Ribavirin-induced Hemolytic Anemia Research Articles

Chronic Hepatitis E Virus Manifesting as Elevated Transaminases in a Heart Transplant Patient

ABSTRACT Hepatitis E virus (HEV) is a common cause of viral hepatitis worldwide. Genotypes 1 and 2 cause acute hepatitis in endemic regions (Asia and Africa), whereas genotypes 3 and 4 (America and Europe) result in sporadic acute or chronic hepatitis, specifically in certain groups. HEV infections are rising because of increased transplantation rates and immunosuppression. We report a 75-year-old heart transplant patient with nonspecific symptoms, diagnosed with HEV chronic hepatitis. Despite ribavirin-induced hemolytic anemia, the patient achieved sustained virological response and normalization of liver enzymes.

Novel variant in glycophorin c gene protects against ribavirin-induced anemia during chronic hepatitis C treatment

BackgroundThe current use of ribavirin in difficult-to-cure chronic hepatitis C patients (HCV) and patients with severe respiratory infections is constrained by the issue of ribavirin-induced hemolytic anemia that affects 30% of treated patients, requiring dosage modification or discontinuation. Though some genetic variants have been identified predicting this adverse effect, known clinical and genetic factors do not entirely explain the risk of ribavirin-induced anemia. MethodsWe assessed the associations of previously identified variants in inosine triphosphatase (ITPA), solute carrier 28A2 (SLC28A2) and vitamin D receptor (VDR) genes with ribavirin-induced anemia defined as hemoglobin decline of ≥30 g/L on treatment, followed by a staged discovery (n = 114), replication (n = 74), and combined (n = 188) genome-wide association study to uncover potential new predictive variants. ResultsWe identified a novel association in the gene coding glycophorin C (rs6741425; OR:0.12, 95%CI:0.04–0.34, P = 2.94 × 10-6) that predicts protection against ribavirin-induced anemia. We also replicated the associations of ITPA and VDR genetic variants with the development of ribavirin-induced anemia (rs1127354; OR:0.13, 95%CI:0.04–0.41, P = 8.66 ×10-5; and rs1544410; OR:1.65, 95%CI:1.01–2.70, P = 0.0437). ConclusionsGYPC variation affecting erythrocyte membrane strength is important in predicting risk for developing ribavirin-induced anemia. ITPA and VDR genetic variants are also important predictors of this adverse reaction.

Predictive factors of anemia during sofosbuvir and ribavirin therapy for genotype 2 chronic hepatitis C patients.

Sofosbuvir (SOF) and ribavirin (RBV) combination therapy has improved the sustained virologic response (SVR) rate and shortened the treatment duration for patients with chronic hepatitis C virus (HCV) genotype 2 infection. Ribavirin-induced hemolytic anemia is one of the most troublesome side-effects of SOF/RBV therapy; however, factors associated with this condition have not been fully elucidated. We aimed to identify a safer way to complete treatment with SOF/RBV therapy by examining factors related to RBV-induced hemolytic anemia and identifying patients who did not develop anemia. Two hundred and one patients with genotype 2 chronic hepatitis C treated with SOF/RBV therapy were studied. Significant factors associated with the decline in hemoglobin (Hb) levels from the baseline were analyzed. The SVR rate was 96.5% (194 out of 201 patients) based on intent-to-treat analysis. In multivariate analysis, inosine triphosphatase (ITPA) gene variation (P < 0.0001) and estimated glomerular filtration rate (eGFR) (0.001) were significantly associated with a decrease in Hb levels less than 2g/dL. All patients were divided into four groups by ITPA and eGFR at baseline, and we identified patients with ITPA CA/AA and eGFR >75 as a group that did not develop anemia. The results presented here suggest that patients with ITPA CA/AA and eGFR >75 had no reduction in Hb levels during the treatment with SOF/RBV in HCV genotype 2-infected patients. Adding RBV to direct-acting antiviral therapy might not be problematic in certain patients, at least in terms of the occurrence of anemia.

Efficacy of L-carnitine on ribavirin-induced hemolytic anemia in patients with hepatitis C virus infection.

