- Email: [email protected]
Ribavirin pharmacokinetics in renal and liver transplant patients: evidence that it depends on renal function
Ribavirin Pharmacokinetics in Renal and Liver Transplant Patients: Evidence That It Depends on Renal Function Nassim Kamar, MD, Etienne Chatelut, PharmD, PhD, Efthymios Manolis, PharmD, Thierry Lafont, Jacques Izopet, PharmD, PhD, and Lionel Rostaing, MD, PhD ● Background: Ribavirin is approved for the treatment of chronic hepatitis C virus (HCV) infection. However, no recommendation exists for dosing patients with impaired renal function. Methods: The authors performed a pharmacokinetic study in 21 HCV-positive renal or liver transplant patients. The mean creatinine clearance (ClCr) calculated by the Cockcroft–Gault equation was 57 mL/min (0.95 mL/s; range, 17 to 89 mL/min [0.28 to 1.48 mL/s]). Twelve blood samples were obtained during a 96-hour period after the first single administration of 1,000 mg of ribavirin. After the first pharmacokinetics (PK) and the pharmacodynamics (PD) profile was completed, the patients received ribavirin at 1,000 mg/d with or without interferon-␣. A blood sample was taken monthly just before the oral administration of ribavirin. Plasma ribavirin concentrations were determined by high-performance liquid chromatography. Results: A total of 428 plasma concentrations were analyzed by a population pharmacokinetic method using the NONlinear Mixed Effect Model program. The mean observed ribavirin apparent clearance (CL/F) was 9.1 L/h (with an interindividual variability of 39%). The influences of the age, sex, body weight (BW), serum creatinine (Scr), ClCr, hemoglobin, and graft status on CL/F were examined. CL/F was highly correlated with ClCr (r ⴝ 0.63, P < 0.01). The final regression formula was CL/F (L/h) ⴝ 32.3 ⴛ BW ⴛ (1 ⴚ 0.0094 ⴛ age) ⴛ (1 ⴚ 0.42 ⴛ sex)/Scr, where sex ⴝ 0 for men and 1 for women; Scr is in micromoles per liter. Sex had a larger influence on CL/F than that corresponding to the Cockcroft–Gault equation (ie, 15%). Conclusion: The authors present the parameters that determine ribavirin clearance in HCV(ⴙ) transplant patients with normal or impaired renal function. Moreover, we suggest ribavirin daily doses according to various levels of renal function. Am J Kidney Dis 43:140-146. © 2004 by the National Kidney Foundation, Inc. INDEX WORDS: Ribavirin pharmacokinetics; renal function; hepatitis C virus (HCV); renal-transplant patients; liver-transplant patients.
IBAVIRIN (1--D-ribofuranosyl-1,2,4-triazole-3-carboxyamide), a guanosine analogue, inhibits the replication of a wide range of RNA and DNA viruses, including those of the flavivirus family, of which hepatitis C virus (HCV) is a member.1 Ribavirin is normally eliminated by renal filtration. Therefore, in cases of renal failure it accumulates, particularly in red blood cells. Thus, hemolytic anemia is one of the main side effects. According to the manufacturer, ribavirin therapy is contraindicated when creatinine clearance (CrCl) is lower than 50 mL/min (0.83 mL/s). The prevalence of HCV infection is high in renal allograft recipients, ranging from 10% to 50% in the United States,2 resulting in signifi-
R
From the Department of Nephrology, Dialysis and Transplantation, CHU Rangueil, Institut Claudius Regaud, and Department of Virology, CHU Purpan, Toulouse, France. Received July 24, 2003; accepted in revised form September 23, 2003. Address reprint requests to Professor L. Rostaing, Department of Nephrology, Dialysis and Transplantation, CHU Rangueil, TSA 50032, 31059 Toulouse Cedex 9, France. E-mail: [email protected] © 2004 by the National Kidney Foundation, Inc. 0272-6386/04/4301-0015$30.00/0 doi:10.1053/j.ajkd.2003.09.019 140
cantly lower long-term patient and graft survival rates compared with HCV-negative (⫺) renal transplant patients.3,4 Moreover, HCV infection might contribute to the occurrence of both de novo glomerulonephritis as well as chronic allograft nephropathy.5,6 In HCV-positive (⫹) renal transplant patients (1) interferon-␣ (IFN-␣) therapy is contraindicated because it results in cellular and/or humoral acute rejection7-9 without any virologic effect, and (2) ribavirin therapy alone has been assessed in only 2 studies so far.10,11 One of the most frequent indications of liver transplantation is HCV-related cirrhosis. The recurrence on the graft is the rule. Even if there is no short-term detrimental effect, it might alter the long-term outcome.12 In HCV(⫹) liver transplants, the combined IFN-␣/ribavirin therapy seems to induce virologic remissions, even if side effects are high, eg, anemia.13 Recently, Jain et al14 reported that liver transplant patients who were taking IFN-␣ and ribavirin and who experienced hemolysis, had significantly higher serum creatinine levels and lower CrCls compared with those who did not have hemolysis. The investigators suggested that pharmacokinetics studies should be performed to determine the safer use
American Journal of Kidney Diseases, Vol 43, No 1 (January), 2004: pp 140-146
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of ribavirin in HCV(⫹) patients. The aim of our study was to assess the parameters that determine the pharmacokinetic profile of ribavirin in transplant patients with mild to moderate impairment of their renal function and, accordingly, to suggest adapted daily doses of ribavirin. PATIENTS Twenty-one patients, 14 renal and 7 liver transplant patients, were included in the ribavirin pharmacokinetic study according to following criteria: (1) renal or liver transplantation for more than 12 months, (2) HCV RNA positive, (3) a recent liver biopsy result showing evidence for HCV-related liver disease requiring an anti-HCV therapy, and (4) patients who gave their written informed consent to participate to the study. The protocol was approved by our local ethics committee.
METHODS
Biological Assessments at Baseline HCV RNA viremia, liver enzymes (aspartate aminotransferase [AST], alanine aminotransferase [ALT], and gammaglutamyl transpeptidase [␥-GT]), serum creatinine, proteinuria, hemoglobin level, platelet and white blood cell counts, haptoglobin, and lactate dehydrogenase (LDH) levels were assessed in all patients at baseline and then monthly after the initiation of anti-HCV therapy.
Anti-HCV Therapy Because it has been shown that IFN-␣ is associated with cellular and/or humoral rejection in renal transplant patients, the renal recipients received ribavirin monotherapy. Conversely, the liver transplant patients were given a combined antiviral therapy including IFN-␣ plus ribavirin. However, before the patients took any antiviral therapy they underwent a ribavirin pharmacokinetic profile, ie, at hour 0 each patient was given 5 capsules of ribavirin (1,000 mg). During the following 96 hours, the pharmacokinetic profile was performed. Thereafter, the antiviral therapy was started (see below).
