NEW YORK (Reuters Health) - Adults with chronic hepatitis C virus infection who respond quickly to treatment with a combination of two approved drugs --- peginterferon alfa-2a (Pegasys) and ribavirin (Copegus) -- may have a good chance of achieving long-term treatment success with a shortened course of therapy, according to research presented at the 57th annual meeting of the American Association for the Study of Liver Diseases in Boston.

Hepatitis C is the most common chronic blood-borne infection and is transmitted primarily by exposure to infected blood (sharing needles) or blood products. The disease chronically affects 170 million people worldwide and can cause cirrhosis, liver cancer and liver failure. Hepatitis C is the top reason for liver transplants in the United States.

Pegasys, given as a once-weekly injection, reduces the amount of virus in the blood, while Copegus, an oral pill taken twice daily, works by slowing down the growth of the virus.

In the just-reported study, investigators found that three quarters of a group of patients infected with hepatitis C genotypes 1 and 4, which are notoriously difficult to treat, who mounted a rapid response, had no detectable virus in blood after four weeks of treatment and were successfully treated after just 24 weeks on the combination regimen.

Patients with hepatitis C types 1 and 4 usually need 48 weeks of treatment.

These results show that within a month of starting therapy with this standard combination therapy, "we can give excellent news to some patients with difficult-to-treat genotypes - that they are likely to achieve treatment success with six months of therapy rather than 11 months," Dr. Donald Jensen, director of the center for liver diseases at the University of Chicago Hospital said in a statement.

"If confirmed in further study, these data are encouraging because they could help motivate patients to seek treatment and to stay on treatment," Jensen added.

The results of another study with 188 subjects presented at the conference show that intensifying treatment with higher-than-standard doses of Pegasys and Copegus may yield higher response rates in patients with a combination of three factors that make hepatitis C difficult to treat -- namely, being infected with genotype 1, having high levels of virus in the blood, and being overweight.

In the study, patients who got the intensified treatment achieved the highest rate of sustained response versus patients who got the standard regimen (47 percent vs 28 percent).

However, the use of higher doses of Pegasys and Copegus was associated with more serious side effects, such as anemia, as well as higher rates of premature withdrawal of therapy for safety reasons, compared with those on the standard dose.