Background/AimsL-carnitine not only alleviates hyperammonemia and reduces muscle cramps in patients with liver cirrhosis, but also improves anemia in patients with chronic hepatitis and renal dysfunction. This study prospectively evaluated the preventative efficacy of L-carnitine supplementation against hemolytic anemia during antiviral treatment using ribavirin in patients with hepatitis C virus (HCV)-related chronic liver disease.MethodsA total of 41 patients with chronic hepatitis were consecutively enrolled in this study. Group A (n=22) received sofosbuvir plus ribavirin for 3 months, whereas group B (n=19) was treated with sofosbuvir, ribavirin, and L-carnitine. Hemoglobin concentration changes, the effects of antiviral treatment, and the health status of patients were analyzed using short form-8 questionnaires.ResultsA significantly smaller decrease in hemoglobin concentration was observed in group B compared to group A at every time point. Moreover, the prescribed dose intensity of ribavirin in group B was higher than that of group A, resulting in a higher ratio of sustained virological response (SVR) 24 in group B compared with group A. The physical function of patients in group B was also significantly improved compared to group A at the end of antiviral treatment.ConclusionsL-carnitine supplementation alleviates ribavirin-induced hemolytic anemia in patients with HCV and helps relieve the physical burden of treatment with ribavirin-containing regimens. These advantages significantly increase the likelihood of achieving SVR.

Pharmacogenomic Prediction of Ribavirin-Induced Hemolytic Anemia in Patients Treated for Hepatitis C Infection

Pharmacogenomic Prediction of Ribavirin-Induced Hemolytic Anemia in Patients Treated for Hepatitis C Infection

The relationship between ITPA rs1127354 polymorphisms and efficacy of antiviral treatment in Northeast Chinese CHC patients.

This prospective study investigated the relationship between 2 inosine triphosphatase (ITPA) polymorphisms (rs7270101 and rs1127354) and the efficacy of ribavirin-based antiviral therapy in hepatitis C virus (HCV)-infected Chinese patients.A total of 906 patients diagnosed with chronic hepatitis C receiving pegylated interferon (PEG-IFN) plus ribavirin combination therapy between January 2011 and January 2014 from 5 hepatitis centers in Northeast China were enrolled. The patients were divided into genotype 1 and non-genotype 1 groups according to the genotype of infected HCV. ITPA single nucleotide polymorphism (SNP) genotyping was performed for all patients. Ribavirin-induced hemolytic anemia and virological response (VR) were monitored during treatment and follow-up. Multivariate regression analysis was used to analyze the predictors for sustained virological response (SVR).IPTA rs7270101 variants were not detected. IPTA rs1127354 variants were detected and showed no difference between the genotype 1 and non-genotype 1 groups. IPTA rs1127354 genotype CC was related to a higher incidence of ribavirin-induced hemolytic anemia. For patients who received >80% of the planned ribavirin dose, rs1127354 variants and related ITPase were related to better SVR. Multivariate analysis showed that IPTA rs1127354 non-genotype CC, HCV genotype, a baseline HCV RNA level <4 × 105 IU/mL, IL-28B rs12979860 genotype CC, and low liver fibrosis were independent predictors for SVR during the combination therapy.IPTA rs1127354 variants and related ITPase were not only related with ribavirin-induced hemolytic anemia but also directly affected the SVR to PEG-IFN plus ribavirin combination therapy in Chinese HCV-infected patients.

High Prevalence of ITPA Alleles Associated with Ribavirin-Induced Hemolytic Anemia Among Mexican Population

Background. The prevalence of two functional polymorphisms (rs1127354 and rs7270101) of the inosine triphosphatase (ITPA) gene associated with ribavirin-induced hemolytic anemia (RIHA) during antiviral therapy for hepatitis C virus (HCV) infection varies by ethnicity. In Mexico, the distribution of these polymorphisms among Native Amerindians (NA) and admixed population (Mestizos) is unknown. This study aimed to determine the prevalence of the ITPA polymorphisms among healthy NA and Mestizos, as well as in HCV patients from West Mexico.Material and methods. In a cross-sectional study, 600 unrelated subjects (322 Mestizos, 100 NA, and 178 treatment-naïve, HCV-infected Mestizos patients) were enrolled. A medical history was registered. ITPA genotype was determined by Real-Time PCR. Fst-values and genetic relatedness between study and reference populations were assessed.Results. The frequency of the risk genotypes rs1127354CC and rs7270101AA was higher among NA (98-100%) than in Mestizos (87-92.9%), (p < 0.05). The NA presented the highest prevalence of the rs1127354CC genotype reported worldwide. The Fst-values revealed a genetic relatedness among Mexican NA, South Americans and African populations (p > 0.05). The frequency of the predicted risk for RIHA was higher among NA (98%) than in Mestizos (80.5%) and HCV-infected patients (81.5%) (p < 0 .01). The CC/AA alleles were associated with lower values of total bilirubin, aspartate/alanine aminotransferases, and aspartate-to-plate-let-ratio-index score among HCV-patients.Conclusion. A high prevalence of the ITPA polymorphisms associated with RIHA was found in Mexican NA. These polymorphisms could be a useful tool for evaluating potential adverse effects and the risk or benefit of antiviral therapy in Mexicans and other admixed populations.