Blood Samples and High-Performance Liquid Chromatography Determination of Plasma Ribavirin Concentrations After the very first dose of 1,000 mg of ribavirin, the pharmacokinetic profile was measured. Blood samples were taken on EDTA tubes at hours 0 (just before) and at 1, 2, 3, 4, 6, 9, 12, 24, 36, 48, 72, and 96 hours after the first dose. Blood samples were taken monthly just before and 2 hours after the oral administration. Plasma ribavirin concentrations were determined using a previously published high-performance liquid chromatography (HPLC) method15 with some modifications. Briefly, plasma samples were prepared by adding 0.5 mL of the specimen to 0.5 mL of buffer ammonium phosphate (250 mmol/L, pH 8.8) and 400 L (0.067 mol/L) of 3-methylcytidine methosulfate (the internal standard). Solid phase extraction was performed using a Polyprep
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Bio-Rad column with Affi-gel 601 media (Bio-Rad Laboratoiries, Inc, Hercules, CA). Regarding the chromatographic conditions, the mobile phase consisted of ammonium phosphate buffer (10 mmol/L) adjusted to pH 4.8, and the flow rate was 1 mL/min. Separation was achieved on a Bischoff Nucleosil C18 7- (0.46 by 25 cm) column, and ultraviolet detection was performed at a wave length of 215 nm. The average within-run and between-runs precision was less than 10% for all quality control samples. The average accuracies were within 87% and 118%.
Pharmacokinetic Analysis The data analysis was performed according to a population pharmacokinetic approach using the NONMEM (NONlinear Mixed Effect Model) program (version V, level 1.1) and the first-order conditional estimation (FOCE) method. The basic pharmacokinetic model was a first-order absorption, 2-compartment model with a first-order elimination from the central compartment. The objective of the analysis was to evaluate the relationships between ribavirin clearance (CL) and the patients’ covariates: age, sex, body weight, serum creatinine level, Cockcroft–Gault CrCl, hemoglobin level, and graft status. In analyzing the data, NONMEM computed the value of a statistical function: the minimal value of the objective function (OFV). The difference between OFV for the 2 models is approximately 2 distributed. A covariate was considered as significantly correlated with CL when a decrease of greater than 3.8 (corresponding to P ⬍ 0.05) of OFV was associated with the addition of the covariate within the covariate model for clearance.
Statistical Analysis Hematologic and renal parameters are expressed as mean ⫾ SD, and liver and hemolysis parameters are expressed as median (ranges). Quantitative variables were analyzed using the unpaired t test. A P value below 0.05 was considered statistically significant.
RESULTS
Patients’ Demographics at Baseline Fifteen men and 6 women of a median age of 58 years (range, 27 to 73) were included in the ribavirin pharmacokinetic study. All of them were HCV RNA positive with evidence for HCVrelated liver disease; hence, the mean Knodell score was 10.2 ⫾ 1.2. Liver enzymes showed AST at 62 U/L (range, 17 to 350 U/L), ALT at 125 U/L (range, 31 to 419 U/L), and ␥-GT at 87 U/L (13 to 637 U/L). The HCV genotype was 1b in 11 cases, 2a in 4 cases, 3a in 2 cases, 4 in 2 cases, 2 in one case, and 1 in the last case. The mean HCV RNA viremia was 5.8 ⫾ 0.1 log copies/mL. Immunosuppression was based either on cyclosporin A (12 patients ) or on tacrolimus (7 cases); the last 2 patients received azathioprine and steroids. Renal function was mildly
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impaired: the mean (⫾ SD) serum creatinine was 1.54 ⫾ 0.72 mg/dL (range, 0.87 to 3.21 mg/dL; 136 ⫾ 64 mol/L [range, 77 to 284 mol/L]), ie, a Cockcroft–Gault calculated CrCl at 57.0 ⫾ 20.0 mL/min (0.95 ⫾ 0.33 mL/s) (range, 17 to 89 mL/min [0.28 to 1.48 mL/s]). CrCl was lower than 50 mL/min (0.83 mL/s) in 7 patients, greater than 80 mL/min (1.33 mL/s) in only 3 patients, and between 50 and 80 mL/min (between 0.83 and 1.33 mL/s) in the remaining 11 patients. Nine patients had significant proteinuria, with a median at 0.368 g/L (range, 0.16 to 0.78). At baseline, the mean hemoglobin level was 13.5 ⫾ 1.5 g/dL (135 ⫾ 15 g/L). There was no evidence of hemolysis, ie, haptoglobin level was 90 mg/dL (1 g/L; range, 25 to 154 mg/dL [0 to 2 g/L]), and LDH level was 518 U/L (range, 308 to 1,017 U/L). White blood cells and platelet counts were, respectively, 4.8 ⫻ 103/L (range, 2.9 to 10.6 ⫻ 103/L [⫻109/L]) and 175 ⫻ 103/L (range, 79 to 378 ⫻ 103/L [⫻109/L]). Clinical Data at Follow-Up After 1 year of antiviral treatment, there was a significant decrease in AST (28.5 [range, 14 to 80] versus 62 [range, 17 to 350] U/L; P ⫽ 0.0037), ALT (40 [range, 18 to 142] versus 125 [range, 31 to 419] U/L; P ⫽ 0.0002), and ␥-GT (51.5 [range, 14 to 219] versus 87 [range, 13 to 637) U/L; P ⫽ 0.0033) levels. After 1 year of ribavirin therapy, only 4 patients of 9 remained with significant proteinuria, respectively, 0.3, 0.35, 0.43 and 1.25 g/L. With respect to the hematologic tolerance, compared with baseline, there was a significant decrease in the hemoglobin levels as early as 2 weeks after initiation of ribavirin therapy, ie, 11.7 ⫾ 1.5 g/dL (117 ⫾ 15 g/L) versus 13.5 ⫾ 1.5 g/dL (135 ⫾ 15 g/L; P ⬍ 0.001). The decrease in hemoglobin levels persisted 1 month (10.5 ⫾ 2.3 g/dL [105 ⫾ 23 g/L]; P ⬍ 0.001), 3 months (10.9 ⫾ 1.9 g/dL [109 ⫾ 19 g/L]; P ⬍ 0.001), and 1 year (12.4 ⫾ 1.5 g/dL [124 ⫾ 15 g/L]; P ⫽ 0.004) after the initiation of ribavirin therapy despite recombinant erythropoietin support. However, compared with baseline values, we did not observe significant changes in LDH levels. Conversely, compared with baseline values, there was a progressive decrease in haptoglobin levels, which was highly significant 1 year after the initiation of the treatment: 90 mg/dL (1 g/L; 25 to 154 mg/dL [0 to 2 g/L]) at
KAMAR ET AL
