Pharmacogenetics of the anti-HCV drug sofosbuvir: a preliminary study.

Background: Sofosbuvir is a potent nucleotide HCV NS5B polymerase inhibitor that is also a P-glycoprotein (encoded by the ABCB1 gene) and breast cancer resistance protein (encoded by the ABCG2 gene) substrate. Concerning previous anti-HCV therapies, pharmacogenetics had a significant impact, particularly considering the association of interleukin28B polymorphisms with dual-therapy (ribavirin + pegylated IFN) outcomes. Objectives: In this work, we investigated the association between sofosbuvir and its prevalent metabolite (GS-331007) plasma concentrations at 1 month of therapy and genetic variants (SNPs) in genes encoding transporters and nuclear factors (ABCB1, ABCG2 and HNF4α) related to sofosbuvir transport. Patients and methods: Allelic discrimination was performed through real-time PCR, whereas plasma concentrations were evaluated through liquid chromatography. One hundred and thirteen patients were enrolled. Results: Sofosbuvir concentrations were below the limit of quantification since the drug was converted into its GS-331007 metabolite. ABCB1 2677 G>T (P = 0.044) and HNF4α 975 C>G (P = 0.049) SNPs were associated with GS-331007 metabolite plasma concentrations. In linear multivariate analysis, liver stiffness, insulin resistance, baseline haemoglobin and haematocrit and SNPs in the ABCB1 gene (3435 CT/TT and 1236 TT genotypes) were significant predictors of GS-331007 concentrations. Furthermore, we performed sub-analyses considering the anti-HCV concomitant drug and HCV genotype, identifying specific polymorphisms associated with GS-331007 plasma concentrations: ABCB1 3435 C>T and HNF4α975 C>G in patients treated with daclatasvir, ABCB1 2677 G>T with ledipasvir and ABCB1 3435 C>T, ABCB1 2677 G>T, ABCG2 421 C>A and ABCG2 1194 + 928 C>A with ribavirin. Conclusions: In this study we suggested sofosbuvir GS-331007 metabolite plasma levels were affected by variants in the ABCB1 and HNFα genes.

Therapeutic drug monitoring of voriconazole for treatment and prophylaxis of invasive fungal infection in children.

Voriconazole therapeutic drug monitoring is not consistently recommended due to its high interpatient and intrapatient variability. Here, we aimed to describe our experience with voriconazole for treatment and prophylaxis of invasive fungal infections in paediatric patients. A fully validated high-performance liquid chromatography-mass spectrometry method was used to quantify voriconazole concentration in plasma, at the end of dosing interval. A high interindividual variability was shown. We enrolled 237 children, 83 receiving intravenous and 154 oral voriconazole. A positive correlation between drug dose and drug plasma exposure was observed. Considering intravenous route, patients with higher serum creatinine had higher voriconazole concentrations; a positive correlation was found among drug exposure and age. Sex significantly influenced drug levels: males had higher median drug concentrations than females (P < 0.001). Close voriconazole pharmacokinetics monitoring should help individualize antifungal therapy for children.

Influence of ABCB11 and HNF4α genes on daclatasvir plasma concentration: preliminary pharmacogenetic data from the Kineti-C study.

Background: Daclatasvir is an inhibitor of HCV non-structural 5A protein and is a P-glycoprotein substrate. Pharmacogenetics has had a great impact on previous anti-HCV therapies, particularly considering the association of IL-28B polymorphisms with dual therapy outcome. Objectives: We investigated the association between daclatasvir plasma concentrations at 2 weeks and 1 month of therapy and genetic variants (SNPs) in genes encoding transporters and nuclear factors (ABCB1, ABCB11 and HNF4α). Patients and methods: Allelic discrimination was achieved through real-time PCR, whereas plasma concentrations were evaluated through LC-MS/MS. Results: Fifty-two patients were analysed, all enrolled in the Kineti-C study. HNF4α 975 C > G polymorphism was found to be associated with the daclatasvir plasma concentrations at 2 weeks (P = 0.009) and 1 month of therapy (P = 0.006). Linear regression analysis suggested that, at 2 weeks of therapy, age, baseline BMI and haematocrit were significant predictors of daclatasvir concentrations, whereas at 1 month of therapy ABCB111131 CC and HNF4α CG/GG genotypes were significant predictors of daclatasvir concentrations. Conclusions: These are the first and preliminary results from our clinical study focusing on daclatasvir pharmacogenetics, showing that this approach could have a role in the era of new anti-HCV therapies.