Rapid CO breath test screening of drugs for protective effects on ribavirin-induced hemolysis in a rabbit model: a pilot study

Hemolytic anemia is a major side effect of ribavirin antiviral treatment for chronic hepatitis C. Ribavirin dose reduction may compromise the antiviral response and erythropoietin can take several weeks to alleviate anemia. The purpose of the present study was to screen potentially protective drugs against ribavirin-induced hemolytic anemia in a rabbit model, using our modified CO breath test for measuring erythrocyte (RBC) lifespan, the gold standard diagnostic index of hemolysis. Fifteen rabbits were divided randomly into five groups (N = 3/group): one vehicle control group, one ribavirin (only)-treated (RBV) group, and three groups initially treated with ribavirin only, followed by a combination of ribavirin with prednisone (RBV + Pred), polyene phosphatidyl choline (RBV + PPC), or reduced glutathione (RBV + GSH). RBC lifespan was calculated from accumulated CO measured in a closed rebreath apparatus, blood volume measured by the Evan’s blue dye (EBD) dilution test, and hemoglobin concentration data. The RBC lifespan was normal in the vehicle control group (44–60 d), but reduced significantly in all of the ribavirin-treated groups before the addition of screened drugs (17–35 d). RBC lifespan rebounded significantly with the addition of glutathione, but not with the addition of prednisone or polyene phosphatidyl choline. A similar overall drug effect pattern was seen in the hemoglobin concentration and reticulocyte count data. In conclusion, the results of this pilot study indicate that reduced glutathione can attenuate ribavirin-induced hemolytic anemia, and that the RBC lifespan measured with our modified rapid CO breath test is feasible and reliable for use in animal studies.

The birth and potential death of IL28B genotyping for hepatitis C therapy.

The birth and potential death of IL28B genotyping for hepatitis C therapy.

Analysis of human ITPase nucleobase specificity by site-directed mutagenesis

Inosine triphosphate (ITP) pyrophosphohydrolase, or ITPase, is an intracellular enzyme that is responsible for the hydrolysis of the acidic anhydride bond between the alpha and beta phosphates in ITP, and other noncanonical nucleoside triphosphates, producing the corresponding nucleoside monophosphate and pyrophosphate. This activity protects the cell by preventing noncanonical nucleoside triphosphates from accumulating in (deoxy) nucleoside triphosphate ((d)NTP) pools and/or being integrated into nucleic acids. This enzyme is encoded by the ITPA gene in mammals. It has been reported that Itpa homozygous-null knock-out mice die before weaning and have gross cardiac abnormalities. Additionally, certain variations in the human ITPA gene have been linked to adverse reactions to the immunosuppressive prodrugs azathioprine and 6-mercaptopurine and protection against ribavirin-induced hemolytic anemia. These drugs are bioactivated to form noncanonical nucleoside triphosphates. Human ITPase enzymes engineered to modulate nucleobase specificity may be valuable tools for studying the role of ITPase in heart development and drug metabolism or developing gain-of-function mutants or inhibitory molecules. Based on x-ray crystallography and amino acid sequence data, a panel of putative human ITPase nucleobase specificity mutants has been generated. We targeted eight highly conserved amino acid positions within the ITPase sequence that correspond to amino acids predicted to directly interact with the nucleobase or help organize the nucleobase binding pocket. The ability of the mutants to protect against exogenous and endogenous noncanonical purines was tested with two Escherichia coli complementation assays. Nucleobase specificity of the mutants was investigated with an in vitro biochemical assay using ITP, GTP and ATP as substrates. This methodology allowed us to identify gain-of-function mutants and categorize the eight amino acid positions according to their ability to protect against noncanonical purines as follows: Glu-22, Trp-151 and Arg-178, essential for protection; Phe-149, Asp-152, Lys-172 and Ser-176, intermediate protection; His-177, dispensable for protection against noncanonical purines.

