RIBAVIRIN

Ribavirin, is a nucleoside analogue with antiviral activity. The chemical name of ribavirin is 1-β-D-­ribofuranosyl-1 H -1,2,4-triazole-3-carboxamide and has the following structural formula: The molecular formula of ribavirin is C 8 H 12 N 4 O 5 and the molecular weight is 244.2. Ribavirin USP is a white crystalline powder. It is freely soluble in water and slightly soluble in anhydrous alcohol. Ribavirin USP is available as a light pink colored, capsule shaped, film-coated tablet for oral administration. Each tablet contains 200 mg of ribavirin USP and the following inactive ingredients: microcrystalline cellulose, pregelatinised starch (maize), sodium starch glycolate, povidone (Kollidon 30), colloidal silicon dioxide, magnesium stearate, ethyl cellulose, triacetin, hypromellose, iron oxide red, titanium dioxide, and yellow iron oxide. Chemical Structure

Ribavirin tablets in combination with PEGASYS ® (peginterferon alfa-2a) are indicated for the treatment of patients 5 years of age and older with chronic hepatitis C (CHC) virus infection who have compensated liver disease and have not been previously treated with interferon alpha. The following points should be considered when initiating ribavirin tablets combination therapy with PEGASYS ® : This indication is based on clinical trials of combination therapy in patients with CHC and compensated liver disease, some of whom had histological evidence of cirrhosis (Child-Pugh class A), and in adult patients with clinically stable HIV disease and CD4 count greater than 100 cells/mm 3 . This indication is based on achieving undetectable HCV RNA after treatment for 24 or 48 weeks, based on HCV genotype, and maintaining a Sustained Virologic Response (SVR) 24 weeks after the last dose. Safety and efficacy data are not available for treatment longer than 48 weeks. The safety and efficacy of ribavirin tablets and PEGASYS ® therapy have not been established in liver or other organ transplant recipients, patients with decompensated liver disease, or previous non-responders to interferon therapy. The safety and efficacy of ribavirin tablets therapy for the treatment of adenovirus, RSV, parainfluenza or influenza infections have not been established. Ribavirin tablets should not be used for these indications. Ribavirin for inhalation has a separate package insert, which should be consulted if ribavirin inhalation therapy is being considered. Ribavirin tablets are a nucleoside analogue indicated for the treatment of chronic hepatitis C (CHC) virus infection in combination with PEGASYS ® in patients 5 years of age and older with compensated liver disease not previously treated with interferon alpha, and in adult CHC patients coinfected with HIV (1)

Ribavirin tablets should be taken with food. Ribavirin tablets should be given in combination with PEGASYS ® ; it is important to note that ribavirin tablets should never be given as monotherapy. See PEGASYS ® Package Insert for all instructions regarding PEGASYS ® dosing and administration. CHC: Ribavirin tablets are administered according to body weight and genotype (2.1) CHC with HIV coinfection: 800 mg by mouth daily for a total of 48 weeks, regardless of genotype (2.2) Dose reduction or discontinuation is recommended in patients experiencing certain adverse reactions or renal impairment (2.3 , 2.4) 2.1 Chronic Hepatitis C Monoinfection Adult Patients The recommended dose of ribavirin tablets is provided in Table 1 . The recommended duration of treatment for patients previously untreated with ribavirin and interferon is 24 to 48 weeks. The daily dose of ribavirin tablets is 800 mg to 1200 mg administered orally in two divided doses. The dose should be individualized to the patient depending on baseline disease characteristics (e.g., genotype), response to therapy, and tolerability of the regimen (see Table 1 ). Table 1 PEGASYS ® and Ribavirin Tablets Dosing Recommendations Genotypes 2 and 3 showed no increased response to treatment beyond 24 weeks (see Table 10 ). Data on genotypes 5 and 6 are insufficient for dosing recommendations. * See PEGASYS ® Package Insert for further