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Mechanism of Action
Ribavirin is an antiviral drug [see Microbiology].
Multiple dose ribavirin pharmacokinetic data are available for HCV patients who received ribavirin in combination with peginterferon alfa-2a. Following administration of 1200 mg/day with food for 12 weeks mean±SD (n=39; body weight greater than 75 kg) AUC0-12hr was 25,361±7110 ng·hr/mL and Cmax was 2748±818 ng/mL. The average time to reach Cmax was 2 hours. Trough ribavirin plasma concentrations following 12 weeks of dosing with food were 1662±545 ng/mL in HCV infected patients who received 800 mg/day (n=89), and 2112±810 ng/mL in patients who received 1200 mg/day (n=75; body weight greater than 75 kg).
The terminal half-life of ribavirin following administration of a single oral dose of COPEGUS is about 120 to 170 hours. The total apparent clearance following administration of a single oral dose of COPEGUS is about 26 L/h. There is extensive accumulation of ribavirin after multiple dosing (twice daily) such that the Cmax at steady state was four-fold higher than that of a single dose.
Effect of Food on Absorption of Ribavirin
Bioavailability of a single oral dose of ribavirin was increased by co-administration with a high-fat meal. The absorption was slowed (Tmax was doubled) and the AUC0-192h and Cmax increased by 42% and 66%, respectively, when COPEGUS was taken with a high-fat meal compared with fasting conditions [see DOSAGE AND ADMINISTRATION and PATIENT INFORMATION].
Elimination and Metabolism
The contribution of renal and hepatic pathways to ribavirin elimination after administration of COPEGUS is not known. In vitro studies indicate that ribavirin is not a substrate of CYP450 enzymes.
A clinical trial evaluated 50 CHC subjects with either moderate (creatinine clearance 30 to 50 mL/min) or severe (creatinine clearance less than 30 mL/min) renal impairment or end stage renal disease (ESRD) requiring chronic hemodialysis (HD). The apparent clearance of ribavirin was reduced in subjects with creatinine clearance less than or equal to 50 mL/min, including subjects with ESRD on HD, exhibiting approximately 30% of the value found in subjects with normal renal function. Pharmacokinetic modeling and simulation indicates that a dose of 200 mg daily in patients with severe renal impairment and a dose of 200 mg daily alternating with 400 mg the following day in patients with moderate renal impairment will provide plasma ribavirin exposures similar to that observed in patients with normal renal function receiving the standard 1000/1200 mg COPEGUS daily dose. These doses have not been studied in patients.
In 18 subjects with ESRD receiving chronic HD, COPEGUS was administered at a dose of 200 mg daily. Ribavirin plasma exposures in these subjects were approximately 20% lower compared to subjects with normal renal function receiving the standard 1000/1200 mg COPEGUS daily dose [see DOSAGE AND ADMINISTRATION, Use In Specific Populations].
Plasma ribavirin is removed by hemodialysis with an extraction ratio of approximately 50%; however, due to the large volume of distribution of ribavirin, plasma exposure is not expected to change with hemodialysis.
Mechanism of Action
The mechanism by which ribavirin contributes to its antiviral efficacy in the clinic is not fully understood. Ribavirin has direct antiviral activity in tissue culture against many RNA viruses. Ribavirin increases the mutation frequency in the genomes of several RNA viruses and ribavirin triphosphate inhibits HCV polymerase in a biochemical reaction.
Antiviral Activity in Cell Culture
In the stable HCV cell culture model system (HCV replicon), ribavirin inhibited autonomous HCV RNA replication with a 50% effective concentration (EC50) value of 11-21 mcM. In the same model, PEG-IFN α-2a also inhibited HCV RNA replication, with an EC50 value of 0.1-3 ng/mL. The combination of PEG-IFN α-2a and ribavirin was more effective at inhibiting HCV RNA replication than either agent alone.
Different HCV genotypes display considerable clinical variability in their response to PEG-IFN-α and ribavirin therapy. Viral genetic determinants associated with the variable response have not been definitively identified.
Cross-resistance between IFN α and ribavirin has not been observed.
In a study in rats, it was concluded that dominant lethality was not induced by ribavirin at doses up to 200 mg/kg for 5 days (up to 1.7 times the maximum recommended human dose of ribavirin).
Long-term studies in the mouse and rat (18 to 24 months; dose 20 to 75, and 10 to 40 mg/kg/day, respectively, approximately 0.1 to 0.4 times the maximum daily human dose of ribavirin) have demonstrated a relationship between chronic ribavirin exposure and an increased incidence of vascular lesions (microscopic hemorrhages) in mice. In rats, retinal degeneration occurred in controls, but the incidence was increased in ribavirin-treated rats.