baseline; 78 mg/dL (5 to 221 mg/dL [0 to 2 g/L]) at day 15, P value, not significant; 66 mg/dL (10 to 169 mg/dL [0 to 2 g/L]) at 1 month, P value, not significant; 44 mg/dL (10 to 259 mg/dL [0 to 3 g/L]) at 3 months, P value, not significant; and 7.5 mg/dL (6 to 105 mg/dL [0 to 1 g/L]) at 1 year, P ⫽ 0.0004. Pharmacokinetics A total of 428 plasma concentrations were available. Data at steady state (at least 2 weeks of ribavirin administrations) were available for 14 patients. The raw data are shown in Fig 1A and 1B. At steady state the mean ribavirin trough levels were 2,387 ⫾ 827 mg/mL, whereas the mean concentrations 2 hours after ribavirin administration were 3,136 ⫾ 944 mg/mL. The 2-compartment model with first-order absorption and first-order elimination correctly described the ribavirin plasma concentrations versus time. Mean pharmacokinetic parameters were determined using a basic model (model without covariate). They are shown in Table 1. Clearance and volumes of distribution are apparent parameters, because bioavailability could not be assessed. There was a strong correlation between post-hoc Bayesian-estimated CL and Cockcroft–Gault CrCl (Fig 2). The more complete covariate model tested was: CL ⫽ 1 ⫻ (1 ⫺ 2 ⫻ age) ⫻ (1 ⫺ 3 ⫻ sex) ⫻ BW/Scr ⫹ 4 ⫻ BW with BW for body weight, sex ⫽ 0 if a man or 1 if a woman, and Scr for serum creatinine (mol/L). Presence of the nonrenal function-dependent factor (ie, 4 ⫻ BW or 4) did not improve the model. Sex had a larger influence on CL/F than that corresponding to the Cockcroft–Gault equation (ie, 15%). The best covariate model is shown in Table 2 and is compared with alternative models. By considering the final model, interindividual variability on CL decreased from 39% (no covariate) to 17% (final covariate model). The objective function value corresponding to the model based on Cockcroft–Gault CrCl (ie, CL ⫽ 1⫹ 2 ⫻ CrCl) was not significantly larger than that of the final model. Moreover, the coefficients provided by NONMEM analysis were
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Fig 1. Ribavirin concentrations versus time for the whole data set (B), and truncated at 96 hours to show concentrations after the first 1000-mg dose (A). Empty squares for ribavirin trough levels; filled squares for ribavirin concentrations 2 hours after intake.
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Table 1.
Pharmacokinetic Parameters of Ribavirin in 21 Patients
Cockcroft–Gault CrCls and CLs, are presented in Table 3. For example, when renal function is normal and targeting a steady-state level of 10 mol/L, the daily dose of ribavirin should be 810 mg, ie, 4 tablets. Conversely, for the same target but when renal function is impaired, ie, a CrCl at 20 mL/min (0.33 mL/s), the daily dose should be 330 mg.
Parameter
Mean (⫾ 95% CI*)
CV%†
CL/F‡ (clearance) V1/F (central volume of distribution) Q/F (intercompartmental clearance) V2/F (peripheral volume of distribution) Ka (absorption rate constant)
9.06 L/h (⫾ 1.87)
39%
799 L (⫾ 537)
31%
123 L/h (⫾ 87.2)
65%
DISCUSSION
2730 L (⫾ 566)
43%
0.70 h⫺1 (⫾ 0.59)
15%
The prevalence of hepatitis C virus infection is increasing in the general population. In certain groups, such as hemodialysis patients and transplant recipients (liver, kidney), its prevalence could be as high as 60%. Moreover, it negatively affects the patients’ survival rates. Its current treatment relies on a dual therapy, ie, IFN-␣ and ribavirin. Because the latter might result in severe hematologic side effects when the renal function is impaired, we performed a pharmacokinetic profile study to refine its use in this setting. Relationships between ribavirin plasma concentrations and pharmacodynamics have already been observed,16 both with toxicity and activity; the hemoglobin nadir corresponding to the dose-limiting toxicity was negatively associated with ribavirin concentrations,17 and higher concentrations were associated with a higher antiviral response rate.18 To date, the dosing recommendations are based only on patients’ body weight. Moreover, Jen et al17 proposed to monitor hemoglobin concentrations during treat-
*Confidence interval (␣ ⫽ 5%) corresponding to the precision. †Coefficient of variation for interindividual variability. ‡Apparent parameters because bioavailability (F) was not assessable.
consistent with those corresponding to the regression coefficients between post-hoc Bayesian CLs as shown in Fig 2: 1 ⫽ 2.2 versus 3.6 (corresponding to the nonrenal CL) and 2 ⫽ 0.111 versus 0.103. We then attempted to establish the optimal daily doses of ribavirin for 2 given ribavirin steady-state mean levels, ie, 10 and 14 mol/L (2.44 and 3.42 g/mL, respectively) and for different levels of renal function ranging from normal, ie, a CrCl of 100 mL/min (1.67 mL/s), to severely impaired (20 mL/min [0.33 mL/s]). The daily doses of ribavirin, suggested by the relationship we obtained between
Fig 2. Correlation between ribavirin plasma clearance and Cockcroft–Gault CrCl. To convert CrCl in mL/ min to mL/s, multiply by 0.01667.
RIBAVIRIN PHARMACOKINETICS AND RENAL FUNCTION Table 2.
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Final Covariate Model for CL
Final Covariate Model
CL (L/h) ⫽ 1 ⫻ (1 ⫺ 2 ⫻ age) ⫻ (1 ⫺ 3 ⫻ sex) ⫻ BW/Scr with BW for body weight, age in years, sex ⫽ 0 if male, 1 if female, and Scr for serum creatinine in mol/L Alternative Covariate Models
CL ⫽ 1 ⫻ (1 ⫺ 2 ⫻ age) ⫻ (1 ⫺ 3 ⫻ sex) (independent of the ratio BW/Scr) CL ⫽ 1 ⫻ BW ⫻ (1 ⫺ 3 ⫻ sex)/Scr (independent of age) CL ⫽ 1 ⫻ BW ⫻ (1 ⫺ 2 ⫻ age)/Scr (independent of sex) CL (L/h) ⫽ 1 ⫹ 2 ⫻ CrCl with CrCl for Cockcroft-Gault CrCl (mL/min)
Mean (⫾ 95% CI*)
%CV
1 ⫽ 32.3 (⫾ 6.9) 2 ⫽ 0.0094 (⫾ 0.0024) 3 ⫽ 0.42 (⫾ 0.16)
17
⌬OBJ
P
%CV
⫹11.9 ⫹12.2 ⫹5.5 ⫹3.6
⬍0.01 ⬍0.01 ⬍0.05 NS
34 30 21 23
Abbreviations: %CV, coefficient of variation for inter-individual variability not explained by the covariates; ⌬OBJ, change in objective function by comparison with the final model; NS, not significant. *Confidence interval (␣ ⫽ 5%) corresponding to the precision.
