This time last year, I highlighted the warehousing of patients as the biggest obstacle that hepatitis C drugmakers should be worried about. It looks like it's coming to fruition.

U.S. sales of Vertex Pharmaceuticals' (NASDAQ:VRTX) Incivek took off like a rocket ship, hitting $457 million in the fourth quarter of 2011. The insane rise in sales was caused by a backlog of patients that put off treatment with Roche's Pegasys and Merck's (NYSE:MRK) PegIntron because their cure rates are pretty pathetic. Since hepatitis C is a slow progressing disease, doctors can afford to warehouse the patients until better treatments come along.

After that initial wave of patients that had been waiting for the drug, sales came crashing down. In the third quarter, Vertex sold $254 million worth of Incivek, 23% lower than last quarter and a whopping 44% off the peak sales. Vertex is sticking with its guidance of $1.1 billion to $1.25 billion in sales for all of 2012, which would put fourth quarter sales between $161 million and $311 million. Given the current path, I'd expect it to be at the lower end of that range.

What's bad news for Vertex, is good news for Gilead Sciences (NASDAQ:GILD) and Abbott Labs (NYSE:ABT); there should be a large number of patients available to treat once their cocktails are approved. But then what? Will there be another round of warehousing to wait for drugs from Idenix Pharmaceuticals (NASDAQ: IDIX), Achillion Pharmaceuticals (NASDAQ:ACHN), and others that might have better efficacy, safety and/or more convenient dosing? And further down the line, some patients will just wait until the drugs go off patent and cheap generics are available.

Investors therefore should really be concentrating on Vertex's cystic fibrosis program. Sales of Kalydeco were just $49 million in the third quarter, but the combination drugs it's developing will treat more patients, producing higher sales.

Vertex still has a blockbuster -- for now -- but the company will act a lot more like a development stage biotech over the next few years, trading up and down based on the phase 3 results from the cystic fibrosis drug-combo trials.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.