Genetic variants at the ITPA locus protect against ribavirin-induced hemolytic anemia and dose reduction in an HCV G2/G3 cohort

Two functional genetic variants in the inosine triphosphatase (ITPA) gene have been shown to be strongly associated with protection from ribavirin (RBV)-induced hemolysis. We aimed at evaluating this finding in a chronic hepatitis C genotype 2/3 cohort with a predominance of genotype 3 patients where available data are scarce. A second objective was to determine whether a protective association translated into the need for RBV reduction and hence a possible impact on treatment response. Overall, 457 patients were recruited from two trials of genotype 2/3 patients treated with pegylated interferon α-2b and weight-based RBV. rs1127354 and rs7270101 were genotyped and a composite ITPAase deficiency variable was graded according to the two single nucleotide polymorphisms. The primary endpoints were hemoglobin (Hb) decline from baseline and Hb decline of more than 3 g/dl at week 4. Both single nucleotide polymorphisms and the composite ITPAase deficiency variable were strongly and independently associated with protection from a decline in Hb at week 4 in multivariate linear regression models (Prs1127354=7.0×10, Prs7270101=0.0036, PITPase deficiency variable =6.3×10). Patients with any degree of reduced ITPAase activity were less likely to have their RBV dose reduced (odds ratio 0.39, 95% confidence interval 0.16-0.96, P=0.040), although this did not translate into increased rapid viral response or sustained viral response (Prvr=0.93, Psvr=0.22). We have confirmed a strong association between functional ITPA variants and RBV-induced hemolysis and showed protection from RBV dose reduction, although this did not translate into increased rapid viral response or sustained viral response.

Prophylaxis for ribavirin‐related anemia using eicosapentaenoic acid in chronic hepatitis C patients

Ribavirin-related anemia is a serious side-effect of the pegylated interferon and ribavirin therapy used for hepatitis C, and may be cause for a reduction in ribavirin dose or even cessation of treatment. The aim of this study was to evaluate the prophylactic effects of oral eicosapentaenoic acid (EPA) supplementation on ribavirin-induced hemolytic anemia in pediatric and young adult patients. Twelve chronic hepatitis C patients ranging in age from 3 to 21 years (mean, 13.9 ± 5.1 years) who received pegylated interferon α-2b and ribavirin combination therapy were randomized to either the control group (n = 6) or EPA group (n = 6). Blood samples were collected before, and at 4, 8, and 16 weeks after treatment to measure clinical laboratory parameters. The reduction in hemoglobin levels of the EPA group was significantly ameliorated at 8 and 16 weeks when compared to the control group (P < 0.05). There was no significant difference in plasma ribavirin concentrations between the two groups during the treatment. However, one patient in the control group had a reduction in ribavirin dose. EPA supplementation prevented ribavirin-induced hemolytic anemia during combination therapy with pegylated interferon α-2b and ribavirin in pediatric and young adult patients.

Development and validation of a useful HPLC–UV method for quantification of total and phosphorylated-ribavirin in blood and erythrocytes of HCV+ patients

Ribavirin-induced hemolytic anemia is the main cause of discontinuation of the combination therapy with alpha-interferon-2b and ribavirin for the treatment of hepatitis C virus (HCV) infection. The determination of intracellular ribavirin levels in blood, including the levels of its phosphorylated metabolites, might be useful for predicting ribavirin-induced anemia, which could be caused by the accumulation of these molecules within the erythrocytes. In this work, we simplified and validated a previously developed assay method, to make it suitable for routine monitoring of cellular ribavirin. Whole blood diluted with a five-fold volume of ice-cold distilled underwent a process of acid phosphatase digestion to convert phosphorylated ribavirin metabolites to free ribavirin. The resulting mixture, spiked with an internal standard, was treated with a protein precipitation protocol in acetonitrile, followed by reverse-phase high-performance liquid chromatography analysis. The calibration curve for ribavirin levels in whole blood was linear at concentrations from 625 to 320,000 ng/mL (r(2)=0.998). Accuracy, intra-day and inter-day precision for ribavirin and phosphorylated-ribavirin quality controls were all below 9.0%. We tested this method by monitoring blood ribavirin concentrations in 13 HCV+ patients, receiving alpha interferon-plus ribavirin combination therapy.

