Improved Virologic Response in Chronic Hepatitis C Genotype 4 Treated With Nitazoxanide, Peginterferon, and Ribavirin
Gastroenterology March 2009
Jean-Francois Rossignol, Asem Elfert, Yehia El-Gohary, Emmet B. Keeffe
Background & Aims
Sustained virologic response (SVR) rates of 50%-60% have been achieved in patients with chronic hepatitis C genotype 4 treated with peginterferon plus ribavirin. The safety and efficacy of nitazoxanide plus peginterferon alfa-2a, with or without ribavirin, were evaluated in a randomized controlled trial at 2 centers in Egypt.
Previously untreated patients with chronic hepatitis C and genotype 4 infection were assigned randomly to groups that were given standard of care (peginterferon alfa-2a and ribavirin for 48 weeks, n = 40), nitazoxanide monotherapy for 12 weeks followed by nitazoxanide plus peginterferon alfa-2a for 36 weeks (n = 28), or nitazoxanide monotherapy for 12 weeks followed by nitazoxanide plus peginterferon alfa-2a and ribavirin for 36 weeks (n = 28). Therapeutics included nitazoxanide (500 mg) twice daily, peginterferon alfa-2a (180 Ęg) once weekly, and weight-based ribavirin (1000-1200 mg/day).
The percentages of rapid virologic response (RVR), defined as undetectable HCV RNA at week 4 of combination therapy, and SVR were significantly higher in patients given the triple therapy compared with the standard of care (64% vs 38%, P = .048; and 79% vs 50%, P = .023; respectively). Patients given nitazoxanide plus peginterferon alfa-2a had intermediate rates of RVR (54%) and SVR (61%). Adverse events were similar across treatment groups except for higher rates of anemia in the groups receiving ribavirin.
The combination of nitazoxanide, peginterferon alfa-2a, and ribavirin increased the percentages of patients with RVR and SVR, compared with patients given peginterferon plus ribavirin, without an increase in adverse events.
Chronic hepatitis C virus (HCV) infects approximately 170 million individuals worldwide and is a major cause of morbidity and mortality.1 These factors, as well as suboptimal response rates to standard therapy with 48 weeks of peginterferon and ribavirin, have led to an extensive search for novel therapies.
Nitazoxanide is the first member of the thiazolide class of anti-infective compounds.2 It is an oral agent that was developed originally as an antiparasitic drug and has no major side effects. Nitazoxanide is licensed in the United States as Alinia (Romark Laboratories, L.C., Tampa, FL) for the treatment of Cryptosporidium parvum and Giardia lamblia. During the course of early drug development, it was noted that some patients with cryptosporidiosis and acquired immune deficiency syndrome who were co-infected with HCV or hepatitis B virus (HBV) had a reduction in serum alanine aminotransferase (ALT) levels with long-term nitazoxanide therapy. This observation led to studies of the antiviral activity of nitazoxanide and its active metabolite, tizoxanide, in HCV genotype 1a and 1b replicons and a genotype 2 infectious clone, which showed potent inhibition of HCV replication by both compounds at submicromolar concentrations.3 In addition, pretreatment of HCV replicon-containing cells with nitazoxanide was shown to enhance the antiviral effect of subsequent treatment with nitazoxanide plus interferon.3 More recently, studies of the mechanism of action of nitazoxanide against HCV have shown that it induces double-stranded RNA-activated protein kinase (PKR) phosphorylation, which results in an increased intracellular concentration of phosphorylated eukaryotic initiation factor 2α, a key mediator of host cell defenses against viral infection.4
A phase II, randomized, double-blind, placebo-controlled study of nitazoxanide treatment for 24 weeks in 50 patients with chronic hepatitis C genotype 4 was conducted to evaluate safety with prolonged administration and to determine the antiviral efficacy of nitazoxanide monotherapy.5 In this study, 7 of 23 patients (30.4%) treated with nitazoxanide achieved undetectable serum HCV RNA compared with 0 of 24 in the placebo group at the end of treatment, and 4 patients (17.4% of 23 treated) had a sustained virologic response (SVR).5 All responders had baseline serum HCV RNA levels of 400,000 IU/mL or less. This monotherapy study was followed by an initial pilot experience showing increased virologic response rates with nitazoxanide plus peginterferon and greater efficacy if nitazoxanide was administered initially as monotherapy during a lead-in phase before beginning combination therapy with peginterferon.
