Vertex's drug for treating hepatitis C virus, Incivek (telaprevir), is on course to smash the previous record for the biggest revenue-generating drug launch ever, says an analyst firm.

The direct-acting antiviral generated $494.1 million in sales from its US launch in May through the end of September, Vertex disclosed recently in an earnings report. The EU approved the med, branded as Incivo, during the third quarter, as did Canada and Japan. With launches in all those markets under way through the fourth quarter, Incivek should reach a billion dollars in sales by year's end, Wolters Kluwer inThought analyst Julie Hoggatt wrote in a research note yesterday.

Assuming Incivek goes blockbuster in under nine months, that would be half the time it took for Genentech cancer med Avastin to reach the same sales level after approval in 2004, Hoggatt pointed out. Abbott's RA injection Humira and Merck diabetes pill Januvia took about two years to earn blockbuster status, after those drugs reached market in 2002 and 2006, respectively.

Rival hep. C antiviral Victrelis, which was approved a week before Incivek, is moving along a slower adoption curve. Merck reported sales through September of only $53 million for Victrelis. On a prescription basis, Incivek is consistently averaging 1,000 new scripts (NRx) per week, compared to 300/week for Victrelis—a 3:1 average NRx ratio, not including refills.

Based on the most recent quarterly numbers, Wolters Kluwer raised its Incivek revenue forecast to $1.0 billion in 2011 and $1.4 billion in 2012, and lowered its Victrelis estimate to $100 million in 2011 and $256 million for 2012.

Incivek is clearly winning the market share battle. The question now becomes, how will it sustain sales?

That will depend on the size of the remaining pool of untreated hep. C patients, Hoggatt wrote. Weekly new prescription counts for the two drugs are “consistent but not growing” over the last several weeks, suggesting that sales will plateau in 2012 for both drugs, she predicted. (IMS Health data suggesting Incivek TRx were flat in late September were due to a data supply issue, IMS said.) All-oral hep. C regimens, expected to arrive in 2014 at the earliest, will be another cap on Incivek/Victrelis sales.

But near term, there's still some room for sales growth. Both new protease inhibitors are used in combination with ribavirin and with pegylated interferons, either Merck's own PegIntron or Roche's Pegasys, which is the market leader. The number of unique doctors prescribing Incivek in September was half the number of unique writers of Pegasys, Wolters Kluwer data show. That bodes well for the Vertex brand, assuming Pegasys represents a ceiling, of sorts, for the number of prescribers and scripts written per doctor.

Moreover, both the number of Incivek-writing physicians (2,061 as of September) and the average number of Incivek scripts per doctor (3.7, vs. 2.7 per prescriber of Victrelis) suggest that Vertex's drug is being written by half of the clinicians who are likely to prescribe it, and that those docs are already using it for nearly as many of their patients as they are prescribing Pegasys. As new prescribers (55-60% of scripts for all these agents are written by gastroenterologists) come on board, older ones probably won't go to the Rx pad as often.

Incidentally, Wolters Kluwer predicts that the first of the all-oral HCV regimens—which are being designed to avoid injected intereferon—won't reach market until 2015. Companies testing these regimens include Abbott, Roche, Pharmasset, Boehringer Ingelheim, Bristol-Myers Squibb and Gilead. Vertex recently experienced a setback with is own all-oral attempt but it and Merck may still pursue the approach.