details on PEGASYS ® dosing and administration, including dose modification in patients with renal impairment. Hepatitis C Virus (HCV) Genotype PEGASYS ® Dose* (once weekly) Ribavirin Tablets Dose (daily) Duration Genotypes 1, 4 180 mcg <75 kg = 1000 mg ≥75 kg = 1200 mg 48 weeks 48 weeks Genotypes 2, 3 180 mcg 800 mg 24 weeks Pediatric Patients PEGASYS ® is administered as 180 mcg/1.73m 2 x BSA once weekly subcutaneously, to a maximum dose of 180 mcg, and should be given in combination with ribavirin. The recommended treatment duration for patients with genotype 2 or 3 is 24 weeks and for other genotypes is 48 weeks. Ribavirin tablets should be given in combination with PEGASYS ® . Ribavirin tablets are available only as a 200 mg tablet and therefore the healthcare provider should determine if this sized tablet can be swallowed by the pediatric patient. The recommended doses for ribavirin tablets are provided in Table 2 . Patients who initiate treatment prior to their 18 th birthday should maintain pediatric dosing through the completion of therapy. Table 2 Ribavirin Tablets Dosing Recommendations for Pediatric Patients *approximately 15 mg/kg/day Body Weight in kilograms (kg) Ribavirin Tablets Daily Dose* Ribavirin Tablets Number of Tablets 23 to 33 400 mg/day 1 x 200 mg tablet A.M. 1 x 200 mg tablet P.M. 34 to 46 600 mg/day 1 x 200 mg tablet A.M. 2 x 200 mg tablets P.M. 47 to 59 800 mg/day 2 x 200 mg tablets A.M. 2 x 200 mg tablets P.M. 60 to 74 1000 mg/day 2 x 200 mg tablets A.M. 3 x 200 mg tablets P.M. ≥75 1200 mg/day 3 x 200 mg tablets A.M. 3 x 200 mg tablets P.M. 2.2 Chronic Hepatitis C with HIV Coinfection Adult Patients The recommended dose for treatment of chronic hepatitis C in patients coinfected with HIV is PEGASYS ® 180 mcg subcutaneous once weekly and ribavirin tablets 800 mg by mouth daily for a total duration of 48 weeks, regardless of HCV genotype. 2.3 Dose Modifications Adult and Pediatric Patients If severe adverse reactions or laboratory abnormalities develop during combination ribavirin tablets/PEGASYS ® therapy, the dose should be modified or discontinued, if appropriate, until the adverse reactions abate or decrease in severity. If intolerance persists after dose adjustment, ribavirin tablets/PEGASYS ® therapy should be discontinued. Table 3 provides guidelines for dose modifications and discontinuation based on the patient’s hemoglobin concentration and cardiac status. Ribavirin tablets should be administered with caution to patients with pre-existing cardiac disease. Patients should be assessed before commencement of therapy and should be appropriately monitored during therapy. If there is any deterioration of cardiovascular status, therapy should be stopped [see Warnings and Precautions (5.2) ] . Table 3 Ribavirin Tablets Dose Modification Guidelines in Adults and Pediatrics Body weight in kilograms (kg) Laboratory Values Hemoglobin <10 g/dL in patients with no cardiac disease, or Decrease in hemoglobin of ≥2 g/dL during any 4 week period in patients with history of stable cardiac disease Hemoglobin <8.5 g/dL in patients with no cardiac disease, or Hemoglobin <12 g/dL despite 4 weeks at reduced dose in patients with history of stable cardiac disease Adult Patients older than 18 years of age Any weight 1 x 200 mg tablet A.M. 2 x 200 mg tablets P.M. Discontinue ribavirin tablets Pediatric Patients 5 to 18 years of age 23 to 33 kg 1 x 200 mg tablet A.M. Discontinue ribavirin tablets 34 to 46 kg 1 x 200 mg tablet A.M. 1 x 200 mg tablet P.M. 47 to 59 kg 1 x 200 mg tablet A.M. 1 x 200 mg tablet P.M. 60 to 74 kg 1 x 200 mg tablet A.M. 2 x 200 mg tablets P.M. ≥75 kg 1 x 200 mg tablet A.M. 2 x 200 mg tablets P.M. The guidelines for ribavirin tablets dose modifications outlined in this table also apply to laboratory abnormalities or adverse reactions other than decreases in hemoglobin values. Adult Patients Once ribavirin tablets have been withheld due to either a laboratory abnormality or clinical adverse reaction, an attempt may be made to restart ribavirin tablets at 600 mg daily and further increase the dose to 800 mg daily. However, it is not