The earlier-described clinical and laboratory observations prompted the current study, whose objective was to assess the safety and antiviral efficacy of nitazoxanide in combination with peginterferon alfa-2a, with or without ribavirin, for the treatment of patients with chronic hepatitis C infected with genotype 4.
In this study, triple therapy with peginterferon, ribavirin, and nitazoxanide for 36 weeks after a 12-week lead-in with nitazoxanide monotherapy achieved an SVR rate of 79% in treatment-naive patients with chronic hepatitis C infected with genotype 4, which was superior to the SVR rate achieved with the standard of care using peginterferon plus ribavirin for 48 weeks (50%; P = .023). The peginterferon plus nitazoxanide dual-treatment regimen produced an SVR rate of 61%, which was higher than the SVR achieved with the standard of care (50%) and represented a difference of 11% (95% confidence interval, |15% to +34%), although this difference was not statistically different. There were no added side effects associated with the use of nitazoxanide.
The higher SVR rates in the nitazoxanide groups were associated with higher RVR rates and mean reductions in serum HCV RNA levels after 4 weeks of combination therapy (Table 2). The proportion of patients achieving a RVR with triple therapy with peginterferon, ribavirin, and nitazoxanide was significantly higher than for the standard of care with peginterferon plus ribavirin arm (64% vs 38%; P = .048). The mean reduction in serum HCV RNA levels from baseline to the RVR time point in the triple therapy group receiving peginterferon, ribavirin, and nitazoxanide also was significantly higher than the peginterferon plus ribavirin standard of care group (|4.5 log10 IU/mL vs |2.86 log10 IU/mL; P = .013, respectively). Finally, it should be noted that the use of nitazoxanide in the dual- and triple-treatment arms was associated with reduced relapse rates (3/20 patients and 1/23 patients, respectively) compared with the standard of care arm (10/30 patients) (Table 2).
The number of patients enrolled in this phase II clinical trial was relatively small, leaving the potential for differences in patient characteristics between groups that may have contributed to the observed results. In addition, the fact that patients and physicians were not blinded to treatment group assignments could have influenced adherence to the protocol.. Nevertheless, exploratory analyses did not reveal any differences in patient characteristics or adherence to the protocol that could explain the observed differences in response rates between groups.
An important limitation of this study is the fact that it was conducted in patients infected with HCV genotype 4. The early clinical development of nitazoxanide in chronic hepatitis C was conducted in Egypt after the conclusion of a large clinical development program evaluating the role of nitazoxanide for the treatment of multiple causes of infectious diarrhea and gastroenteritis. Chronic hepatitis C is particularly common in Egypt, with an estimated prevalence rate of 15%, and approximately 90% of patients are infected with HCV genotype 4.9 The SVR rate for treatment of chronic hepatitis C genotype 4 using the standard of care ranges from less than 50% to more than 60%.10 After controlling for factors affecting virologic response, SVR rates for genotype 4 generally are reported to be similar to or slightly higher than those of genotype 1, but lower than genotypes 2 and 3.11 Although HCV genotype 4 is the predominant genotype in the Middle East and is becoming more important in other parts of the world as a result of immigration, only approximately 3% of the 170 million people chronically infected with HCV are infected with genotype 4. Worldwide, the dominant genotype is HCV genotype 1, accounting for approximately 70% of all infections.1 At present, there are no genotype 4 replicon models to assess inhibition of HCV by nitazoxanide in vitro. However, laboratory studies have shown that nitazoxanide is a potent inhibitor of HCV replication in genotype 1a- and 1b-derived replicons and in a genotype 2 infectious clone,3 suggesting that antiviral efficacy likely also will be shown in patients infected with genotype 1 treated with nitazoxanide combination therapy. However, the results of this study in patients with genotype 4 need to be confirmed in clinical trials conducted in patients infected with the HCV genotype 1, which currently are ongoing in the United States.