ment and to adjust the ribavirin dose accordingly. Lastly, the actual recommendation consists of considering that impaired renal function is the only contraindication of the drug. As previously shown by Bruchfeld et al19 the results of the current study show that renal function, and CrCl in particular, should be taken into account for ribavirin dosing. Although the number of patients included in this pharmacokinetic study was limited, we observed a strong relationship between CrCl and CL. Moreover, the final covariate model we obtained included the same covariates as those of the Cockcroft–Gault equation. Lastly, it is very important to note that the regression equation between CL and CrCl was consistent with that reported by Bruchfeld et al19: CL ⫽ 3.6 ⫹ 0.103 ⫻ CrCl versus CL ⫽ 0.0414 ⫻ BW ⫹ 0.122 ⫻ CrCl, respectively. The only difference is that we did not manage to observe a significant link between nonrenal clearance and body weight; this was probably because of the lower number of patients in our study. Thus, the suggestions made by Bruchfeld et al19 for the daily Table 3. Daily Doses (mg) for Different Target Ribavirin Concentrations According to the Cockcroft-Gault CrCl CrCl (mL/min) Target Css
100
80
60
40
20
10 mol/L 14 mol/L
810 1140
690 970
570 800
450 630
330 460
NOTE. To convert CrCl in mL/min to mL/s, multiply by 0.01667.
starting doses of ribavirin are validated by our results. Recently, Larrat et al18 have observed a mean ribavirin concentration of 2.67 g/mL in 24 HCV-(⫹) patients with normal renal function who were treated with this drug. This is why we chose 2 targets of ribavirin in our model: 1 below and 1 above this concentration. Our first target is a ribavirin concentration of 2.44 g/mL, ie, 10 mol/L. The second ribavirin target is higher and corresponds to the upper concentration values reported in the article by Bruchfeld et al.19 Thus, given these 2 targets, and for a given level of renal function, we propose adapted daily ribavirin doses to limit the side effects, eg, hemolytic anemia. Because the half-life of ribavirin that corresponded to the mean pharmacokinetic parameters (ie, CL/F, V1/F, and V2/F) we observed in our 21 patients was 11 days instead of 6 days in patients with normal renal function,20 we may wonder why a twice-daily schedule has been selected for a drug with such a long half-life, particularly in patients with impaired renal function. Therefore, using our results, for a patient with a CrCl of 20 mL/min (0.33 mL/s) and targeting a steady-state mean concentration of 10 mol/L, the daily dose of ribavirin will be 330 mg (daily dose of 400 mg for 2 days out of 3, and 200 mg the other day). Interferon-␣ monotherapy is not efficient and is harmful in HCV(⫹) renal transplant patients because it may induce acute renal failure.21 Therefore, in this population with either HCV-related liver damage and/or HCV-related de novo glomerulopathies the clinician is left with ribavirin therapy. This is contra-
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indicated when CrCl is lower than 50 mL/min (0.83 mL/s) because its accumulation might result in severe hemolytic anemia. It has been reported recently that ribavirin monotherapy was able to induce sustained proteinuria remission both in liver22 and renal11 transplant patients. In addition, a combination of IFN-␣ and ribavirin has also been reported to be efficient in the treatment of interferon-resistant immunocompetent patients with HCV-related glomerulopathy.23 In this study, we hope to give clinicians data for the efficient and safe appropriate dosage for ribavirin according to renal function assessed by the Cockcroft–Gault equation. We present the parameters that determine CL in HCV(⫹) transplant patients with normal or impaired renal function. These results are confirmatory of those previously published by Bruchfeld et al.19 Moreover, we propose daily doses of ribavirin according to various levels of renal function, with the aim of achieving steady state ribavirin levels of 10 or 14 mol/L. REFERENCES 1. Patterson JL, Fernandez-Larsson R: Molecular mechanisms of action of ribavirin. Rev Infect Dis 12:1139-1146, 1990 2. Fabrizi F, Martin P, Ponticelli C: Hepatitis C virus infection and renal transplantation. Am J Kidney Dis 38:919934, 2001 3. Legendre C, Garrigue V, Le Bihan C, et al: Harmful long-term impact of hepatitis C virus infection in kidney transplant recipients. Transplantation 65:667-670, 1998 4. Mathurin P, Mouquet C, Poynard T, et al: Impact of hepatitis B and C virus on kidney transplantation outcome. Hepatology 29:257-263, 1999 5. Morales JM, Campistol JM, Andres A, Rodicio JL: Hepatitis C virus and renal transplantation. Curr Opin Nephrol Hypertens 7:117-183, 1998 6. Cosio FG, Sedmak DD, Henry ML, et al: The high prevalence of severe early posttransplant renal allograft pathology in hepatitis C positive recipients. Transplantation 62:1054-1059, 1996 7. Thervet E, Pol S, Legendre C, Gagnadoux MF, Cavalcanti R, Kreis H: Low-dose recombinant leukocyte interferonalpha treatment of hepatitis C viral infection in renal transplant recipients. A pilot study. Transplantation 58:625-628, 1994 8. Rostaing L, Izopet J, Baron E, Duffaut M, Puel J, Durand D: Treatment of chronic hepatitis C with recombinant interferon alpha in kidney transplant recipients. Transplantation 59:1426-1431, 1995 9. Baid S, Tolkoff-Rubin N, Saidman S, et al: Acute hu-
moral rejection in hepatitis C-infected renal transplant recipients receiving antiviral therapy. Am J Transplant 3:74-78, 2003 10. Garnier JL, Chevallier P, Dubernard JM, Trepo C, Touraine JL, Chossegros P: Treatment of hepatitis C virus infection with ribavirin in kidney transplant patients. Transplant Proc 29:783, 1997 11. Kamar N, Sandres-Saune K, Selves J, et al: Longterm ribavirin therapy in hepatitis C virus positive renal transplant patients: Effects upon renal function and liver histology. Am J Kidney Dis 42:184-192, 2003 12. Terrault NA: Hepatitis C virus and liver transplantation. Semin Gastrointest Dis 11:96-114, 2000 13. Gane EJ, Lo SK, Riordan SM, et al: A randomized study comparing ribavirin and interferon alpha monotherapy for hepatitis C recurrence after liver transplantation. Hepatology 27:1403-1407, 1998 14. Jain AB, Eghtesad B, Venkataramanan R, et al: Ribavirin dose modification based on renal function is necessary to reduce hemolysis in liver transplant patients with hepatitis C virus infection. Liver Transpl 8:1007-1013, 2002 15. Granich GG, Krogstad DJ, Connor JD, Desrochers KL, Sherwood C: High-performance liquid chromatography (HPLC) assay for ribavirin and comparison of the HPLC assay with radioimmunoassay. Antimicrob Agents Chemother 33:311-315, 1989 16. Jen J, Laughlin M, Chung C, et al: Ribavirin dosing in chronic hepatitis C: Application of population pharmacokinetic-pharmacodynamic models. Clin Pharmacol Ther 72: 349-361, 2002 17. Jen JF, Glue P, Gupta S, Zambas D, Hajian G: Population pharmacokinetic and pharmacodynamic analysis of ribavirin in