On the surface, Idenix Pharmaceuticals' (Nasdaq: IDIX) hepatitis C data looks pretty good. A solid 100% of patients taking the high dose of its nucleotide inhibitor IDX184, and 80% of the patients taking the low dose of the drug, were rid of the virus four weeks after treatment was completed. Combine those for an 89% early cure rate.

Dig a little deeper and you'll see there's a little more to the story.

First, between both doses, there are only nine patients. Hepatitis C drugs tend to perform fairly consistently as trials progress, so solid early data shouldn't be dismissed. With just nine patients, though, it isn't clear whether the data will be closer to 80% -- a ho-hum result -- or 100%, which would obviously be very competitive.

More important, those nine patients were from a subset of patients that responded well to the initial treatment with a combination of IDX184, pegylated interferon, and ribavirin. Of the 31 patients that entered the trial, only 18 had undetectable virus levels four weeks and 12 weeks after treatment. Nine of those patients were given 12 additional weeks of pegylated interferon and ribavirin, which is the interim data we have now. The other nine were given the combo for an additional 36 weeks.

Presumably those patients that stay on the drugs for 36 weeks will perform as well or better than those that were given the drugs for just 12 weeks. But what about the 13 patients that weren't randomized to get either 12 or 36 weeks of additional treatment? One achieved a quick response like the other 18, but dropped out of the study before the randomization began. The other 12 didn't achieve a quick response and were put on the longer 36-week treatment, so it isn't known how many will eventually come up positive. Keep in mind that group represents 40% of those known to still be enrolled in the trial, which could drag down the overall cure rate.

Not that the combo of IDX184, pegylated interferon, and ribavirin will ever see the light of day. Pegylated interferons -- Roche's Pegasys and Merck's (NYSE: MRK) PegIntron -- have to be injected and have nasty side effects. Idenix ran this trial simply to gauge IDX184's efficacy, which seems fairly good for now, but it'll need to combine it with (an)other oral drug(s) to compete with all oral regimens being developed by Gilead Sciences (Nasdaq: GILD), Bristol-Myers Squibb (NYSE: BMY), Abbott Labs (NYSE: ABT), and others.

Which drug(s)? Management didn't say.

It likely depends on who owns IDX184. If Bristol's BMS-986094, which it got from the acquisition of Inhibitex, is a failure -- hints of that here -- the pharma might be interested in picking up IDX184 to combine with its daclatasvir, which has already been shown to work well with Gilead's nucleotide inhibitor.

If Idenix has to go it alone, the biotech has an NS5A inhibitor, same class as daclatasvir, a little behind IDX184. That seems like a less than ideal scenario for investors, but certainly an option if no one is interested in picking up IDX184 or the whole company.

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