Chronic Hepatitis C Patients
The safety and effectiveness of PEGASYS in combination with COPEGUS for the treatment of hepatitis C virus infection were assessed in two randomized controlled clinical trials. All patients were adults, had compensated liver disease, detectable hepatitis C virus, liver biopsy diagnosis of chronic hepatitis, and were previously untreated with interferon. Approximately 20% of patients in both studies had compensated cirrhosis (Child-Pugh class A). Patients coinfected with HIV were excluded from these studies.
In Study NV15801, patients were randomized to receive either PEGASYS 180 mcg subcutaneous once weekly with an oral placebo, PEGASYS 180 mcg once weekly with COPEGUS 1000 mg by mouth (body weight less than 75 kg) or 1200 mg by mouth (body weight greater than or equal to 75 kg) or interferon alfa-2b 3 MIU subcutaneous three times a week plus ribavirin 1000 mg or 1200 mg by mouth. All patients received 48 weeks of therapy followed by 24 weeks of treatment-free follow-up. COPEGUS or placebo treatment assignment was blinded. Sustained virological response was defined as undetectable (less than 50 IU/mL) HCV RNA on or after study week 68. PEGASYS in combination with COPEGUS resulted in a higher SVR compared to PEGASYS alone or interferon alfa-2b and ribavirin (Table 9). In all treatment arms, patients with viral genotype 1, regardless of viral load, had a lower response rate to PEGASYS in combination with COPEGUS compared to patients with other viral genotypes.
Table 9 : Sustained Virologic Response (SVR) to Combination
Therapy (Study NV15801)
|Interferon alfa-2b + Ribavirin 1000 mg or 1200 mg||PEGASYS + placebo||PEGASYS + COPEGUS 1000 mg or 1200 mg|
|All patients||197/444 (44%)||65/224 (29%)||241/453 (53%)|
|Genotype 1||103/285 (36%)||29/145 (20%)||132/298 (44%)|
|Genotypes 2-6||94/159 (59%)||36/79 (46%)||109/155 (70%)|
Difference in overall treatment response (PEGASYS/COPEGUS – Interferon alfa-2b/ribavirin) was 9% (95% CI 2.3, 15.3).
In Study NV15942, all patients received PEGASYS 180 mcg subcutaneous once weekly and were randomized to treatment for either 24 or 48 weeks and to a COPEGUS dose of either 800 mg or 1000 mg/1200 mg (for body weight less than 75 kg/greater than or equal to 75 kg). Assignment to the four treatment arms was stratified by viral genotype and baseline HCV viral titer. Patients with genotype 1 and high viral titer (defined as greater than 2 x 106 HCV RNA copies/mL serum) were preferentially assigned to treatment for 48 weeks.
Sustained Virologic Response (SVR) and HCV Genotype
HCV 1 and 4-Irrespective of baseline viral titer, treatment for 48 weeks with PEGASYS and 1000 mg or 1200 mg of COPEGUS resulted in higher SVR (defined as undetectable HCV RNA at the end of the 24-week treatment-free follow-up period) compared to shorter treatment (24 weeks) and/or 800 mg COPEGUS.
HCV 2 and 3-Irrespective of baseline viral titer, treatment for 24 weeks with PEGASYS and 800 mg of COPEGUS resulted in a similar SVR compared to longer treatment (48 weeks) and/or 1000 mg or 1200 mg of COPEGUS (see Table 10).
The numbers of patients with genotype 5 and 6 were too few to allow for meaningful assessment.
Table 10 : Sustained Virologic Response as a Function
of Genotype (Study NV15942)
|24 Weeks Treatment||48 Weeks Treatment|
|PEGASYS + COPEGUS 800 mg
|PEGASYS + COPEGUS 1000 mg or 1200 mg*
|PEGASYS + COPEGUS 800 mg
|PEGASYS + COPEGUS 1000 mg or 1200 mg*
|Genotype 1||29/101 (29%)||48/118 (41%)||99/250 (40%)||138/271 (51%)|
|Genotypes 2, 3||79/96 (82%)||116/144 (81%)||75/99 (76%)||117/153 (76%)|
|Genotype 4||0/5 (0%)||7/12 (58%)||5/8 (63%)||9/11 (82%)|
|*1000 mg for body weight less than 75 kg; 1200 mg for body weight greater than or equal to 75 kg.|
Previously untreated pediatric subjects 5 through 17 years of age (55% less than 12 years old) with chronic hepatitis C, compensated liver disease and detectable HCV RNA were treated with COPEGUS approximately 15 mg/kg/day plus PEGASYS 180 mcg/1.73 m² x body surface area once weekly for 48 weeks. All subjects were followed for 24 weeks post-treatment. Sustained virological response (SVR) was defined as undetectable (less than 50 IU/mL) HCV RNA on or after study week 68. A total of 114 subjects were randomized to receive either combination treatment of COPEGUS plus PEGASYS or PEGASYS monotherapy; subjects failing PEGASYS monotherapy at 24 weeks or later could receive open-label COPEGUS plus PEGASYS. The initial randomized arms were balanced for demographic factors; 55 subjects received initial combination treatment of COPEGUS plus PEGASYS and 59 received PEGASYS plus placebo; in the overall intent-to-treat population, 45% were female, 80% were Caucasian, and 81% were infected with HCV genotype 1. The SVR results are summarized in Table 11.
