Influence of ribavirin on the dynamics of hepatitis C viremia in interferon-alpha-treated patients with response or nonresponse

Combination therapy with interferon-alpha (IFN alpha) plus Ribavirin has be en shown to improve the response rate in patients with chronic hepatitis C as compared to IFN alpha alone. However, the mode of anti-viral action of R ibavirin is still unknown. To prove, whether Ribavirin has any additional e ffect on the decline of hepatitis C viremia during the first weeks of treat ment patients with and without combination therapy were compared. Kinetic s tudies were performed in patients who either responded to IFN alpha alone o r IFN alpha plus Ribavirin combination as well as in nonresponders to both forms of therapeutic approaches. 64 IFN alpha naive patients with histologically proven chronic hepatitis C were included in the study. Patients were randomized to receive either IFN alpha -2a (Hoffmann-La Roche) 6 MU thrice weekly or IFN alpha 6 MU tiw plus Ribavirin (Meduna) 14 mg/kg/day for 12 weeks. 37 patients (58%) became HCV RNA-negative (= responders; 17 [46%] with IFN alpha alone, and 20 [54%] wi th combination therapy). 27 patients remained HCV RNA-positive (= non-respo nders; 13 [48%] with IFN alpha alone, and 14 [52%] with combination therapy ). HCV RNA concentrations were measured in all patients at baseline as well as 1, 2, 4, and 12 weeks after the start of treatment (bDNA assay, Chiron) . Using nonradioactive single-stranded conformation (SSCP)-analysis of the HCV hypervariable region 1 we investigated further whether initial viral de cline is correlated with changes in viral quasispecies distribution. In primary responders, ribavirin did not influence hepatitis C viremia decl ine which was of biphasic nature. Also in nonresponders HCV RNA levels decr eased after one week of treatment irrespectively of the mode of therapy (me an 10.0+/-2.3 to 5.5+/-1.1) (phase 1). In the following weeks, however, 2 t ypes of HCV dynamics could be observed (phase 2). In patients with combinat ion therapy, a further reduction of viremia level could be observed, wherea s viremia levels in patients with IFN alpha alone slightly increased (week 12: 3.0+/-0.5 MEq/mL [combination, n = 15] vs. 7.5+/-2.9 MEq/ mt [IFN alpha -mono, n = 12]). The individual response of these nonresponder patients sh owed, however, marked differences (range percentage decline after 4 weeks, 0-98%). Changes in the viral population (quasispecies distribution) as caus e of these differences could be excluded by SSCP-analysis of PCR products o f the HCV hypervariable region 1. Ribavirin in combination with IFN alpha exerts an additional anti-viral/imm unmodulatory effect which manifests itself in phase 2 of hepatitis C viremi a decline. The biphasic decline of hepatitis C viremia also observed in IFN alpha -nonresponders can not be explained by the selection of primary IFN alpha -resistant viral variants. The individual differences in the dynamic of hepatitis C viremia observed in the so called ,,nonresponders" imply tha t the term ,,nonresponder" should be redefined, considering our observation that a marked viral decline can occur in these patients.