recommended that ribavirin tablets be increased to the original assigned dose (1000 mg to 1200 mg). Pediatric Patients Upon resolution of a laboratory abnormality or clinical adverse reaction, an increase in ribavirin tablets dose to the original dose may be attempted depending upon the physician’s judgment. If ribavirin tablets have been withheld due to a laboratory abnormality or clinical adverse reaction, an attempt may be made to restart ribavirin tablets at one-half the full dose. 2.4 Renal Impairment The total daily dose of ribavirin tablets should be reduced for patients with creatinine clearance less than or equal to 50 mL/min; and the weekly dose of PEGASYS ® should be reduced for creatinine clearance less than 30 mL/min as follows in Table 4 [see Use in Specific Populations (8.7) , Pharmacokinetics (12.3) , and PEGASYS ® Package Insert] . Table 4 Dosage Modification for Renal Impairment Creatinine Clearance PEGASYS ® Dose (once weekly) Ribavirin Tablets Dose (daily) 30 to 50 mL/min 180 mcg Alternating doses, 200 mg and 400 mg every other day Less than 30 mL/min 135 mcg 200 mg daily Hemodialysis 135 mcg 200 mg daily The dose of ribavirin tablets should not be further modified in patients with renal impairment. If severe adverse reactions or laboratory abnormalities develop, ribavirin tablets should be discontinued, if appropriate, until the adverse reactions abate or decrease in severity. If intolerance persists after restarting ribavirin tablets, ribavirin tablets/PEGASYS ® therapy should be discontinued. No data are available for pediatric subjects with renal impairment. 2.5 Discontinuation of Dosing Discontinuation of PEGASYS ® /ribavirin tablets therapy should be considered if the patient has failed to demonstrate at least a 2 log 10 reduction from baseline in HCV RNA by 12 weeks of therapy, or undetectable HCV RNA levels after 24 weeks of therapy. PEGASYS ® /Ribavirin tablets therapy should be discontinued in patients who develop hepatic decompensation during treatment [see Warnings and Precautions (5.3) ] .

Ribavirin tablets are contraindicated in: Women who are pregnant. Ribavirin tablets may cause fetal harm when administered to a pregnant woman. Ribavirin tablets are contraindicated in women who are or may become pregnant. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to the fetus [see Warnings and Precautions (5.1) , Use in Specific Populations (8.1) , and Patient Counseling Information (17) ] . Men whose female partners are pregnant. Patients with hemoglobinopathies (e.g., thalassemia major or sickle-cell anemia). In combination with didanosine. Reports of fatal hepatic failure, as well as peripheral neuropathy, pancreatitis, and symptomatic hyperlactatemia/lactic acidosis have been reported in clinical trials [see Drug Interactions (7.1) ] . Ribavirin tablets and PEGASYS ® combination therapy are contraindicated in patients with: Autoimmune hepatitis. Hepatic decompensation (Child-Pugh score greater than 6; class B and C) in cirrhotic CHC monoinfected patients before treatment [see Warnings and Precautions (5.3) ] . Hepatic decompensation (Child-Pugh score greater than or equal to 6) in cirrhotic CHC patients coinfected with HIV before treatment [see Warnings and Precautions (5.3) ] . Pregnant women and men whose female partners are pregnant (4 , 5.1 , 8.1 ) Hemoglobinopathies (4) Coadministration with didanosine (4 , 7.1) Ribavirin tablets in combination with PEGASYS ® are contraindicated in patients with: Autoimmune hepatitis (4) Hepatic decompensation in cirrhotic patients (4 , 5.3)

