Andrea Calcagno

Maraviroc is a substrate for OATP1B1 in vitro and maraviroc plasma concentrations are influenced by SLCO1B1 521 T>C polymorphism

Background Organic anion transporting polypeptides (OATPs) are emerging as major determinants of pharmacokinetics for numerous drugs, with the 1B1 isoform-mediating hepatic uptake. The 521 T>C polymorphism has been correlated earlier with higher plasma concentrations of several drugs and the aim of this study was to determine whether this polymorphism influences trough concentrations of maraviroc. Methods The uptake of maraviroc by OATP1B1 was assessed using a heterologous Xenopus laevis oocyte expression system and quantified using a novel liquid chromatography-mass spectrometry method. Regression analyses were conducted to identify factors associated with maraviroc Ctrough in 59 patients treated with maraviroc at 150, 300, or 600 mg twice daily. Results Maraviroc was identified as a substrate for OATP1B1 with a Km of 33.9 &mgr;mol/l. A dose of 600 mg of etravirine or efavirenz [odds ratio (OR)=0.22, 95% confidence interval (95% CI): 0.06–0.76; P=0.016] and SLCO1B1 521 heterozygosity were both associated with maraviroc Ctrough, above the suggested target concentration of 50 ng/ml (OR=20.3, 95% CI: 2.2–182; P=0.007). Conclusion These findings show the importance of OATP1B1 for variability in maraviroc pharmacokinetics. Furthermore, the SLCO1B1 521 T>C polymorphism maybe useful in predicting higher plasma concentrations but these data should be confirmed before prospective clinical studies to define the clinical usefulness.

Inosine triphosphatase polymorphisms and ribavirin pharmacokinetics as determinants of ribavirin-associate anemia in patients receiving standard anti-HCV treatment.

Background Functional variants of inosine triphosphatase (ITPA) were recently found to protect against ribavirin (RBV)-induced hemolytic anemia. However, no definitive data are yet available on the role of plasma RBV concentrations on hemoglobin (Hb) decrement. Moreover, no data have been published on the possible interplay between these 2 factors. Methods A retrospective analysis included 167 patients. The ITPA variants rs7270101 and rs1127354 were genotyped and tested using the &khgr;2 test for association with Hb reduction at week 4. We also investigated, using multivariate logistic regression, the impact of RBV plasma exposure on Hb concentrations. Results Both single nucleotide polymorphisms were associated with Hb decrease. The carrier of at least 1 variant allele in the functional ITPA single nucleotide polymorphisms was associated with a lower decrement of Hb (−1.1 g/dL), as compared with patients without a variant allele (−2.75 g/dL; P = 4.09 × 10−8). RBV concentrations were not influenced by ITPA genotypes. A cut-off of 2.3 &mgr;g/mL of RBV was found to be associated with anemia (area-under-receiver operating characteristic = 0.630, sensitivity = 50.0%, and specificity = 69.5%, P = 0.008). In multivariate logistic regression analyses, the carrier of a variant allele (P = 0.005) and plasma RBV concentrations <2.3 &mgr;g/mL (P = 0.016) were independently associated with protection against clinically significant anemia at week 4. Conclusions Although no direct relationship was found between ITPA polymorphisms and plasma RBV concentrations, both factors were shown to be significantly associated with anemia. A multivariate regression model based on ITPA genetic polymorphisms and RBV trough concentration was developed for predicting the risk of anemia. By relying upon these 2 variables, an individualized management of anemia seems to be feasible in recipients of pegylated interferon–RBV therapy.

Determinants of darunavir cerebrospinal fluid concentrations: impact of once-daily dosing and pharmacogenetics.

Objectives:To compare cerebrospinal fluid (CSF) darunavir and ritonavir concentrations in patients receiving darunavir/ritonavir 800/100 mg once daily or 600/100 mg twice daily. To determine the influence of single-nucleotide polymorphisms in the genes encoding for blood–brain barrier transporters (ABCB1 3435 C>T, ABCB1 1236 C>T, ABCB1 2677 G>T, SLCO1A2 38 A>G, SLCO1A2 516 A>C, ABCC2 -24 G>A) on darunavir and ritonavir penetration into CSF. Design:Comparative pharmacokinetics study in patients. Methods:Plasma and CSF darunavir and ritonavir concentrations (2–26 h after drug intake) were determined by a validated HPLC coupled with mass spectrometry method in adults on darunavir-based combination antiretroviral therapy undergoing a lumbar puncture. Results:HIV-infected patients on once-daily darunavir/ritonavir had significantly lower CSF darunavir trough concentrations and CSF-to-plasma ratios than patients on darunavir/ritonavir twice-daily (10.7 versus 38.2 ng/ml and 0.32 versus 0.90%; P < 0.05). No significant effect of single-nucleotide polymorphisms in the genes encoding for blood–brain barrier transporters was noted apart from slightly higher CSF darunavir penetration in patients carrying OATP1A2 uncommon variants. Conclusions:This is the first study to compare darunavir CSF concentrations in patients taking the once-daily or the twice-daily dosage: our data show that darunavir and ritonavir dosing significantly affects not only CSF concentrations but also the extent of drug penetration into the CSF. Furthermore a minority of patients in the once-daily arm presented very low CSF concentration of potential concern for HIV control in the central nervous system. The relative importance of pharmacogenetics in influencing CSF darunavir pharmacokinetics deserves further clinical investigation.