Treatment with daclatasvir and sofosbuvir for 24 weeks without ribavirin in cirrhotic patients who failed first-generation protease inhibitors.

BACKGROUND: Treatment of patients with chronic hepatitis C who failed the triple therapy with first generation of protease inhibitors is not still defined. The combined use of sofosbuvir (SOF) and daclatasvir (DCV) seems to be promising due to higher genetic barrier, good tolerance and effectiveness. METHODS: We described the treatment with this drug combination in a real-life cohort of 20 cirrhotic patients with genotype 1 who failed the triple therapy. RESULTS: 18 of them (90%) with Child-Pugh A, 11 (55%) with genotype 1a, 17 (85%) with more than 1 and 8 (40%) with more than 2 previous failed treatment; all patients had at baseline NS3 resistance-associated variants related to triple therapy failure. RBV was not administered due to anemia in previous treatments. The sustained virological response was 100%. CONCLUSION: Treatment with SOF + DCV without RBV for 24 weeks is safe and effective in cirrhotic patients who failed triple therapy with the first generation of protease inhibitors.

Pharmacokinetic evaluation of oral itraconazole for antifungal prophylaxis in children.

Itraconazole is a first-generation triazole agent with an extended spectrum of activity; it is licensed in adults for superficial and systemic fungal infections; no recommendation has been yet established for use in children patients. Its variable and unpredictable oral bioavailability make it difficult to determine the optimal dosing regimen. Hence, therapeutic drug monitoring, highly available in clinical practice, may improve itraconazole treatment success and safety. The aim of the study was to describe in paediatrics the oral itraconazole pharmacokinetics, used for prophylaxis. Moreover, we evaluated the utility of its therapeutic drug monitoring in this cohort. A fully validated chromatographic method was used to quantify itraconazole concentration in plasma collected from paediatric patients, at the end of dosing interval. Associations between variables were tested using the Pearson test. Mann-Whitney U test has been used to probe the influence of categorical variables on continuous ones. Any predictive power of the considered variables was finally evaluated through univariate and multivariate linear and logistic regression analyses. A high inter-individual variability was shown; ethnicity (beta coefficient, ß -0.161 and interval of confidence at 95%, IC -395.035; -62.383) and gender (ß 0.123 and IC 9.590; 349.395) remained in the final linear regression model with P value of .007 and .038, respectively. This study highlights that therapeutic drug monitoring is required to achieve an adequate target itraconazole serum exposure.

Vitamin D pathway gene polymorphisms as predictors of hepatitis C virus-related mixed cryoglobulinemia.

Mixed cryoglobulinemia (MC) is the most frequent extrahepatic hepatitis C virus (HCV) complication. Vitamin D is a modulator of several biological processes, including immune and skeletal systems and MC presence and systemic vasculitis were associated independently with low levels of vitamin D. Considering the impact of vitamin D, we aimed to evaluate the role of some single nucleotide polymorphisms (SNPs) of vitamin D pathway genes in the prediction of MC in HCV patients treated with pegylated interferon and ribavirin. We investigated SNPs in IL-28B, CYP27B1, CYP27A1, CYP24A1, VDBP, and VDR genes through real-time PCR. VDR gene SNPs were related to baseline viral load: VDR BsmI AA (P=0.018), TaqI CC (P=0.009), and ApaI AA (P=0.004) showed a lower baseline HCV count. Among vitamin D pathway gene polymorphisms, VDR FokI T>C was a factor associated with the presence of MC in the study population (P=0.011): related to C allele carriers (TT vs. TC/CC), we obtained a P-value of 0.003. In the logistic regression analysis to assess which demographic, clinical, or genetic factors could predict the presence of cryoglobulin, the TT/CC IL-28B rs8099917/rs12979860 haplotype [P<0.001; odds ratio (OR) 3.516 (1.951-6.336)], baseline viral load [P<0.001; OR 1.000 (0.999-1.001)], and VDR FokI TC/CC genotypes [0.044; OR 0.463 (0.218-0.981)] remained in the final regression model. These data could help physicians identify patients with a higher probability of developing MC extrahepatic complications.

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.

Vitamin D pathway genetic variants are able to influence sofosbuvir and its main metabolite pharmacokinetics in HCV mono-infected patients.