patients with chronic hepatitis C. Ther Drug Monit 22:555-565, 2000 18. Larrat S, Stanke-Labesque F, Plages A, Zarski JP, Bessard G, Souvignet C: Ribavirin quantification in combination treatment of chronic hepatitis C. Antimicrob Agents Chemother 47:124-129, 2003 19. Bruchfeld A, Lindahl K, Schvarcz R, Stahle L: Dosage of ribavirin in patients with hepatitis C should be based on renal function: A population pharmacokinetic analysis. Ther Drug Monit 24:701-708, 2002 20. Morse GD, Shelton MJ, O’Donnell AM: Comparative pharmacokinetics of antiviral nucleoside analogues. Clin Pharmacokinet 24:101-123, 1993 21. Rostaing L, Izopet J, Baron E, et al: Preliminary results of treatment of chronic hepatitis C with recombinant interferon alpha in renal transplant patients. Nephrol Dial Transplant 10:93-96, 1995 22. Pham HP, Feray C, Samuel D, et al: Effects of ribavirin on hepatitis C-associated nephrotic syndrome in four liver transplant recipients. Kidney Int 54:1311-1319, 1998 23. Sabry AA, Sobh MA, Sheaashaa HA, et al: Effect of combination therapy (ribavirin and interferon) in HCV-related glomerulopathy. Nephrol Dial Transplant 17:1924-1930, 2002
IBAVIRIN (1--D-ribofuranosyl-1,2,4-triazole-3-carboxyamide), a guanosine analogue, inhibits the replication of a wide range of RNA and DNA viruses, including those of the flavivirus family, of which hepatitis C virus (HCV) is a member.1 Ribavirin is normally eliminated by renal filtration. Therefore, in cases of renal failure it accumulates, particularly in red blood cells. Thus, hemolytic anemia is one of the main side effects. According to the manufacturer, ribavirin therapy is contraindicated when creatinine clearance (CrCl) is lower than 50 mL/min (0.83 mL/s). The prevalence of HCV infection is high in renal allograft recipients, ranging from 10% to 50% in the United States,2 resulting in signifi-
R
From the Department of Nephrology, Dialysis and Transplantation, CHU Rangueil, Institut Claudius Regaud, and Department of Virology, CHU Purpan, Toulouse, France. Received July 24, 2003; accepted in revised form September 23, 2003. Address reprint requests to Professor L. Rostaing, Department of Nephrology, Dialysis and Transplantation, CHU Rangueil, TSA 50032, 31059 Toulouse Cedex 9, France. E-mail: [email protected] © 2004 by the National Kidney Foundation, Inc. 0272-6386/04/4301-0015$30.00/0 doi:10.1053/j.ajkd.2003.09.019 140
cantly lower long-term patient and graft survival rates compared with HCV-negative (⫺) renal transplant patients.3,4 Moreover, HCV infection might contribute to the occurrence of both de novo glomerulonephritis as well as chronic allograft nephropathy.5,6 In HCV-positive (⫹) renal transplant patients (1) interferon-␣ (IFN-␣) therapy is contraindicated because it results in cellular and/or humoral acute rejection7-9 without any virologic effect, and (2) ribavirin therapy alone has been assessed in only 2 studies so far.10,11 One of the most frequent indications of liver transplantation is HCV-related cirrhosis. The recurrence on the graft is the rule. Even if there is no short-term detrimental effect, it might alter the long-term outcome.12 In HCV(⫹) liver transplants, the combined IFN-␣/ribavirin therapy seems to induce virologic remissions, even if side effects are high, eg, anemia.13 Recently, Jain et al14 reported that liver transplant patients who were taking IFN-␣ and ribavirin and who experienced hemolysis, had significantly higher serum creatinine levels and lower CrCls compared with those who did not have hemolysis. The investigators suggested that pharmacokinetics studies should be performed to determine the safer use
American Journal of Kidney Diseases, Vol 43, No 1 (January), 2004: pp 140-146
RIBAVIRIN PHARMACOKINETICS AND RENAL FUNCTION
of ribavirin in HCV(⫹) patients. The aim of our study was to assess the parameters that determine the pharmacokinetic profile of ribavirin in transplant patients with mild to moderate impairment of their renal function and, accordingly, to suggest adapted daily doses of ribavirin. PATIENTS Twenty-one patients, 14 renal and 7 liver transplant patients, were included in the ribavirin pharmacokinetic study according to following criteria: (1) renal or liver transplantation for more than 12 months, (2) HCV RNA positive, (3) a recent liver biopsy result showing evidence for HCV-related liver disease requiring an anti-HCV therapy, and (4) patients who gave their written informed consent to participate to the study. The protocol was approved by our local ethics committee.
METHODS
Biological Assessments at Baseline HCV RNA viremia, liver enzymes (aspartate aminotransferase [AST], alanine aminotransferase [ALT], and gammaglutamyl transpeptidase [␥-GT]), serum creatinine, proteinuria, hemoglobin level, platelet and white blood cell counts, haptoglobin, and lactate dehydrogenase (LDH) levels were assessed in all patients at baseline and then monthly after the initiation of anti-HCV therapy.
Anti-HCV Therapy Because it has been shown that IFN-␣ is associated with cellular and/or humoral rejection in renal transplant patients, the renal recipients received ribavirin monotherapy. Conversely, the liver transplant patients were given a combined antiviral therapy including IFN-␣ plus ribavirin. However, before the patients took any antiviral therapy they underwent a ribavirin pharmacokinetic profile, ie, at hour 0 each patient was given 5 capsules of ribavirin (1,000 mg). During the following 96 hours, the pharmacokinetic profile was performed. Thereafter, the antiviral therapy was started (see below).
Blood Samples and High-Performance Liquid Chromatography Determination of Plasma Ribavirin Concentrations After the very first dose of 1,000 mg of ribavirin, the pharmacokinetic profile was measured. Blood samples were taken on EDTA tubes at hours 0 (just before) and at 1, 2, 3, 4, 6, 9, 12, 24, 36, 48, 72, and 96 hours after the first dose. Blood samples were taken monthly just before and 2 hours after the oral administration. Plasma ribavirin concentrations were determined using a previously published high-performance liquid chromatography (HPLC) method15 with some modifications. Briefly, plasma samples were prepared by adding 0.5 mL of the specimen to 0.5 mL of buffer ammonium phosphate (250 mmol/L, pH 8.8) and 400 L (0.067 mol/L) of 3-methylcytidine methosulfate (the internal standard). Solid phase extraction was performed using a Polyprep
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Bio-Rad column with Affi-gel 601 media (Bio-Rad Laboratoiries, Inc, Hercules, CA). Regarding the chromatographic conditions, the mobile phase consisted of ammonium phosphate buffer (10 mmol/L) adjusted to pH 4.8, and the flow rate was 1 mL/min. Separation was achieved on a Bischoff Nucleosil C18 7- (0.46 by 25 cm) column, and ultraviolet detection was performed at a wave length of 215 nm. The average within-run and between-runs precision was less than 10% for all quality control samples. The average accuracies were within 87% and 118%.