Negative Predictive Value of IL28B, SLC28A2, and CYP27B1 SNPs and Low RBV Plasma Exposure for Therapeutic Response to PEG/IFN-RBV Treatment.

Objectives: The response rate to treatment of chronic hepatitis C virus-genotype 1 and 4 infections was recently found to be strongly influenced by many polymorphisms. The aim of our study was to carry out an integrated analysis of the effects of polymorphisms and ribavirin (RBV) plasma exposure on outcome. Methods: The retrospective analysis included 174 patients. IL28B, CYP27B1, SLC29A1, SLC28A3, and SLC28A2 polymorphisms were genotyped and tested for association with sustained virological response. The impact of RBV plasma exposure during the first 3 months of therapy on outcome was also investigated. Results: Considering patients infected by hepatitis C virus-1/4, 3 polymorphisms (IL28B rs8099917TT, CYP27B1 rs4646536TT, and CNT2 rs11854484TT) were associated with sustained virological response. The number of negative variant allele and low RBV exposure were correlated to percentage increasing to therapy failure, suggesting some degree of cumulative effect of the 4 factors. A cutoff of 2.5 &mgr;g/mL of RBV was found to be associated with outcome (area under ROC [AUROC] curve = 0.64, sensitivity = 55.0%, and specificity = 71.2%, P = 0.020). In multivariate logistic regression analyses, each variant allele and RBV plasma exposure cutoff were independently associated with outcome. Conclusions: In this study, we found that additional polymorphisms and RBV plasma exposure are also able to influence the achievement of response. Regardless of the magnitude of RBV pharmacokinetic exposure, the negative predictive value of the polymorphisms here investigated is much stronger than the positive one.

Intracellular accumulation of atazanavir/ritonavir according to plasma concentrations and OATP1B1, ABCB1 and PXR genetic polymorphisms

OBJECTIVES The rate of accumulation of atazanavir and ritonavir within cells is still debated due to methodological limitations. Our aim was to measure peripheral blood mononuclear cell (PBMC) concentrations of atazanavir and ritonavir and investigate whether single-nucleotide polymorphisms of OATP, ABCB1, CYP3A4 and PXR genes are involved in intracellular drug penetration. METHODS HIV-positive patients administered 300 mg of atazanavir/100 mg of ritonavir were enrolled. Blood sampling was performed at the end of the dosing interval (Ctrough). PBMC-associated and plasma atazanavir and ritonavir concentrations were measured by validated HPLC coupled with a single mass detector (HPLC-MS) and HPLC-photodiode array (PDA) methods, respectively. Cell count and mean cellular volume were determined using a Coulter counter. Genotyping was conducted using real-time PCR. RESULTS Thirty-five patients were enrolled. Median atazanavir and ritonavir intracellular concentrations were 1844 and 716 ng/mL, respectively. Median plasma concentrations were 645 ng/mL for atazanavir and 75 ng/mL for ritonavir, while median intracellular/plasma concentration ratios were 2.4 and 9.2, respectively. Median ritonavir intracellular concentrations were higher for OATP1B1 521 T→C TC or CC carriers and for PXR 44477 A→G AG or GG carriers. Atazanavir intracellular/plasma concentration ratios were higher in patients GG for the ABCB1 2677 G→T single-nucleotide polymorphism (SNP) compared with GT and TT groups. CONCLUSIONS Our study showed a higher intracellular ritonavir accumulation than previously reported. Ritonavir intracellular concentrations were associated with OATP1B1 521 and PXR 44477 SNPs while intracellular atazanavir exposure was associated with the ABCB1 2677 SNP. Further clinical studies are necessary in order to confirm these data.

Unexpected drug-drug interaction between tipranavir/ritonavir and enfuvirtide.

Fifty-five patients placed on tipranavir/ritonavir 500/200 mg twice a day (27 with enfuvirtide and 28 without) underwent tipranavir and ritonavir plasma concentration measurements by high-pressure liquid chromatography. Markedly higher tipranavir and ritonavir trough concentrations were observed in enfuvirtide recipients. The modelling of sparse plasma samples using a first order absorption and elimination monocompartmental model without time lag predicted higher tipranavir elimination half-life and volume of distribution in enfuvirtide takers. This unexpected drug–drug interaction warrants further investigation.

