Ribavirin (RBV) in combination with pegylated interferon α (pegIFN) is the current recommended treatment of chronic hepatitis C virus (HCV) infection. The main limitation of RBV is its narrow therapeutic window. Although high RBV doses have been associated with the best chances of attaining sustained virologic responses,1,2 they also increase the risk of hemolytic anemia.3
Little is known about the influence of RBV plasma levels on early virologic response to pegIFN plus RBV. The question is relevant, because early events in HCV RNA clearance after initiation of anti-HCV therapy seem to be crucial for the final outcome.4-6 The establishment of a therapeutic window for RBV plasma levels above which the risk of anemia may be too high and below which efficacy may be significantly compromised may be of great value for the appropriate use of the drug.
Chronic hepatitis C is currently one of the main comorbidities in HIV-infected individuals.7 Treatment of hepatitis C in coinfected patients has become a priority because of the faster progression to end-stage liver disease in this population.8 Unfortunately, the success of anti-HCV therapy seems to be much lower in HCV/HIV-coinfected individuals than in HCV-monoinfected patients.7 In vitro experiments have shown a decrease in the phosphorylation of some nucleoside analogue inhibitors by RBV, although the interaction does not seem to have clinical consequences.9-11 Conversely, it is unknown whether HIV nucleoside analogue reverse transcriptase inhibitors (NRTIs) may influence RBV pharmacokinetics. Herein, we report the results of a study in which RBV plasma levels were monitored in a group of HIV/HCV-coinfected patients during the first 12 weeks of anti-HCV therapy. The primary objective of the study was to assess if early monitoring of RBV plasma levels could help to predict the development of anemia and/or the chance of attaining an early virologic response in HIV/HCV-coinfected individuals. The secondary goal was to evaluate if antiretroviral drugs might influence RBV plasma levels.
PATIENTS AND METHODS
All HIV/HCV-coinfected patients who initiated anti-HCV therapy with pegIFN-2a at a dose of 180 μg/wk plus RBV at a dose of 800 to 1200 mg/d at our institution in 2003 were included in the study. RBV doses were adjusted to body weight (bw; 1000 mg for a person weighing <75 kg and 1200 mg for a person weighing ≥75 kg). Lower doses of RBV (800 mg) were used in a few patients with a low bw (<60 kg).
Demographics and other clinical characteristics at baseline were recorded in a case report form. Hemoglobin (Hb) and creatinine (Cr) plasma levels, RBV dose, bw, and concomitant antiretroviral drugs were evaluated at baseline and at weeks 4 and 12 of therapy. Baseline creatinine clearance (CrCl) was estimated using the Cockroft-Gault equation.12 Plasma HCV RNA was measured using the Cobas Amplicor HCV Monitor, version 2.0 (Roche, Barcelona, Spain), which has a detection limit of 600 IU/mL, at baseline and at weeks 4 and 12 of therapy. Early virologic response was defined as a drop in HCV RNA of at least 2 log10 at weeks 4 and 12 compared with baseline.
Blood was drawn from patients in the morning before the intake of the first daily dose of RBV. A high-performance liquid chromatography (HPLC) method,13 with slight modifications, was used to measure RBV plasma concentrations in plasma at weeks 4 and 12.
Results are expressed in absolute values and percentages. The Student t test was used to compare quantitative variables between groups. Univariate and multivariate linear regression analyses were used to assess which factors influenced RBV plasma levels and drops in Hb. The variables influencing the early virologic response were assessed using univariate and multivariate logistic regression analyses. Receiving operating characteristic (ROC) curves were performed to calculate the sensitivity and specificity values for RBV concentrations at which higher drops in Hb and early virologic responses were more likely to occur. All statistical analyses were performed using SPSS for Windows, version 10.0 (SPSS, Chicago, IL).
A total of 98 HIV/HCV-coinfected patients were analyzed. Their main demographics and baseline biologic features are recorded in Table 1. Most were male and former intravenous drug users and were on antiretroviral therapy at the time they initiated treatment with pegIFN and RBV.