Pharmacokinetic Analysis The data analysis was performed according to a population pharmacokinetic approach using the NONMEM (NONlinear Mixed Effect Model) program (version V, level 1.1) and the first-order conditional estimation (FOCE) method. The basic pharmacokinetic model was a first-order absorption, 2-compartment model with a first-order elimination from the central compartment. The objective of the analysis was to evaluate the relationships between ribavirin clearance (CL) and the patients’ covariates: age, sex, body weight, serum creatinine level, Cockcroft–Gault CrCl, hemoglobin level, and graft status. In analyzing the data, NONMEM computed the value of a statistical function: the minimal value of the objective function (OFV). The difference between OFV for the 2 models is approximately 2 distributed. A covariate was considered as significantly correlated with CL when a decrease of greater than 3.8 (corresponding to P ⬍ 0.05) of OFV was associated with the addition of the covariate within the covariate model for clearance.
Statistical Analysis Hematologic and renal parameters are expressed as mean ⫾ SD, and liver and hemolysis parameters are expressed as median (ranges). Quantitative variables were analyzed using the unpaired t test. A P value below 0.05 was considered statistically significant.
RESULTS
Patients’ Demographics at Baseline Fifteen men and 6 women of a median age of 58 years (range, 27 to 73) were included in the ribavirin pharmacokinetic study. All of them were HCV RNA positive with evidence for HCVrelated liver disease; hence, the mean Knodell score was 10.2 ⫾ 1.2. Liver enzymes showed AST at 62 U/L (range, 17 to 350 U/L), ALT at 125 U/L (range, 31 to 419 U/L), and ␥-GT at 87 U/L (13 to 637 U/L). The HCV genotype was 1b in 11 cases, 2a in 4 cases, 3a in 2 cases, 4 in 2 cases, 2 in one case, and 1 in the last case. The mean HCV RNA viremia was 5.8 ⫾ 0.1 log copies/mL. Immunosuppression was based either on cyclosporin A (12 patients ) or on tacrolimus (7 cases); the last 2 patients received azathioprine and steroids. Renal function was mildly
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impaired: the mean (⫾ SD) serum creatinine was 1.54 ⫾ 0.72 mg/dL (range, 0.87 to 3.21 mg/dL; 136 ⫾ 64 mol/L [range, 77 to 284 mol/L]), ie, a Cockcroft–Gault calculated CrCl at 57.0 ⫾ 20.0 mL/min (0.95 ⫾ 0.33 mL/s) (range, 17 to 89 mL/min [0.28 to 1.48 mL/s]). CrCl was lower than 50 mL/min (0.83 mL/s) in 7 patients, greater than 80 mL/min (1.33 mL/s) in only 3 patients, and between 50 and 80 mL/min (between 0.83 and 1.33 mL/s) in the remaining 11 patients. Nine patients had significant proteinuria, with a median at 0.368 g/L (range, 0.16 to 0.78). At baseline, the mean hemoglobin level was 13.5 ⫾ 1.5 g/dL (135 ⫾ 15 g/L). There was no evidence of hemolysis, ie, haptoglobin level was 90 mg/dL (1 g/L; range, 25 to 154 mg/dL [0 to 2 g/L]), and LDH level was 518 U/L (range, 308 to 1,017 U/L). White blood cells and platelet counts were, respectively, 4.8 ⫻ 103/L (range, 2.9 to 10.6 ⫻ 103/L [⫻109/L]) and 175 ⫻ 103/L (range, 79 to 378 ⫻ 103/L [⫻109/L]). Clinical Data at Follow-Up After 1 year of antiviral treatment, there was a significant decrease in AST (28.5 [range, 14 to 80] versus 62 [range, 17 to 350] U/L; P ⫽ 0.0037), ALT (40 [range, 18 to 142] versus 125 [range, 31 to 419] U/L; P ⫽ 0.0002), and ␥-GT (51.5 [range, 14 to 219] versus 87 [range, 13 to 637) U/L; P ⫽ 0.0033) levels. After 1 year of ribavirin therapy, only 4 patients of 9 remained with significant proteinuria, respectively, 0.3, 0.35, 0.43 and 1.25 g/L. With respect to the hematologic tolerance, compared with baseline, there was a significant decrease in the hemoglobin levels as early as 2 weeks after initiation of ribavirin therapy, ie, 11.7 ⫾ 1.5 g/dL (117 ⫾ 15 g/L) versus 13.5 ⫾ 1.5 g/dL (135 ⫾ 15 g/L; P ⬍ 0.001). The decrease in hemoglobin levels persisted 1 month (10.5 ⫾ 2.3 g/dL [105 ⫾ 23 g/L]; P ⬍ 0.001), 3 months (10.9 ⫾ 1.9 g/dL [109 ⫾ 19 g/L]; P ⬍ 0.001), and 1 year (12.4 ⫾ 1.5 g/dL [124 ⫾ 15 g/L]; P ⫽ 0.004) after the initiation of ribavirin therapy despite recombinant erythropoietin support. However, compared with baseline values, we did not observe significant changes in LDH levels. Conversely, compared with baseline values, there was a progressive decrease in haptoglobin levels, which was highly significant 1 year after the initiation of the treatment: 90 mg/dL (1 g/L; 25 to 154 mg/dL [0 to 2 g/L]) at
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baseline; 78 mg/dL (5 to 221 mg/dL [0 to 2 g/L]) at day 15, P value, not significant; 66 mg/dL (10 to 169 mg/dL [0 to 2 g/L]) at 1 month, P value, not significant; 44 mg/dL (10 to 259 mg/dL [0 to 3 g/L]) at 3 months, P value, not significant; and 7.5 mg/dL (6 to 105 mg/dL [0 to 1 g/L]) at 1 year, P ⫽ 0.0004. Pharmacokinetics A total of 428 plasma concentrations were available. Data at steady state (at least 2 weeks of ribavirin administrations) were available for 14 patients. The raw data are shown in Fig 1A and 1B. At steady state the mean ribavirin trough levels were 2,387 ⫾ 827 mg/mL, whereas the mean concentrations 2 hours after ribavirin administration were 3,136 ⫾ 944 mg/mL. The 2-compartment model with first-order absorption and first-order elimination correctly described the ribavirin plasma concentrations versus time. Mean pharmacokinetic parameters were determined using a basic model (model without covariate). They are shown in Table 1. Clearance and volumes of distribution are apparent parameters, because bioavailability could not be assessed. There was a strong correlation between post-hoc Bayesian-estimated CL and Cockcroft–Gault CrCl (Fig 2). The more complete covariate model tested was: CL ⫽ 1 ⫻ (1 ⫺ 2 ⫻ age) ⫻ (1 ⫺ 3 ⫻ sex) ⫻ BW/Scr ⫹ 4 ⫻ BW with BW for body weight, sex ⫽ 0 if a man or 1 if a woman, and Scr for serum creatinine (mol/L). Presence of the nonrenal function-dependent factor (ie, 4 ⫻ BW or 4) did not improve the model. Sex had a larger influence on CL/F than that corresponding to the Cockcroft–Gault equation (ie, 15%). The best covariate model is shown in Table 2 and is compared with alternative models. By considering the final model, interindividual variability on CL decreased from 39% (no covariate) to 17% (final covariate model). The objective function value corresponding to the model based on Cockcroft–Gault CrCl (ie, CL ⫽ 1⫹ 2 ⫻ CrCl) was not significantly larger than that of the final model. Moreover, the coefficients provided by NONMEM analysis were
RIBAVIRIN PHARMACOKINETICS AND RENAL FUNCTION
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Fig 1. Ribavirin concentrations versus time for the whole data set (B), and truncated at 96 hours to show concentrations after the first 1000-mg dose (A). Empty squares for ribavirin trough levels; filled squares for ribavirin concentrations 2 hours after intake.
