NEW YORK ( TheStreet) -- The midsummer implosion of Bristol-Myers Squibb's ( BMS) BMS-094 (formerly INX-189) and subsequent FDA clinical hold for Idenix Pharmaceuticals' ( IDIX) IDX-184 and IDX-19368 has winnowed the field of late-stage hepatitis C drug candidates. Given these shifting dynamics, the outlook for Achillion Pharmaceuticals' ( ACHN) hepatitis C drug pipeline has improved and the stock is a solid long idea for investors seeking exposure to the hepatitis C market. I haven't always been an Achillion fan. After attending the European Association for the Study of the Liver (EASL) meeting this spring, I gave Achillion a C-minus on my hepatitis C scorecard, largely due to indifference. I noted back then: Achillion has two NS5A inhibitors, ACH-3102 and ACH-2928, which look okay in early studies, but I'm not sure what makes these drug candidates stand out. I feel similarly unexcited about ACH-1625, a protease inhibitor, which looked decent in a confusing study that combined it with interferon and ribavirin. I'm just not convinced these are valuable assets, so I'm going to wait on the sidelines. I wasn't the only one confused by Achillion's Phase IIa study of ACH-1625, which is now known as sovaprevir. On the same day as my EASL review, the company issued a press release clarifying the results. Let's take another look. Sovaprevir (ACH-1625) Achillion's explanation for the uninspiring efficacy results in the EASL poster makes sense: Data included semi-compliant patients who were not consistently taking drug. In fact, viral loads for all 22 patients that completed treatment -- 12 weeks of sovaprevir combined with the immune boosters interferon and ribavirin, followed by 12 weeks of interferon and ribavirin alone -- reached undetectable levels. That's far more intriguing than the initially reported end-of-treatment response rates, which dipped as low as 69%. At a recent R&D day, management provided updated data from the same Phase IIa study: 78% (200 mg once-daily), 77% (400 mg), and 85% (800 mg) sovaprevir-treated patients achieved a sustained virologic response -- a reliable indicator of cure -- at 12 weeks (SVR12). Although that's somewhat less effective than other protease inhibitors in development, such as Abbott's ritonavir-boosted ABT-450 (88% SVR12) or Johnson & Johnson's TMC-435 (82% SVR12), it's good enough to make sovaprevir an attractive asset for combination therapy regimens. At the R&D day, Achillion also discussed sovaprevir's side effects in detail. At the highest dose tested (800 mg once-daily), one patient had significantly elevated liver enzymes and three patients (16%) had increased bilirubin levels. The combination of both elevated liver enzymes and bilirubin levels in patients raises concerns about Hy's Law, a reliable prognostic indicator for severe liver damage. This is the safety signal that worried me about sovaprevir at last spring's EASL meeting.