The range of RBV plasma concentrations at week 4 was from 0.45 to 4.67 μg/mL (mean ± SD: 2.71 ± 1.07 μg/mL), and the range at week 12 was from 0.73 to 4.51 μg/mL (mean ± SD: 2.72 ± 0.89 μg/mL). Although there was wide interindividual variability, there were no significant intraindividual variations in RBV concentrations comparing weeks 4 and 12 (P = 0.6). All patients had CrCl close to normal limits. As shown in Table 2, bw and CrCl did not influence RBV plasma levels. RBV dose per kilogram of bw was the only variable associated with RBV plasma levels at week 4. Results at week 12 confirmed this finding.
A mean decrease in Hb of 2.5 g/dL (range: −1-9 g/dL) was noticed at week 4, and a decrease of 2.7 g/dL (range: −1-7 g/dL) was noticed at week 12. At week 4, greater Hb declines were independently associated with higher RBV concentrations (β = 0.8, 95% confidence interval [CI]: 0.6-1.1; P < 0.001) as well as with concomitant zidovudine (ZDV) use (β = 0.8, 95% CI: 0.1-1.6; P = 0.023). RBV dosage, gender, and bw were not associated with the development of anemia. Age and RBV dose (mg/kg of bw) were correlated with anemia in the univariate analysis (P = 0.02 and P = 0.04, respectively), but the significance was lost after adjusting for other variables in the multivariate analysis. Similar results were found at week 12. Figure 1 shows the linear relation between RBV plasma concentrations and drops in Hb at week 12.
As a consequence of RBV-related anemia, 2% and 5% of patients underwent RBV dose reductions at weeks 4 and 12, respectively. None of our patients received recombinant erythropoietin.
Early virologic response (EVR) to anti-HCV therapy was obtained in 52% and 83% of patients at weeks 4 and 12, respectively. Patients who achieved EVR at week 4 had significantly higher RBV plasma levels than those who did not (3.0 vs. 2.5 μg/mL; P = 0.04). In the multivariate analysis, RBV plasma levels (odds ratio [OR] = 1.9, 95% CI: 1.2-3.2; P = 0.03) and HCV genotype 3 (OR = 52.9, 95% CI: 6.4-434.2; P < 0.001) were independent predictors of EVR at week 4 (Table 3). Similar results were obtained at week 12. No correlation was found between drops in Hb and reductions in HCV RNA levels (r = 0.2; P = 0.1).
We then examined which RBV plasma concentrations were best able to predict EVR and the development of anemia. ROC curves showed that RBV concentrations >2.8 μg/mL could help to predict drops in Hb higher than 2 g/dL with 73% sensitivity and 81% sensibility (P < 0.001). Also, with 70% sensitivity and 49% sensitivity, EVR was more likely to occur (P = 0.01) in those subjects with RBV concentrations >2.7 μg/mL.
No differences in mean RBV plasma concentrations were found comparing individuals concomitantly receiving abacavir (ABC), tenofovir (TDF), lamivudine (3TC), or stavudine (d4T) with respect to the rest. In contrast, RBV plasma levels at week 4 were significantly higher in subjects receiving ZDV compared with those not taking it (3.4 vs. 2.5 μg/mL; P = 0.002). At week 12, however, this difference was lost (2.78 vs. 2.68 μg/mL; P = 0.7). It should be noted that 5 patients (5.2%) discontinued concomitant ZDV after week 4 of anti-HCV treatment was completed.
This study shows that RBV plasma levels are widely variable among different individuals and that RBV daily dose per kilogram of bw is the main determinant of RBV plasma levels. Recent studies14-16 have reported that RBV daily dose should be based on the patient's kidney function, because that is the best determinant of RBV clearance (mainly renal). In our study population, RBV plasma concentrations were not influenced by different values of CrCl, in agreement with the results of other authors.17 Nevertheless, it is important to note that most of the subjects in our study had normal renal function, so we could not evaluate how renal insufficiency affected RBV plasma levels. In agreement with our results, some authors have highlighted the role of metabolism as the main route of elimination of RBV; <5% of the dose is eliminated in the urine.18
In contrast with the wide interindividual variability, intraindividual plasma concentrations of RBV were quite stable over time. Therefore, once the steady state is achieved, RBV plasma levels can be reliably measured once and there is no need for continuous monitoring.