Vitamin D levels and genetic variants were associated with drug outcome/toxicity and concentrations. The plasma exposure of GS-331007, the main sofosbuvir metabolite, has been related to SVR. We evaluated the impact of polymorphisms in genes (CYP27B1, CYP24A1, VDBP and VDR) related to vitamin D pathway on sofosbuvir and GS-331007 plasma levels in HCV mono-infected patients at one month of treatment. Polymorphisms were investigated through real-time PCR; drug plasma quantification was performed through a UHPLC-MS/MS method. GS-331007 levels were associated with CYP24A1rs2248359 and VDRCdx2 variants in all the analyzed patients and linear regression analysis showed that sex, body mass index, HCV genotype, baseline estimated glomerular filtration rate, VDRCdx2AG/GG and CYP27B1-1260TT genotypes significantly predict concentrations. We performed sub-analyses considering the HCV genotype and the concomitant drug, identifying polymorphisms associated with GS-331007 concentrations. This is the first study focusing on vitamin D pathway gene variants and DAAs concentrations, but further studies are required.

Vitamin D pathway gene polymorphisms and hepatocellular carcinoma in chronic hepatitis C-affected patients treated with new drugs.

PURPOSE: Since HCV infection may lead to hepatocellular carcinoma (HCC) and vitamin D (deficiency) is related to cancer, we investigated if SNPs in genes involved in vitamin D pathway could predict HCV-related HCC presence in patients treated with new anti-HCV drugs. METHODS: Patients with chronic hepatitis C and treated with direct-acting antivirals were enrolled. SNPs in VDR, CYP27B1, CYP24A1 and GC genes were assessed through real-time PCR. 258 patients were analyzed. RESULTS: HCC was present in six patients, all taking sofosbuvir, all males and five/six had cirrhosis. HCV-RNA log levels at baseline were statistically different between patients with and without HCC. VDR FokI T > C SNP resulted associated with HCC: all the CC patients were free from HCC. An association between HCC presence and undetectable HCV-RNA at 1 month of therapy was suggested; cirrhosis was related to HCC. HCC risk factors were age, ribavirin administration, IL28Brs12979860CC and previous treatments; VDR FokICC, sex and insulin resistance were protective factors. CONCLUSIONS: These data highlighted vitamin D pathway gene SNPs and HCC relationship in the Italian population; further studies are required.

Cannabinoids concentration variability in cannabis olive oil galenic preparations.

OBJECTIVES: Knowledge of the exact concentration of active compounds in galenic preparations is crucial to be able to ensure their quality and to properly administer the prescribed dose. Currently, the need for titration of extracts is still debated. Considering this, together with the absence of a standard preparation method, the aim of this study was to evaluate cannabinoids concentrations variability in galenic olive oil extracts, to evaluate the interlot and interlaboratory variability in the extraction yield and in the preparation composition. METHODS: Two hundred and one extracts (123 (61.2%) from Bedrocan® , 54 (26.9%) from Bediol® , 11 (5.5%) from Bedrolite® , and 13 (6.5%) from mixed preparations) were analysed by liquid chromatography coupled with tandem mass spectrometry, quantifying cannabinoids (THC, CBD, THCA, CBDA and CBN) concentrations. KEY FINDINGS: The RSD% of THC and CBD concentrations resulted higher than 50%. Specifically for Bedrocan® , Bediol® , Bedrolite® (5 g/50 ml), these were THC 82%, THC 53% and CBD 91%, THC 58% and CBD 59%, respectively. The median extraction yields were greater than 75% for all preparations. CONCLUSIONS: Our results highlighted a wide variability in THC and CBD concentrations that justify the need for titration and opens further questions about other pharmaceutical preparations without regulatory indication for this procedure.

Vitamin D pathway gene polymorphisms affecting daclatasvir plasma concentration at 2 weeks and 1 month of therapy.

AIM: Vitamin D (VD) influences genetic expression through its receptor (VDR). VD pathway gene polymorphisms seem to influence antiviral drug pharmacokinetics and therapeutic outcome/toxicity. We investigated the association between daclatasvir (DCV) plasma concentrations and genetic variants (SNPs) associated with the VD pathway. PATIENTS & METHODS: Chronic hepatitis C patients treated with DCV from 2014 to 2016 were included. Genotypes were assessed through real-time PCR and plasma concentrations through liquid chromatography. RESULTS: A total of 52 patients were analyzed. DCV levels were influenced by CYP24A1 rs2248359T>C polymorphism at 2 weeks and VDR Cdx2 A>G at 1 month of treatment. Linear regression analysis showed baseline BMI, alanine aminotransferase and hematocrit as significant predictors of DCV concentrations at 2 weeks, BMI and hematocrit at baseline, VDR Cdx2 AG/GG and FokI TC/CC at 1 month. CONCLUSION: These results showed a possible role of VD pathway gene polymorphisms in influencing DCV plasma concentrations, but further studies are required.