Variants in the ITPA Gene Protect Against Ribavirin-Induced Hemolytic Anemia in HIV/HCV-Coinfected Patients With All HCV Genotypes

A recent genome-wide association study reported a strong association with a single-nucleotide polymorphism (SNP) in the inosine triphosphate (ITPA) gene and hemolytic anemia in patients infected with hepatitis C virus (HCV) receiving pegylated interferon and ribavirin. We investigate these polymorphisms in a cohort of human immunodeficiency virus (HIV)/HCV-coinfected patients. DNA was available for 161 patients with validated outcomes. We analyzed the association between the variants and week 4 hemoglobin reduction. Anemia over the course of therapy, ribavirin (RBV) dose reduction, serum RBV level, and rapid virological response (RVR) and sustained virological response (SVR) were also investigated. Using a candidate gene approach, ITPA variants rs1127354 and rs7270101 were tested using the ABI TaqMan kit. Multivariable models were used to identify predictors of anemia. A significant minority (33%) of patients were predicted to have reduced ITPase activity. The minor allele of each variant was associated with protection against week 4 anemia. In multivariable models only the genetic variants, creatinine, and zidovudine exposure remained significant. ITPase deficiency was not associated with RBV-dose reduction, RVR, or SVR. This study confirms that polymorphisms in the ITPA gene are associated with protection from RBV-induced anemia in HIV/HCV-coinfected patients but not improved clinical outcomes.

The Impact of Human Gene Polymorphisms on HCV Infection and Disease Outcome

In recent years, some genome-wide association studies have identified several single nucleotide polymorphisms (SNPs) associated with hepatitis C viral containment, treatment response, and disease progression. IL28B is a gene on chromosome 19, coding for interferon-λ3, and two polymorphisms upstream of this the gene have been strongly associated with clinical outcomes after treatment for the hepatitis C virus (HCV). The IL28B polymorphisms have additionally been associated with spontaneous clearance. The mechanism has yet to be clearly defined, but appears to involve differential responsiveness to interferon signaling between the favorable and unfavorable genotypes. ITPA is a gene on chromosome 20, coding for inosine triphosphatase, and polymorphisms on this gene have been associated with ribavirin-induced hemolytic anemia. Functional variants of ITPA have been identified that have decreased enzymatic activity, which appear to protect against anemia. Finally, PNPLA3 polymorphisms were initially described as predictors of nonalcoholic fatty liver disease, but have recently been associated with disease progression in HCV.

Taribavirin in the treatment of hepatitis C

Introduction:Treatment of chronic hepatitis C virus (HCV) is limited by substantial side effects including ribavirin-induced hemolytic anemia. Taribavirin, a ribavirin prodrug, was designed to concentrate within the liver to target HCV-infected hepatocytes while minimizing distribution within red blood cells (RBCs) and the subsequent development of hemolytic anemia.Areas covered:The objective of the review is to evaluate the efficacy and safety of taribavirin as compared with ribavirin in the treatment of chronic HCV infections. A PubMed search was performed using the following key words: viramidine, taribavirin and ribavirin analog. Additional sources included press releases on preliminary results of clinical trials of taribavirin and abstracts presented at international meetings. The literature suggests that weight-based dosing of taribavirin at 25 mg/kg demonstrates lower rates of hemolytic anemia with comparable rates of sustained virologic response (SVR) and is the optimum dose for further studies comparing the efficacy of taribavirin with weight-based dosing of ribavirin.Expert opinion:Failure to eradicate HCV may be associated with extrahepatic viral replication. The dosing strategy of taribavirin favors concentration within the liver to reduce treatment-limiting rates of anemia but may be insufficient to prevent virologic relapse.

The Effects of IL-28B and ITPA Polymorphisms on Treatment of Hepatitis C Virus Genotype 6

To the editor: We read with interest a review article by Clark et al. (1). Two single-nucleotide polymorphisms (SNPs; rs12979860 and rs8099917) around the interleukin (IL)-28B gene locus were found by genome-wide association studies (GWAS) to be independent predictors of treatment response for hepatitis C virus (HCV) genotype 1. Other SNPs of interest identified by GWAS in HCV are the inosine triphosphatase (ITPA) gene polymorphisms (one of which is rs1127354). It is associated with protection from ribavirin-induced hemolytic anemia in genotype 1 patients (2).