Table 11 : Sustained
Virologic Response (Study NV17424)
|PEGASYS 180 mcg/1.73 mē x BSA + COPEGUS 15 mg/kg*
|PEGASYS 180 mcg/1.73 mē x BSA + Placebo*
|All HCV genotypes**||29 (53%)||12 (20%)|
|HCV genotype 1||21/45 (47%)||8/47 (17%)|
|HCV non-genotype 1***||8/10 (80%)||4/12 (33%)|
|*Results indicate undetectable
HCV-RNA defined as HCV RNA less than 50 IU/mL at 24 weeks post-treatment using
the AMPLICOR HCV test v2
**Scheduled treatment duration was 48 weeks regardless of the genotype
***Includes HCV genotypes 2,3 and others
Other Treatment Response Predictors
Treatment response rates are lower in patients with poor prognostic factors receiving pegylated interferon alpha therapy. In studies NV15801 and NV15942, treatment response rates were lower in patients older than 40 years (50% vs. 66%), in patients with cirrhosis (47% vs. 59%), in patients weighing over 85 kg (49% vs. 60%), and in patients with genotype 1 with high vs. low viral load (43% vs. 56%). African-American patients had lower response rates compared to Caucasians.
In studies NV15801 and NV15942, lack of early virologic response by 12 weeks (defined as HCV RNA undetectable or greater than 2 log10 lower than baseline) was grounds for discontinuation of treatment. Of patients who lacked an early viral response by 12 weeks and completed a recommended course of therapy despite a protocol-defined option to discontinue therapy, 5/39 (13%) achieved an SVR. Of patients who lacked an early viral response by 24 weeks, 19 completed a full course of therapy and none achieved an SVR.
Chronic Hepatitis C/HIV Coinfected Patients
In Study NR15961, patients with CHC/HIV were randomized to receive either PEGASYS 180 mcg subcutaneous once weekly plus an oral placebo, PEGASYS 180 mcg once weekly plus COPEGUS 800 mg by mouth daily or interferon alfa-2a, 3 MIU subcutaneous three times a week plus COPEGUS 800 mg by mouth daily. All patients received 48 weeks of therapy and sustained virologic response (SVR) was assessed at 24 weeks of treatment-free follow-up. COPEGUS or placebo treatment assignment was blinded in the PEGASYS treatment arms. All patients were adults, had compensated liver disease, detectable hepatitis C virus, liver biopsy diagnosis of chronic hepatitis C, and were previously untreated with interferon. Patients also had CD4+ cell count greater than or equal to 200 cells/mm³ or CD4+ cell count greater than or equal to 100 cells/mm³ but less than 200 cells/mm³ and HIV-1 RNA less than 5000 copies/mL, and stable status of HIV. Approximately 15% of patients in the study had cirrhosis. Results are shown in Table 12.
Table 12 : Sustained
Virologic Response in Patients With Chronic Hepatitis C Coinfected With HIV
|Interferon alfa-2a + COPEGUS 800 mg
|PEGASYS + Placebo
|PEGASYS + COPEGUS 800 mg
|All patients||33 (11%)||58 (20%)||116 (40%)|
|Genotype 1||12/171 (7%)||24/175 (14%)||51/176 (29%)|
|Genotypes 2, 3||18/89 (20%)||32/90 (36%)||59/95 (62%)|
Treatment response rates were lower in CHC/HIV patients with poor prognostic factors (including HCV genotype 1, HCV RNA greater than 800,000 IU/mL, and cirrhosis) receiving pegylated interferon alpha therapy.
Of the patients who did not demonstrate either undetectable HCV RNA or at least a 2 log10 reduction from baseline in HCV RNA titer by 12 weeks of PEGASYS and COPEGUS combination therapy, 2% (2/85) achieved an SVR.
In CHC patients with HIV coinfection who received 48 weeks of PEGASYS alone or in combination with COPEGUS treatment, mean and median HIV RNA titers did not increase above baseline during treatment or 24 weeks post treatment.
Last reviewed on RxList: 3/4/2013
This monograph has been modified to include the generic and brand name in many instances.
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