As in HCV-monoinfected individuals,14,17,19 significant declines in Hb concentrations were associated with higher RBV plasma concentrations in HIV/HCV-coinfected patients. Thus, the development of RBV-induced hemolytic anemia depends primarily on RBV exposure and can be predicted by measuring RBV plasma levels. Contrary to some studies, we did not find CrCl or age to be a factor predicting anemia.20 The fact that the population in our study was characterized by narrow ranges of CrCl and age might explain the lack of association. In our population, we also found that concomitant ZDV therapy was an independent factor contributing to Hb decreases. It is well established that ZDV may reduce red cell differentiation in the bone marrow, causing anemia of central rather than peripheral origin.21 The higher RBV plasma levels in subjects receiving ZDV observed in our study may further explain the synergistic hematologic toxicity noticed in patients taking both drugs concomitantly, however.
Although RBV has been clearly proven to reduce relapses in patients receiving anti-HCV therapy, data supporting its role along with IFN during the first phases of HCV clearance have been controversial,22-25 and its mechanism of action remains largely unknown. Although RBV may act predominantly as an immunomodulatory agent, enhancing the elimination of infected hepatocytes, our finding of a significant correlation between RBV plasma levels and early virologic response may argue in favor of a direct antiviral action of the drug.26-29 RBV plasma concentrations have been shown to correlate with sustained virologic response in some studies. 13,17 To our knowledge, our results show for the first time that RBV may also play a key role along with IFN to accelerate early HCV clearance, as assessed at weeks 4 and 12 of therapy in our HIV/HCV-coinfected population. A recent Japanese study conducted in HCV-monoinfected patients also has shown that the median decrease in HCV RNA levels between weeks 2 and 12 was much more pronounced when RBV was provided along with IFN compared with using IFN alone, but that study did not measure RBV plasma concentrations.30
In HIV/HCV-coinfected patients, a potential decrease in the phosphorylation of some HIV nucleoside analogues has been a matter of concern when taking RBV concomitantly, although several reports have shown that this interaction does not seem to be clinically relevant.9-11 Little is known about a possible influence of HIV nucleoside analogues on RBV pharmacokinetics, however. Our results show a lack of effect of ABC, TDF, 3TC, and d4T on RBV plasma levels at week 4, whereas ZDV was associated with increased RBV plasma levels. The loss of an association of higher RBV levels with the use of ZDV might be explained by the discontinuation of ZDV in some patients after week 4 and/or by the reduction in RBV doses in some others. More studies are needed to confirm our findings and to elucidate their potential clinical relevance.
RBV plasma level monitoring is currently not advised in patients who initiate treatment of chronic hepatitis C with pegIFN plus RBV, except in patients with renal insufficiency.15 Nevertheless, our results point out the potential usefulness of this measure to improve responses with a minimal impact on Hb levels. We found a threshold in RBV plasma levels above which early HCV clearance was more pronounced and below which the risk of anemia was significantly higher. Those cutoffs are too close, according to our results. Therefore, to achieve a response to treatment, the patients are placed at high risk for developing severe anemia. We can use the results of RBV level monitoring at week 4 to individually tailor RBV dosages and the use of recombinant erythropoietin to manage anemia, however. In that regard, recent studies in HCV-monoinfected subjects receiving combination therapy have reported maintenance of RBV dosages and Hb levels thanks to the use of epoetin.31
Further studies are needed to verify our findings in larger populations. Given that therapeutic drug monitoring of antiretroviral drugs is steadily expanding as a useful tool for optimizing antiretroviral therapy,32 RBV measurements early after initiating anti-HCV therapy might be equally advised.
In summary, RBV plasma levels at weeks 4 and 12 were found to correlate with enhanced HCV RNA clearance and the development of anemia in HIV/HCV-coinfected subjects treated with pegIFN and RBV. In addition, a possible interaction between RBV and ZDV was noticed, resulting in increased plasma RBV levels at week 4, which might further contribute to exacerbate anemia. Because RBV plasma levels seem to be quite stable over time, their monitoring shortly after initiation of anti-HCV therapy might help to adjust RBV dosages and improve their efficacy as well as aiding in the management of toxicity of anti-HCV therapy in HIV/HCV-coinfected patients.
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