Peginterferon alfa-2a (Pegasys, Roche Products) has a UK marketing authorisation for 'the treatment of chronic hepatitis C in adult patients who are positive for serum HCV-RNA, including patients with compensated cirrhosis and/or who are co-infected with clinically stable HIV'. The preferred treatment regimen is in combination with ribavirin, but monotherapy is indicated in cases of intolerance or contraindication to ribavirin. Patients may not have been previously treated or their condition may have not responded to previous treatment with interferon alfa (pegylated or non-pegylated) alone or in combination with ribavirin. The recommended dose is 180 micrograms once a week, administered subcutaneously, for 16, 24 or 48 weeks depending on HCV genotype, baseline viral load and response to treatment. The recommended duration of peginterferon alfa-2a monotherapy is 48 weeks.