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Table 1.
Pharmacokinetic Parameters of Ribavirin in 21 Patients
Cockcroft–Gault CrCls and CLs, are presented in Table 3. For example, when renal function is normal and targeting a steady-state level of 10 mol/L, the daily dose of ribavirin should be 810 mg, ie, 4 tablets. Conversely, for the same target but when renal function is impaired, ie, a CrCl at 20 mL/min (0.33 mL/s), the daily dose should be 330 mg.
Parameter
Mean (⫾ 95% CI*)
CV%†
CL/F‡ (clearance) V1/F (central volume of distribution) Q/F (intercompartmental clearance) V2/F (peripheral volume of distribution) Ka (absorption rate constant)
9.06 L/h (⫾ 1.87)
39%
799 L (⫾ 537)
31%
123 L/h (⫾ 87.2)
65%
DISCUSSION
2730 L (⫾ 566)
43%
0.70 h⫺1 (⫾ 0.59)
15%
The prevalence of hepatitis C virus infection is increasing in the general population. In certain groups, such as hemodialysis patients and transplant recipients (liver, kidney), its prevalence could be as high as 60%. Moreover, it negatively affects the patients’ survival rates. Its current treatment relies on a dual therapy, ie, IFN-␣ and ribavirin. Because the latter might result in severe hematologic side effects when the renal function is impaired, we performed a pharmacokinetic profile study to refine its use in this setting. Relationships between ribavirin plasma concentrations and pharmacodynamics have already been observed,16 both with toxicity and activity; the hemoglobin nadir corresponding to the dose-limiting toxicity was negatively associated with ribavirin concentrations,17 and higher concentrations were associated with a higher antiviral response rate.18 To date, the dosing recommendations are based only on patients’ body weight. Moreover, Jen et al17 proposed to monitor hemoglobin concentrations during treat-
*Confidence interval (␣ ⫽ 5%) corresponding to the precision. †Coefficient of variation for interindividual variability. ‡Apparent parameters because bioavailability (F) was not assessable.
consistent with those corresponding to the regression coefficients between post-hoc Bayesian CLs as shown in Fig 2: 1 ⫽ 2.2 versus 3.6 (corresponding to the nonrenal CL) and 2 ⫽ 0.111 versus 0.103. We then attempted to establish the optimal daily doses of ribavirin for 2 given ribavirin steady-state mean levels, ie, 10 and 14 mol/L (2.44 and 3.42 g/mL, respectively) and for different levels of renal function ranging from normal, ie, a CrCl of 100 mL/min (1.67 mL/s), to severely impaired (20 mL/min [0.33 mL/s]). The daily doses of ribavirin, suggested by the relationship we obtained between
Fig 2. Correlation between ribavirin plasma clearance and Cockcroft–Gault CrCl. To convert CrCl in mL/ min to mL/s, multiply by 0.01667.
RIBAVIRIN PHARMACOKINETICS AND RENAL FUNCTION Table 2.
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Final Covariate Model for CL
Final Covariate Model
CL (L/h) ⫽ 1 ⫻ (1 ⫺ 2 ⫻ age) ⫻ (1 ⫺ 3 ⫻ sex) ⫻ BW/Scr with BW for body weight, age in years, sex ⫽ 0 if male, 1 if female, and Scr for serum creatinine in mol/L Alternative Covariate Models
CL ⫽ 1 ⫻ (1 ⫺ 2 ⫻ age) ⫻ (1 ⫺ 3 ⫻ sex) (independent of the ratio BW/Scr) CL ⫽ 1 ⫻ BW ⫻ (1 ⫺ 3 ⫻ sex)/Scr (independent of age) CL ⫽ 1 ⫻ BW ⫻ (1 ⫺ 2 ⫻ age)/Scr (independent of sex) CL (L/h) ⫽ 1 ⫹ 2 ⫻ CrCl with CrCl for Cockcroft-Gault CrCl (mL/min)
Mean (⫾ 95% CI*)
%CV
1 ⫽ 32.3 (⫾ 6.9) 2 ⫽ 0.0094 (⫾ 0.0024) 3 ⫽ 0.42 (⫾ 0.16)
17
⌬OBJ
P
%CV
⫹11.9 ⫹12.2 ⫹5.5 ⫹3.6
⬍0.01 ⬍0.01 ⬍0.05 NS
34 30 21 23
Abbreviations: %CV, coefficient of variation for inter-individual variability not explained by the covariates; ⌬OBJ, change in objective function by comparison with the final model; NS, not significant. *Confidence interval (␣ ⫽ 5%) corresponding to the precision.
ment and to adjust the ribavirin dose accordingly. Lastly, the actual recommendation consists of considering that impaired renal function is the only contraindication of the drug. As previously shown by Bruchfeld et al19 the results of the current study show that renal function, and CrCl in particular, should be taken into account for ribavirin dosing. Although the number of patients included in this pharmacokinetic study was limited, we observed a strong relationship between CrCl and CL. Moreover, the final covariate model we obtained included the same covariates as those of the Cockcroft–Gault equation. Lastly, it is very important to note that the regression equation between CL and CrCl was consistent with that reported by Bruchfeld et al19: CL ⫽ 3.6 ⫹ 0.103 ⫻ CrCl versus CL ⫽ 0.0414 ⫻ BW ⫹ 0.122 ⫻ CrCl, respectively. The only difference is that we did not manage to observe a significant link between nonrenal clearance and body weight; this was probably because of the lower number of patients in our study. Thus, the suggestions made by Bruchfeld et al19 for the daily Table 3. Daily Doses (mg) for Different Target Ribavirin Concentrations According to the Cockcroft-Gault CrCl CrCl (mL/min) Target Css
100
80
60
40
20
10 mol/L 14 mol/L
810 1140
690 970
570 800
450 630
330 460
NOTE. To convert CrCl in mL/min to mL/s, multiply by 0.01667.