PEGASYS ® in combination with ribavirin causes a broad variety of serious adverse reactions [see Boxed Warning and Warnings and Precautions (5) ] . The most common serious or life-threatening adverse reactions induced or aggravated by ribavirin/PEGASYS ® include depression, suicide, relapse of drug abuse/overdose, and bacterial infections each occurring at a frequency of less than 1%. Hepatic decompensation occurred in 2% (10/574) CHC/HIV patients [see Warnings and Precautions (5.3) ] . The most common adverse reactions (frequency greater than 40%) in adults receiving combination therapy are fatigue/asthenia, pyrexia, myalgia, and headache. (6.1) The most common adverse reactions in pediatric subjects were similar to those seen in adults. (6.1) To report SUSPECTED ADVERSE REACTIONS, contact Aurobindo Pharma USA, Inc. at 1-866-850-2876 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Studies Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice. Adult Patients In the pivotal registration trials NV15801 and NV15942, 886 patients received ribavirin for 48 weeks at doses of 1000/1200 mg based on body weight. In these trials, one or more serious adverse reactions occurred in 10% of CHC monoinfected subjects and in 19% of CHC/HIV subjects receiving PEGASYS ® alone or in combination with ribavirin. The most common serious adverse event (3% in CHC and 5% in CHC/HIV) was bacterial infection (e.g., sepsis, osteomyelitis, endocarditis, pyelonephritis, pneumonia). Other serious adverse reactions occurred at a frequency of less than 1% and included: suicide, suicidal ideation, psychosis, aggression, anxiety, drug abuse and drug overdose, angina, hepatic dysfunction, fatty liver, cholangitis, arrhythmia, diabetes mellitus, autoimmune phenomena (e.g., hyperthyroidism, hypothyroidism, sarcoidosis, systemic lupus erythematosus, rheumatoid arthritis), peripheral neuropathy, aplastic anemia, peptic ulcer, gastrointestinal bleeding, pancreatitis, colitis, corneal ulcer, pulmonary embolism, coma, myositis, cerebral hemorrhage, thrombotic thrombocytopenic purpura, psychotic disorder, and hallucination. The percentage of patients in clinical trials who experienced one or more adverse events was 98%. The most commonly reported adverse reactions were psychiatric reactions, including depression, insomnia, irritability, anxiety, and flu-like symptoms such as fatigue, pyrexia, myalgia, headache and rigors. Other common reactions were anorexia, nausea and vomiting, diarrhea, arthralgias, injection site reactions, alopecia, and pruritus. Table 5 shows rates of adverse events occurring in greater than or equal to 5% of subjects receiving pegylated interferon and ribavirin combination therapy in the CHC Clinical Trial, NV15801. Ten percent of CHC monoinfected patients receiving 48 weeks of therapy with PEGASYS ® in combination with ribavirin discontinued therapy; 16% of CHC/HIV coinfected patients discontinued therapy. The most common reasons for discontinuation of therapy were psychiatric, flu-like syndrome (e.g., lethargy, fatigue, headache), dermatologic and gastrointestinal disorders, and laboratory abnormalities (thrombocytopenia, neutropenia, and anemia). Overall 39% of patients with CHC or CHC/HIV required modification of PEGASYS ® and/or ribavirin therapy. The most common reason for dose modification of PEGASYS ® in CHC and CHC/HIV patients was for laboratory abnormalities; neutropenia (20% and 27%, respectively) and thrombocytopenia (4% and 6%, respectively). The most common reason for dose modification of ribavirin in CHC and CHC/HIV patients was anemia (22% and 16%, respectively). PEGASYS ® dose was reduced in 12% of patients receiving 1000 mg to 1200 mg ribavirin for 48 weeks and in 7% of patients receiving 800 mg ribavirin for 24 weeks. Ribavirin dose was reduced in 21% of patients receiving 1000 mg to 1200 mg ribavirin for 48 weeks and in 12% of patients receiving 800 mg ribavirin for 24 weeks. Chronic hepatitis C monoinfected patients treated for 24 weeks with PEGASYS ® and 800 mg ribavirin were observed to have lower incidence of serious adverse events (3% vs. 10%), hemoglobin less than 10 g/dL (3% vs. 15%), dose modification of PEGASYS ® (30% vs. 36%) and ribavirin (19% vs. 38%), and of withdrawal from treatment (5% vs. 15%) compared to patients treated for 48 weeks with PEGASYS ® and 1000 mg or 1200 mg ribavirin. On the other hand, the overall incidence of adverse events appeared to be similar in the two treatment groups. Table 5 Adverse Reactions Occurring in Greater Than or Equal to 5% of Patients in Chronic Hepatitis C Clinical Trials (Study NV15801) * Severe hematologic abnormalities (lymphocyte less than 500 cells/mm 3 ; hemoglobin less