The combination includes Intron-A, which Schering-Plough already sells alone to treat hepatitis, and ICN's drug ribavirin, or Rebetol.
Studies have shown the two drugs together provide a significant benefit to patients. Schering will sell the combination in a single package containing the Rebetol pills and injections of Intron-A, under the name Rebetron.
"This combination should be seriously considered by practitioners in this field," said Judith Feinberg, an associate professor in the division of infectious diseases at the University of Cincinnati Medical Center and a member of the FDA advisory panel that recommended approval of the drug last month.
Shares of Madison, N.J.-based Schering-Plough rose $1.88 to $84.88 Wednesday, while shares of Costa Mesa-based ICN were up 81 cents to $42.50.
The approval was expected because the FDA advisory panel backed the combination therapy after hearing that patients who take it increase tenfold their chances of beating back the virus. At the time, panel members said the combination is the first hepatitis treatment to present hope for a cure.
Pregnant women shouldn't take the drug combination, the FDA said. Indeed, the drugs will have a so-called black box warning, a specially highlighted message to doctors and patients, about the drugs' possibility of inducing birth defects in the children of patients, the agency said.
Sales of the drug will take time to grow, analysts said, because patients who have gone through treatment only to suffer relapses may be reluctant to face side effects again, analysts said.
"Initially, I think it is going to take a bit of selling to get this drug moving. It's not a cakewalk," said James Keeney, an analyst with ABN Amro. "After time, this will build."
There's a lot of room for better treatments for hepatitis C, analysts said at the time of the panel hearing. Only about 100,000 patients are taking Schering's Intron-A alone to treat their hepatitis, according to Prem Lachman, a partner at the Galleon Group and a former analyst at Goldman Sachs.
"It's clearly not tapping into the 4 million that have been infected or even the 1 million that have been infected from transmission," he said.
Schering is readying an application for use of the drug as a first-line treatment in hepatitis C patients, which would leave it well-positioned as more and more patients discover they have the disease. The company plans to file the application with the FDA by the end of the year.
ICN will receive royalties on the combination regimen, which will be marketed by Schering-Plough. Investor interest in the therapy has helped ICN's stock triple in value in the past year.
ICN currently sells its drug in another form, under the brand name Virazole, for treating respiratory infections.
The combination Schering-ICN therapy has drawbacks. Intron-A is already a hard drug to take, with injections often causing flulike symptoms. The combination adds the side effects of a regimen of pills on top of that.
Hepatitis C has recently generated much attention as scientists learn more about the condition, first identified in 1989. Experts now estimate that almost 4 million Americans are infected with hepatitis C, a virus most often transmitted through contaminated needles or a tainted blood transfusion before screening tests were available. Sometimes, the disease appears in patients with no risk factors.
The government is beginning a process of notifying Americans who may have been exposed to the virus through a transfusion, Lachman said, and the drug combination is being tested to see how effective it is as a first treatment for hepatitis.
Hepatitis C can cause severe liver problems, including cirrhosis, in about 20% of those infected. Others may lead a full life with few problems.
To date, there's no cure for the condition, and many patients fail to derive long-term benefit from available treatments.
Amgen Inc. and Roche Holding are among the other makers of hepatitis C treatments.