starting doses of ribavirin are validated by our results. Recently, Larrat et al18 have observed a mean ribavirin concentration of 2.67 g/mL in 24 HCV-(⫹) patients with normal renal function who were treated with this drug. This is why we chose 2 targets of ribavirin in our model: 1 below and 1 above this concentration. Our first target is a ribavirin concentration of 2.44 g/mL, ie, 10 mol/L. The second ribavirin target is higher and corresponds to the upper concentration values reported in the article by Bruchfeld et al.19 Thus, given these 2 targets, and for a given level of renal function, we propose adapted daily ribavirin doses to limit the side effects, eg, hemolytic anemia. Because the half-life of ribavirin that corresponded to the mean pharmacokinetic parameters (ie, CL/F, V1/F, and V2/F) we observed in our 21 patients was 11 days instead of 6 days in patients with normal renal function,20 we may wonder why a twice-daily schedule has been selected for a drug with such a long half-life, particularly in patients with impaired renal function. Therefore, using our results, for a patient with a CrCl of 20 mL/min (0.33 mL/s) and targeting a steady-state mean concentration of 10 mol/L, the daily dose of ribavirin will be 330 mg (daily dose of 400 mg for 2 days out of 3, and 200 mg the other day). Interferon-␣ monotherapy is not efficient and is harmful in HCV(⫹) renal transplant patients because it may induce acute renal failure.21 Therefore, in this population with either HCV-related liver damage and/or HCV-related de novo glomerulopathies the clinician is left with ribavirin therapy. This is contra-
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indicated when CrCl is lower than 50 mL/min (0.83 mL/s) because its accumulation might result in severe hemolytic anemia. It has been reported recently that ribavirin monotherapy was able to induce sustained proteinuria remission both in liver22 and renal11 transplant patients. In addition, a combination of IFN-␣ and ribavirin has also been reported to be efficient in the treatment of interferon-resistant immunocompetent patients with HCV-related glomerulopathy.23 In this study, we hope to give clinicians data for the efficient and safe appropriate dosage for ribavirin according to renal function assessed by the Cockcroft–Gault equation. We present the parameters that determine CL in HCV(⫹) transplant patients with normal or impaired renal function. These results are confirmatory of those previously published by Bruchfeld et al.19 Moreover, we propose daily doses of ribavirin according to various levels of renal function, with the aim of achieving steady state ribavirin levels of 10 or 14 mol/L. REFERENCES 1. Patterson JL, Fernandez-Larsson R: Molecular mechanisms of action of ribavirin. Rev Infect Dis 12:1139-1146, 1990 2. Fabrizi F, Martin P, Ponticelli C: Hepatitis C virus infection and renal transplantation. Am J Kidney Dis 38:919934, 2001 3. Legendre C, Garrigue V, Le Bihan C, et al: Harmful long-term impact of hepatitis C virus infection in kidney transplant recipients. Transplantation 65:667-670, 1998 4. Mathurin P, Mouquet C, Poynard T, et al: Impact of hepatitis B and C virus on kidney transplantation outcome. Hepatology 29:257-263, 1999 5. Morales JM, Campistol JM, Andres A, Rodicio JL: Hepatitis C virus and renal transplantation. Curr Opin Nephrol Hypertens 7:117-183, 1998 6. Cosio FG, Sedmak DD, Henry ML, et al: The high prevalence of severe early posttransplant renal allograft pathology in hepatitis C positive recipients. Transplantation 62:1054-1059, 1996 7. Thervet E, Pol S, Legendre C, Gagnadoux MF, Cavalcanti R, Kreis H: Low-dose recombinant leukocyte interferonalpha treatment of hepatitis C viral infection in renal transplant recipients. A pilot study. Transplantation 58:625-628, 1994 8. Rostaing L, Izopet J, Baron E, Duffaut M, Puel J, Durand D: Treatment of chronic hepatitis C with recombinant interferon alpha in kidney transplant recipients. Transplantation 59:1426-1431, 1995 9. Baid S, Tolkoff-Rubin N, Saidman S, et al: Acute hu-
moral rejection in hepatitis C-infected renal transplant recipients receiving antiviral therapy. Am J Transplant 3:74-78, 2003 10. Garnier JL, Chevallier P, Dubernard JM, Trepo C, Touraine JL, Chossegros P: Treatment of hepatitis C virus infection with ribavirin in kidney transplant patients. Transplant Proc 29:783, 1997 11. Kamar N, Sandres-Saune K, Selves J, et al: Longterm ribavirin therapy in hepatitis C virus positive renal transplant patients: Effects upon renal function and liver histology. Am J Kidney Dis 42:184-192, 2003 12. Terrault NA: Hepatitis C virus and liver transplantation. Semin Gastrointest Dis 11:96-114, 2000 13. Gane EJ, Lo SK, Riordan SM, et al: A randomized study comparing ribavirin and interferon alpha monotherapy for hepatitis C recurrence after liver transplantation. Hepatology 27:1403-1407, 1998 14. Jain AB, Eghtesad B, Venkataramanan R, et al: Ribavirin dose modification based on renal function is necessary to reduce hemolysis in liver transplant patients with hepatitis C virus infection. Liver Transpl 8:1007-1013, 2002 15. Granich GG, Krogstad DJ, Connor JD, Desrochers KL, Sherwood C: High-performance liquid chromatography (HPLC) assay for ribavirin and comparison of the HPLC assay with radioimmunoassay. Antimicrob Agents Chemother 33:311-315, 1989 16. Jen J, Laughlin M, Chung C, et al: Ribavirin dosing in chronic hepatitis C: Application of population pharmacokinetic-pharmacodynamic models. Clin Pharmacol Ther 72: 349-361, 2002 17. Jen JF, Glue P, Gupta S, Zambas D, Hajian G: Population pharmacokinetic and pharmacodynamic analysis of ribavirin in patients with chronic hepatitis C. Ther Drug Monit 22:555-565, 2000 18. Larrat S, Stanke-Labesque F, Plages A, Zarski JP, Bessard G, Souvignet C: Ribavirin quantification in combination treatment of chronic hepatitis C. Antimicrob Agents Chemother 47:124-129, 2003 19. Bruchfeld A, Lindahl K, Schvarcz R, Stahle L: Dosage of ribavirin in patients with hepatitis C should be based on renal function: A population pharmacokinetic analysis. Ther Drug Monit 24:701-708, 2002 20. Morse GD, Shelton MJ, O’Donnell AM: Comparative pharmacokinetics of antiviral nucleoside analogues. Clin Pharmacokinet 24:101-123, 1993 21. Rostaing L, Izopet J, Baron E, et al: Preliminary results of treatment of chronic hepatitis C with recombinant interferon alpha in renal transplant patients. Nephrol Dial Transplant 10:93-96, 1995 22. Pham HP, Feray C, Samuel D, et al: Effects of ribavirin on hepatitis C-associated nephrotic syndrome in four liver transplant recipients. Kidney Int 54:1311-1319, 1998 23. Sabry AA, Sobh MA, Sheaashaa HA, et al: Effect of combination therapy (ribavirin and interferon) in HCV-related glomerulopathy. Nephrol Dial Transplant 17:1924-1930, 2002