Schering-Plough's Phase II data for boceprevir put the protease inhibitor for hepatitis C virus in a stronger position against Phase III telaprevir from Vertex, but the edge pertains mainly to HCV cases that require dosing four times longer, with more patients dropping out because of adverse events.

An interim analysis disclosed by Schering-Plough Aug. 4 showed that after 48 weeks of treatment, 74 percent of treatment-naïve patients given boceprevir combined with PegIntron (pegylated interferon alfa-2b) and Rebetol (ribavirin) achieved undetectable HCV over a sustained period, compared with 38 percent of patients who got only PegIntron and Rebetol.

The 595-patient trial, known as SPRINT-1, included four weeks of lead-in with PegIntron and Rebetol alone and the sustained viral load was measured at 12 weeks. Sixty-six percent of patients not given the lead-in had their HCV knocked out by boceprevir.

Toxicity, though, apparently built up over the longer treatment period, with 19 percent of patients dropping out because of fatigue, anemia, nausea and headache. In the trial's control arm, only 8 percent quit.

In May, Schering-Plough made known its plans for Phase III trials with boceprevir (¹ Also see "Schering-Plough Lays Out Phase III Plan For HCV Therapy Boceprevir" - Pink Sheet, 21 May, 2008.). Vertex's drug and boceprevir lead the pack in an increasingly hot protease-inhibitor HCV war (² Also see "Protease Inhibitors Line Up To Challenge Vertex In HCV" - Pink Sheet, 18 March, 2008.).

Leerink Swann analyst Howard Liang conceded in an Aug. 5 research note that boceprevir's results appear strong, but "not necessarily better than telaprevir," which has been shown to excel in HCV treatment non-responders.

"Fundamentally, the big picture remains that telaprevir appears to be a more potent agent, but boceprevir has shown an ability to be dosed for a longer period," Liang wrote.

Telaprevir patients tend to respond sooner than those on boceprevir, which could mean a shorter treatment period, Liang pointed out. Clinicians will argue over whether the benefits of longer therapy outweigh the drawbacks.

Vernon Bernardino, analyst with Rodman & Renshaw, in an Aug. 4 note, called the results for boceprevir an "incremental positive" for Schering-Plough that does not change telaprevir's advantage.

Bernstein analyst Geoff Porges wrote in a note the same day that boceprevir is likely to be used only by patients who cannot tolerate the rash that telaprevir often brings as a side effect.

"Given the limitations of boceprevir for prior treatment-failure patients (lack of efficacy in clinical trials so far), Schering's drug has substantially lower revenue potential that Vertex's," according to Porges.

- Randall Osborne (r.osborne@elsevier.com)

Length Of Therapy Becomes An Issue In HCV Protease Inhibitor Race

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