The rationale for a nitazoxanide lead-in phase before combined therapy with peginterferon, with or without ribavirin, was based on an initial pilot experience that showed greater antiviral efficacy if nitazoxanide was administered before peginterferon rather than simultaneously. This clinical experience was supported by laboratory studies in the HCV replicon model showing that pretreatment with nitazoxanide enhanced the effect of subsequent treatment with nitazoxanide plus interferon.3 During the 12-week lead-in phase in the current study, nitazoxanide monotherapy produced a modest -0.27 log10 IU decrease in serum HCV RNA level, with 2 patients experiencing a decrease from baseline of greater than 1 log10 IU/mL, including 1 patient who cleared serum HCV RNA. This was not an unexpected finding because an earlier phase II study showed a modest antiviral effect of nitazoxanide monotherapy in patients with chronic hepatitis C, with 4 of 23 patients (17.4%) experiencing a SVR.5
The required duration of a nitazoxanide lead-in phase is unknown, and 12 weeks was selected as an initial conservative estimate to optimize the potential benefit of nitazoxanide pretreatment. A subsequent study has shown that a 4-week lead-in phase may be satisfactory, and this study also provides further confirmation of the antiviral efficacy of nitazoxanide combined with peginterferon. In this open-label study,12 44 treatment-naive patients with chronic hepatitis C were treated with 4 weeks of nitazoxanide 500 mg twice daily followed by combination dual therapy with peginterferon alfa-2a 180 Ęg weekly plus nitazoxanide 500 mg twice daily for an additional 36 weeks. Interestingly, the SVR rate with dual therapy (80%) was similar to the SVR rate with triple therapy (79%) seen in the current study using a 12-week lead-in phase. This shorter lead-in period appears to be adequate, and future studies are underway using the 4-week lead-in before combination therapy. Further study of the nitazoxanide plus peginterferon regimen for the treatment of chronic hepatitis C is warranted, especially in patients unable to tolerate ribavirin.
In a preliminary experience with interferon nonresponders, a small number of patients with chronic hepatitis C genotype 4 who had failed prior interferon-based therapy were re-treated using triple therapy with nitazoxanide, peginterferon, and ribavirin and achieved an SVR rate of 25% (3/12 patients) compared with 8% (1/12 patients) retreated with the standard of care using peginterferon alfa-2a plus ribavirin.13 Further studies of nitazoxanide plus peginterferon and ribavirin in nonresponder patients with chronic hepatitis C infected with genotype 1 are underway in the United States.
The mechanism of action of nitazoxanide in protozoa and anaerobic bacteria has been shown to result from direct inhibition of pyruvate ferredoxin oxidoreductase enzyme-dependent electron transfer reaction, which is essential to anaerobic energy metabolism.14 However, the antiviral mechanism of action of nitazoxanide appears to be different. Recent studies suggest that nitazoxanide and other thiazolides selectively induce double-stranded RNA-activated protein kinase PKR phosphorylation, which leads to increased cell concentration of phosphorylated eukaryotic initiation factor 2α, a naturally occurring antiviral intracellular protein.4 This mechanism of action is triggered only when a cell is infected with HCV whereas nitazoxanide has no effect in uninfected cells, which provides a potential explanation for its very low rate of toxicity. Finally, nitazoxanide does not appear to induce antiviral resistance based on an attempt to produce resistance to nitazoxanide and tizoxanide in HCV replicon-containing cell lines.15 With serial exposure to nitazoxanide or tizoxanide, direct HCV viral resistance did not emerge, suggesting that the genetic barrier to the development of resistance to nitazoxanide is high.
This study reports the safety and efficacy of nitazoxanide in combination with peginterferon, with or without ribavirin, for the treatment of chronic hepatitis C. The results of this study have been confirmed in a subsequent open-label study of an additional 44 patients with chronic hepatitis C infected predominantly with genotype 4 but also including 4 patients with genotypes 1 and 2.12 These results show that nitazoxanide, a novel protein kinase inducer, has the potential not only to increase the SVR rate but potentially to shorten the duration of therapy. Further studies are underway to test these hypotheses in both naive and nonresponder patient populations infected with genotype 1, as well as with a controlled-release nitazoxanide tablet that has the potential to enhance the efficacy of the standard nitazoxanide formulation shown in this study.