Tenofovir Plasma Concentrations According to Companion Drugs: a Cross-Sectional Study of HIV-Positive Patients with Normal Renal Function

ABSTRACT As the risk of tenofovir-associated renal toxicity has been found to be proportional to the drug plasma concentration, our aim was to measure the determinants of tenofovir plasma exposure in HIV-positive patients with normal renal function. A cross-sectional analysis was conducted in HIV-positive patients chronically receiving tenofovir-containing highly active antiretroviral therapies (HAARTs). Patients on tenofovir-containing antiretroviral regimens, presenting 22 to 26 h after drug intake, having estimated glomerular filtration rates above 60 ml/min, reporting high adherence to antiretroviral medications (above 95% of the doses), and signing a written informed consent were included. Plasma tenofovir concentrations were measured through a validated high-performance liquid chromatography–mass spectrometry (HPLC/LC-MS) method. The tenofovir trough concentrations in 195 patients (median, 50 ng/ml, and interquartile range, 35 to 77 ng/ml) were significantly associated with the estimated glomerular filtration rate, body mass index, and third-drug class (protease-containing versus protease-sparing regimens) (with the highest exposure in unboosted-atazanavir recipients). The results of multivariate analysis showed that the third-drug class and the weight/creatinine ratio were independent predictors of tenofovir trough concentrations. This cross-sectional study shows that tenofovir trough concentrations are predicted by the weight/creatinine ratio and by the coadministered antiretrovirals, with protease inhibitors (whether boosted or unboosted) being associated with the highest plasma exposure. These data, previously available in healthy subjects or for some drugs only, could be useful for designing strategies to manage tenofovir-associated toxicity, since this toxicity has been reported to be dose dependent.

Cardiovascular disease in HIV patients: from bench to bedside and backwards

HIV patients are exposed to a higher risk of adverse cardiovascular events, due to complex interactions between traditional risk factors and HIV infection itself in terms of ongoing endothelial dysfunctional immune activation/inflammation and increased risk of thrombosis. On the other hand, long-span antiretroviral therapy administration still raises questions on its long-term safety in an era in which life expectancy is becoming longer and longer while treatment of non-HIV-related serious events is increasingly raising concern. In this article, we will critically analyse the current knowledge of pathological and clinical aspects pertaining to the increased risk of cardiovascular events associated with HIV.

High interpatient variability of raltegravir CSF concentrations in HIV-positive patients: a pharmacogenetic analysis.

OBJECTIVES To analyse the determinants of raltegravir CSF penetration, including the pharmacogenetics of drug transporters located at the blood-brain barrier or blood-CSF barrier. METHODS Plasma and CSF raltegravir concentrations were determined by a validated HPLC coupled with mass spectrometry method in adults on raltegravir-based combination antiretroviral therapy undergoing a lumbar puncture. Single nucleotide polymorphisms in the genes encoding drugs transporters (ABCB1 3435, SLCO1A2, ABCC2 and SLC22A6) and the gene encoding hepatocyte nuclear factor 4 α (HNF4α) were determined by real-time PCR. RESULTS In 41 patients (73.2% male, 95.1% Caucasians), the median raltegravir plasma and CSF concentrations were 165 ng/mL (83-552) and 31 ng/mL (21-56), respectively. CSF-to-plasma ratios (CPRs) ranged from 0.005 to 1.33 (median 0.20, IQR 0.04-0.36). Raltegravir trough CSF concentrations (n = 35) correlated with raltegravir plasma levels (ρ = 0.395, P = 0.019); CPRs were higher in patients with blood-brain barrier damage (0.47 versus 0.18, P = 0.02). HNF4α 613 CG genotype carriers had lower trough CSF concentrations (20 versus 37 ng/mL, P = 0.03) and CPRs (0.12 versus 0.27, P = 0.02). Following multivariate linear regression analysis, the CSF-to-serum albumin ratio was the only independent predictor of raltegravir penetration into the CSF. CONCLUSIONS Raltegravir penetration into the CSF shows a large interpatient variability, although CSF concentrations were above the wild-type IC50 in all patients (and above IC95 in 28.6%). In this cohort, blood-brain barrier permeability is the only independent predictor of raltegravir CPR. The impact of single nucleotide polymorphisms in selected genes on raltegravir penetration warrants further studies.

Intrapatient and interpatient pharmacokinetic variability of raltegravir in the clinical setting.

Introduction Raltegravir (RAL) is the first in class integrase inhibitor and is licensed for administration at 400 mg twice daily. RAL pharmacokinetics are characterized by high interpatient variability and recently RAL plasma exposure has been correlated with efficacy. RAL is primarily metabolized by glucuronidation via uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) and UGT1A1*28 considered to be the main genetic variant associated with decreased UGT1A1 expression. This study investigated variability in RAL trough plasma concentrations (Ctrough) in the clinical setting, the effect of UGT1A1*28 and concomitant antiretrovirals. Methods A total of 86 patients, from Turin, Italy, and Madrid, Spain, were included in the analysis. Blood samples were obtained 10–14 hours postdose. Genotyping for UGT1A1*28 was conducted by sequencing. Results High interpatient and intrapatient variabilities were observed; 13 patients had ≥3 samples available, and the median coefficient of variation was 128 (64–265). Coadministration of RAL with atazanavir (ATV, n = 9) resulted in higher raltegravir Ctrough, 517 (307–2706) ng/mL when compared with patients not receiving ATV (n = 77) 223 (95–552; P = 0.02). UGT1A1*28 did not influence RAL plasma exposure. Discussion We have documented large intersubject and intrasubject variabilities in RAL plasma concentrations and confirmed the interaction with ATV. Further studies are required to better understand the mechanisms that influence the pharmacokinetics of RAL.