than 10 g/dL; neutrophil less than 750 cells/mm 3 ; platelet less than 50,000 cells/mm 3 ). Body System CHC Combination Therapy Study NV15801 PEGASYS ® 180 mcg + 1000 mg or 1200 mg Ribavirin Tablets 48 weeks Interferon alfa-2b + 1000 mg or 1200 mg REBETOL ® 48 weeks N=451 N=443 % % Application Site Disorders Injection site reaction 23 16 Endocrine Disorders Hypothyroidism 4 5 Flu-like Symptoms and Signs Fatigue/Asthenia Pyrexia Rigors Pain 65 41 25 10 68 55 37 9 Gastrointestinal Nausea/Vomiting Diarrhea Abdominal pain Dry mouth Dyspepsia 25 11 8 4 6 29 10 9 7 5 Hematologic* Lymphopenia Anemia Neutropenia Thrombocytopenia 14 11 27 5 12 11 8 <1 Metabolic and Nutritional Anorexia Weight decrease 24 10 26 10 Musculoskeletal, Connective Tissue and Bone Myalgia Arthralgia Back pain 40 22 5 49 23 5 Neurological Headache Dizziness (excluding vertigo) Memory impairment 43 14 6 49 14 5 Psychiatric Irritability/Anxiety/Nervousness Insomnia Depression Concentration impairment Mood alteration 33 30 20 10 5 38 37 28 13 6 Resistance Mechanism Disorders Overall 12 10 Respiratory, Thoracic and Mediastinal Dyspnea Cough Dyspnea exertional 13 10 4 14 7 7 Skin and Subcutaneous Tissue Alopecia Pruritus Dermatitis Dry skin Rash Sweating increased Eczema 28 19 16 10 8 6 5 33 18 13 13 5 5 4 Visual Disorders Vision blurred 5 2 Pediatric Patients In a clinical trial with 114 pediatric subjects (5 to 17 years of age) treated with PEGASYS ® alone or in combination with ribavirin, dose modifications were required in approximately one-third of subjects, most commonly for neutropenia and anemia. In general, the safety profile observed in pediatric subjects was similar to that seen in adults. In the pediatric study, the most common adverse events in subjects treated with combination therapy PEGASYS ® and ribavirin for up to 48 weeks were influenza-like illness (91%), upper respiratory tract infection (60%), headache (64%), gastrointestinal disorder (56%), skin disorder (47%), and injection-site reaction (45%). Seven subjects receiving combination PEGASYS ® and ribavirin treatment for 48 weeks discontinued therapy for safety reasons (depression, psychiatric evaluation abnormal, transient blindness, retinal exudates, hyperglycemia, type 1 diabetes mellitus, and anemia). Severe adverse events were reported in 2 subjects in the PEGASYS ® plus ribavirin combination therapy group (hyperglycemia and cholecystectomy). Table 6 Percentage of Pediatric Subjects with Adverse Reactions* During First 24 Weeks of Treatment by Treatment Group and for 24 Weeks Post-treatment (in at Least 10% of Subjects) * Displayed adverse drug reactions include all grades of reported adverse clinical events considered possibly, probably, or definitely related to study drug. ** Subjects in the PEGASYS ® plus placebo arm who did not achieve undetectable viral load at week 24 switched to combination treatment thereafter. Therefore, only the first 24 weeks are presented for the comparison of combination therapy with monotherapy. Study NV17424 System Organ Class PEGASYS ® 180 mcg/1.73 m² x BSA + Ribavirin 15 mg/kg (N=55) PEGASYS ® 180 mcg/1.73 m² x BSA + Placebo** (N=59) % % General disorders and administration site conditions Influenza like illness 91 81 Injection site reaction 44 42 Fatigue 25 20 Irritability 24 14 Gastrointestinal disorders Gastrointestinal disorder 49 44 Nervous system disorders Headache 51 39 Skin and subcutaneous tissue disorders Rash 15 10 Pruritus 11 12 Musculoskeletal, connective tissue and bone disorders Musculoskeletal pain 35 29 Psychiatric disorders Insomnia 9 12 Metabolism and nutrition disorders Decreased appetite 11 14 In pediatric subjects randomized to combination therapy, the incidence of most adverse reactions was similar for the entire treatment period (up to 48 weeks plus 24 weeks follow-up) in comparison to the first 24 weeks, and increased only slightly for headache, gastrointestinal disorder, irritability and rash. The majority of adverse reactions occurred in the first 24 weeks of treatment. Growth Inhibition in Pediatric Subjects [see Warnings and Precautions (5.8) ]. Pediatric subjects treated