Virologic response rates of weight-based taribavirin versus ribavirin in treatment-naive patients with genotype 1 chronic hepatitis C

Ribavirin-induced hemolytic anemia can prompt dose reductions and lower sustained virologic response (SVR) rates in the treatment of patients with chronic hepatitis C. The study aimed to determine if weight-based dosing of taribavirin (TBV), an oral prodrug of ribavirin (RBV), demonstrated efficacy comparable to RBV while maintaining its previously demonstrated anemia advantage with fixed dose administration. A U.S. phase 2b randomized, open-label, active-controlled, parallel-group study was conducted in 278 treatment-naive patients infected with genotype 1 who were stratified by body weight and baseline viral load. Patients were randomized 1:1:1:1 to receive TBV (20, 25, or 30 mg/kg/day) or RBV (800-1400 mg/day) with pegylated interferon alfa-2b for 48 weeks. The SVR rates in this difficult-to-cure patient demographics (mean age, 49 years; 61% male; 30% African American or Latino; high viral load; advanced fibrosis; and mean weight, 82 kg) were 28.4%, 24.3%, 20.6%, and 21.4% in the 20, 25, and 30 mg/kg TBV groups and the RBV group, respectively. There were no statistical differences in the efficacy analyses. Anemia rates were significantly lower (P < 0.05) in the 20 and 25 mg/kg/day TBV treatment groups (13.4% and 15.7%, respectively) compared to RBV (32.9%). The most common adverse events in all groups were fatigue, diarrhea, and insomnia. Diarrhea, reported in 38% of TBV patients versus 21% of RBV patients, was generally mild and not dose-limiting. All TBV doses demonstrated efficacy and tolerability comparable to that of RBV; however, the 25 mg/kg dose demonstrated the optimal balance of safety and efficacy. Anemia rates were significantly lower for TBV given at 20-25 mg/kg than RBV. These data suggest weight-based dosing with TBV provides a safe and effective treatment alternative to RBV for chronic hepatitis C. American Association for the Study of Liver Diseases.

Variants in the ITPA Gene Protect Against Ribavirin-Induced Hemolytic Anemia and Decrease the Need for Ribavirin Dose Reduction

In a genome-wide association study of patients being treated for chronic hepatitis C, 2 functional variants in ITPA that cause inosine triphosphatase (ITPase) deficiency were shown to protect against ribavirin (RBV)-induced hemolytic anemia during early stages of treatment. We aimed to replicate this finding in an independent cohort from the Study of Viral Resistance to Antiviral Therapy of Chronic Hepatitis C and to investigate the effects of these variants beyond week 4. Genetic material was available from 318 patients. The ITPA variants, rs1127354 (exon 2, P32T) and rs7270101 (intron 2, splice altering), were genotyped and tested for association with hemoglobin (Hb) reduction at week 4. An ITPase deficiency variable was defined that combined both ITPA variants according to documented effect on ITPase activity. We investigated the impact of ITPA variants on Hb levels over the course of therapy and on the need for RBV dose reduction. The final analysis included 304 patients with genotype 1 hepatitis C virus (167 white patients and 137 black patients). The polymorphisms rs1127354 and rs7270101 were associated with Hb reduction at week 4 (P = 3.1 × 10(-13) and 1.3 × 10(-3), respectively). The minor alleles of each variant protected against Hb reduction. Combining the variants into the ITPase deficiency variable strengthened the association (P = 2.4 × 10(-18)). The ITPase deficiency variable was associated with lower rates of anemia over the entire treatment period (48 weeks), as well as a lower rate of anemia-related RBV dose reduction (hazard ratio, 0.52; P = .0037). No association with sustained virological response was observed. Two polymorphisms that cause ITPase deficiency are strongly associated with protection from RBV-induced hemolytic anemia and decrease the need for RBV dose reduction.

Variants in the ITPA Gene Protect Against Ribavirin-Induced Hemolytic Anemia and Decrease the Need for Ribavirin Dose Reduction

Variants in the ITPA Gene Protect Against Ribavirin-Induced Hemolytic Anemia and Decrease the Need for Ribavirin Dose Reduction