Pharmacogenetic of voriconazole antifungal agent in pediatric patients.

AIM: We explored the role of SNPs within the SLCO1B3, SLCO1B1, SLC22A6, ABCB1, ABCG2, SLCO3A1, CYP2C19, ABCC2, SLC22A1, ABCB11 and NR1I2 genes on voriconazole pharmacokinetics. PATIENTS & METHODS: 233 pediatric patients were enrolled. Drug plasma Ctrough was measured by a HPLC-MS method. Allelic discrimination was performed by qualitative real-time PCR. RESULTS: SLCO1B3 rs4149117 c.334 GT/TT (p = 0.046), ABCG2 rs13120400 c.1194 + 928 CC (p = 0.029) and ABCC2 rs717620 c.-24 GA/AA (p = 0.025) genotype groups significantly influenced Ctrough. ethnicity (p = 0.042), sex (p = 0.033), SLCO1B3 rs4149117 c.334 GT/TT (p = 0.041) and ABCB1 rs1045642 c.3435 TT (p = 0.016) have been retained in linear regression model as voriconazole predictor factors. CONCLUSION: Understanding how some gene polymorphisms affect the voriconazole pharmacokinetic is essential to optimally dose this agent.

Role of simeprevir plasma concentrations in HCV treated patients with dermatological manifestations.

BACKGROUND AND AIMS: Up till now the role of simeprevir plasma concentrations has not been described in treated patients affected by chronic hepatitis C and with dermatological side-effects. In this study, we have evaluated a possible relationship between plasma levels and the onset of skin complaints for the first time. METHODS: We report a clinical and pharmacokinetic analysis of 56 patients treated with simeprevir-based therapies. RESULTS: Simeprevir plasma concentrations were significantly related to dermatological side-effects at early time-points (P<0.001). In logistic regression, simeprevir concentrations at 1 week was the best predictive factor forskin symptoms (OR=1.901, 95%IC: 1.001-2.304; P=0.007). CONCLUSION: Simeprevir plasma measurements could be a useful tool in a real-life clinical setting for prevention of dermatological symptoms.

Association of vitamin D pathway SNPs and clinical response to interferon in a cohort of HBeAg-negative patients.

AIM: Vitamin D modulates biological processes; an influence of vitamin D levels and genetic variants was identified concerning hepatitis B virus infection. We evaluated the role of some SNPs of vitamin D pathway genes in some clinical features of hepatitis B affected patients treated with pegylated interferon. METHODS: We investigated SNPs in IL-28B, CYP27B1, CYP27A1, CYP24A1, VDBP and VDR genes, through real-time PCR. RESULTS:  VDRApaI SNP was associated to viral load and HBsAg presence at different timings. In logistic regression analyses, VDRApaI AA genotype predicted baseline viral load >6 Log IU/ml (marker of nonresponse), and both virological and biochemical responses. CONCLUSION: Pharmacogenetic data could help physicians in the prediction of patients with higher probability to achieve a good response.

Pharmacogenetic analysis of hepatitis C virus related mixed cryoglobulinemia.

AIM: Mixed cryoglobulinemia (MC) is an extra hepatic hepatitis C virus related problem and different studies suggested genetics' role in predicting this complication. We evaluated the influence of SNPs in IL-28B, SLC29A1, SLC28A2, NT5C2, HNF4 and ABCB1 genes in MC prediction. PATIENTS & METHODS: SNPs were evaluated through real-time PCR. RESULTS:  ABCB1 (gene encoding P-glycoprotein) 3435C>T SNP was associated with MC presence (p = 0.034): related to T allele carriers (CC vs CT/TT), we reached a p-value of 0.013. In the logistic regression analysis baseline viral load >600.000 IU/ml (p < 001), IL28B rs8099917/rs12979860 TT/CC (p < 0.001), NT5 (gene encoding for 5' nucleotidase) 153 TC (p = 0.012) and ABCB1 3435 CT/TT (p = 0.034) genotypes predicted MC presence. CONCLUSION: These data could help clinicians to identify patients with higher probability to show MC extra hepatic complication.