with PEGASYS ® plus ribavirin combination therapy showed a delay in weight and height increases with up to 48 weeks of therapy compared with baseline. Both weight for age and height for age z-scores as well as the percentiles of the normative population for subject weight and height decreased during treatment. At the end of 2 years follow-up after treatment, most subjects had returned to baseline normative curve percentiles for weight (64 th mean percentile at baseline, 60 th mean percentile at 2 years post-treatment) and height (54 th mean percentile at baseline, 56 th mean percentile at 2 years post-treatment). At the end of treatment, 43% (23 of 53) of subjects experienced a weight percentile decrease of more than 15 percentiles, and 25% (13 of 53) experienced a height percentile decrease of more than 15 percentiles on the normative growth curves. At 2 years post-treatment, 16% (6 of 38) of subjects were more than 15 percentiles below their baseline weight curve and 11% (4 of 38) were more than 15 percentiles below their baseline height curve. Thirty-eight of the 114 subjects enrolled in the long-term follow-up study, extending up to 6 years post-treatment. For most subjects, post-treatment recovery in growth at 2 years post-treatment was maintained to 6 years post-treatment. Common Adverse Reactions in CHC with HIV Coinfection (Adults) The adverse event profile of coinfected patients treated with PEGASYS ® /ribavirin in Study NR15961 was generally similar to that shown for monoinfected patients in Study NV15801 ( Table 5 ). Events occurring more frequently in coinfected patients were neutropenia (40%), anemia (14%), thrombocytopenia (8%), weight decrease (16%), and mood alteration (9%). Laboratory Test Abnormalities Adult Patients Anemia due to hemolysis is the most significant toxicity of ribavirin therapy. Anemia (hemoglobin less than 10 g/dL) was observed in 13% of all ribavirin and PEGASYS ® combination-treated patients in clinical trials. The maximum drop in hemoglobin occurred during the first 8 weeks of initiation of ribavirin therapy [see Dosage and Administration (2.3) ] . Table 7 Selected Laboratory Abnormalities During Treatment with Ribavirin in Combination With Either PEGASYS ® or Interferon alfa-2b Laboratory Parameter PEGASYS ® + Ribavirin 1000/1200 mg 48 wks Interferon alfa-2b + Ribavirin 1000/1200 mg 48 wks (N=887) (N=443) Neutrophils (cells/mm 3 ) 1,000 <1,500 34% 38% 500 <1,000 49% 21% <500 5% 1% Platelets (cells/mm 3 ) 50,000 to <75,000 11% 4% 20,000 to <50,000 5% < 1% <20,000 0 0 Hemoglobin (g/dL) 8.5 to 9.9 11% 11% <8.5 2% < 1% Pediatric Patients Decreases in hemoglobin, neutrophils and platelets may require dose reduction or permanent discontinuation from treatment [see Dosage and Administration (2.4) ]. Most laboratory abnormalities noted during the clinical trial returned to baseline levels shortly after discontinuation of treatment. Table 8 Selected Hematologic Abnormalities During First 24 Weeks of Treatment by Treatment Group in Previously Untreated Pediatric Subjects * Subjects in the PEGASYS ® plus placebo arm who did not achieve undetectable viral load at week 24 switched to combination treatment thereafter. Therefore, only the first 24 weeks are presented for the comparison of combination therapy with monotherapy. Laboratory Parameter PEGASYS ® 180 mcg/1.73 m² x BSA + Ribavirin 15 mg/kg (N=55) PEGASYS ® 180 mcg/1.73 m² x BSA + Placebo* (N=59) Neutrophils (cells/mm 3 ) 1,000 to <1,500 31% 39% 750 to <1,000 27% 17% 500 to <750 25% 15% <500 7% 5% Platelets (cells/mm 3 ) 75,000 to <100,000 4% 2% 50,000 to <75,000 0% 2% <50,000 0% 0% Hemoglobin (g/dL) 8.5 to <10 7% 3% <8.5 0% 0% In patients randomized to combination therapy, the incidence of abnormalities during the entire treatment phase (up to 48 weeks plus 24 weeks follow-up) in comparison to the first 24 weeks increased slightly for neutrophils between 500 and 1,000 cells/mm³ and hemoglobin values between 8.5 and 10 g/dL. The majority of hematologic abnormalities occurred in the first 24 weeks of treatment. 6.2 Postmarketing Experience The following adverse reactions have been identified and reported during post-approval use of PEGASYS ® /ribavirin combination therapy. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. Blood and Lymphatic System disorders Pure red cell aplasia Ear and Labyrinth disorders Hearing impairment, hearing loss Eye disorders Serous retinal detachment Immune disorders Liver and renal graft rejection Metabolism and Nutrition disorders Dehydration Skin and Subcutaneous Tissue disorders Stevens-Johnson syndrome (SJS) Toxic epidermal necrolysis (TEN)

