447            67,146
    Long-term liabilities                       6,200             8,102
    Total liabilities                          19,139            19,776
    Total stockholders' (deficit) equity       40,308            47,370

SOURCE Achillion Pharmaceuticals, Inc.

Mary Kay Fenton of Achillion Pharmaceuticals, Inc., +1-203-624-7000,; or Media, Kari Watson of MacDougall Biomedical Communications,
Inc., +1-508-647-0209,, for Achillion Pharmaceuticals, Inc.

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