Results from a pharmacokinetic sub-study demonstrated no pharmacokinetic interaction between PEGASYS ® (peginterferon alfa-2a) and ribavirin. Nucleoside analogues: Closely monitor for toxicities. Discontinue nucleoside reverse transcriptase inhibitors or reduce dose or discontinue interferon, ribavirin or both with worsening toxicities (7.1) Azathioprine: Concomitant use of azathioprine with ribavirin has been reported to induce severe pancytopenia and may increase the risk of azathioprine-related myelotoxicity (7.3) 7.1 Nucleoside Reverse Transcriptase Inhibitors (NRTIs) In vitro data indicate ribavirin reduces phosphorylation of lamivudine, stavudine, and zidovudine. However, no pharmacokinetic (e.g., plasma concentrations or intracellular triphosphorylated active metabolite concentrations) or pharmacodynamic (e.g., loss of HIV/HCV virologic suppression) interaction was observed when ribavirin and lamivudine (n=18), stavudine (n=10), or zidovudine (n=6) were coadministered as part of a multi-drug regimen to HCV/HIV coinfected patients. In Study NR15961 among the CHC/HIV coinfected cirrhotic patients receiving NRTIs, cases of hepatic decompensation (some fatal) were observed [see Warnings and Precautions (5.3) ] . Patients receiving PEGASYS ® /ribavirin and NRTIs should be closely monitored for treatment-associated toxicities. Physicians should refer to prescribing information for the respective NRTIs for guidance regarding toxicity management. In addition, dose reduction or discontinuation of PEGASYS ® , ribavirin or both should also be considered if worsening toxicities are observed, including hepatic decompensation (e.g., Child-Pugh greater than or equal to 6) [see Warnings and Precautions (5.3) and Dosage and Administration (2.3) ] . Didanosine Coadministration of ribavirin and didanosine is contraindicated. Didanosine or its active metabolite (dideoxyadenosine 5’-triphosphate) concentrations are increased when didanosine is coadministered with ribavirin, which could cause or worsen clinical toxicities. Reports of fatal hepatic failure as well as peripheral neuropathy, pancreatitis, and symptomatic hyperlactatemia/lactic acidosis have been reported in clinical trials [see Contraindications (4) ] . Zidovudine In Study NR15961, patients who were administered zidovudine in combination with PEGASYS ® /ribavirin developed severe neutropenia (ANC less than 500) and severe anemia (hemoglobin less than 8 g/dL) more frequently than similar patients not receiving zidovudine (neutropenia 15% vs. 9%) (anemia 5% vs. 1%). Discontinuation of zidovudine should be considered as medically appropriate. 7.2 Drugs Metabolized by Cytochrome P450 In vitro studies indicate that ribavirin does not inhibit CYP 2C9, CYP 2C19, CYP 2D6 or CYP 3A4. 7.3 Azathioprine The use of ribavirin to treat chronic hepatitis C in patients receiving azathioprine has been reported to induce severe pancytopenia and may increase the risk of azathioprine-related myelotoxicity. Inosine monophosphate dehydrogenase (IMDH) is required for one of the metabolic pathways of azathioprine. Ribavirin is known to inhibit IMDH, thereby leading to accumulation of an azathioprine metabolite, 6-methylthioinosine monophosphate (6-MTITP), which is associated with myelotoxicity (neutropenia, thrombocytopenia, and anemia). Patients receiving azathioprine with ribavirin should have complete blood counts, including platelet counts, monitored weekly for the first month, twice monthly for the second and third months of treatment, then monthly or more frequently if dosage or other therapy changes are necessary [see Warnings and Precautions (5.6) ] .