Evaluation of Posaconazole Pharmacokinetics in Adult Patients with Invasive Fungal Infection.

Mortality and morbidity due to invasive fungal infections have increased over the years. Posaconazole is a second-generation triazole agent with an extended spectrum of activity, which shows a high interindividual variability in its plasma levels, rendering dosing in many patients inconsistent or inadequate. Hence, posaconazole therapeutic drug monitoring, which is easily available in clinical practice, may improve treatment success and safety. The aim of the study was to describe posaconazole pharmacokinetics, and to evaluate the utility of therapeutic drug monitoring for therapy and prophylaxis in a cohort of adult patients. A fully validated chromatographic method was used to quantify posaconazole concentration in plasma collected from adult patients at the end of the dosing interval. Associations between variables were tested using the Pearson test. The Mann-Whitney test was used to probe the influence of categorical variables on continuous ones. A high inter-individual variability was shown. Of the 172 enrolled patients, among those receiving the drug by the oral route (N = 170), gender significantly influenced drug exposure: males showed greater posaconazole concentration than females (p = 0.028). This study highlights the importance of therapeutic drug monitoring in those with invasive fungal infections and its significant clinical implications; moreover we propose, for the first time, the possible influence of gender on posaconazole exposure.

UPLC-MS/MS method for the simultaneous quantification of three new antiretroviral drugs, dolutegravir, elvitegravir and rilpivirine, and other thirteen antiretroviral agents plus cobicistat and ritonavir boosters in human plasma.

Rilpivirine (RPV), dolutegravir (DTG) and elvitegravir (EVG) are the latest antiretroviral drugs approved for treatment of HIV infection. Currently, poor information is currently available concerning their pharmacokinetic and pharmacodynamic properties, thus making the use of therapeutic drug monitoring for these drugs not useful. This lack of information is partially due to the absence of an high-throughput method for their simultaneous quantification together with other antiretroviral drugs. In this work, we describe the development and validation of a new UPLC-MS/MS method to quantify these drugs, together with other fourteen antiretroviral agents, in human plasma. One hundred microliters of plasma samples were added with internal standard (6,7-Dimethyl- 2,3-di(2-pyridyl) quinoxaline), underwent a simple protein precipitation with methanol:acetonitrile (50:50v/v) followed by sample dilution with water. Chromatographic separation was performed on a Acquity® UPLC HSS T3 column (150mm x 2.1mm I.D) with a particle size of 1.8µm and compounds were detected with a tandem mass detector, monitoring two ion transitions for each drugs. The mean recovery of RPV, DTG and EVG were 101%, 87% and 112.3% respectively. Accuracy and precision inter/intra-day were below 15% for all drugs, in accordance to Food and Drug Administration guidelines requirements. The UPLC-MS/MS method reported here could be used routinely to monitor plasma concentrations of antiviral drugs, including RPV, DTG and EVG.

A UHPLC-MS/MS method for the quantification of direct antiviral agents simeprevir, daclatasvir, ledipasvir, sofosbuvir/GS-331007, dasabuvir, ombitasvir and paritaprevir, together with ritonavir, in human plasma.

To date, the new standard for treatment of chronic hepatitis C is based on the administration of novel direct acting antivirals. Among these, sofosbuvir, simeprevir, daclatasvir, ledipasvir, dasabuvir, ombitasvir and paritaprevir already entered the clinical use. Anyway, since few pharmacokinetic studies have been conducted on these drugs in a "real life" context poor knowledge is available about their optimal therapeutic range. Without this background, therapeutic drug monitoring is not applicable for treatment optimization. Up to now, a few methods are reported to quantify these drugs in human plasma, and none of them in a simultaneous way. The aim of this work was to develop and validate a simple, fast and cheap, but still reliable UHPLC-MS/MS method for the quantification of these drugs, feasible for a clinical routine use. Solid phase extraction was performed using HLB C18 96-well plates. Chromatographic separation was performed on a BEH C18 1.7µm, 2.1mm×50mm column, settled at 50°C, with a gradient run of two mobile phases: ammonium acetate 5mM (pH 9.5) and acetonitrile, with a flow rate of 0.4mL/min for 5min. Tandem-mass detection was carried out in positive electrospray ionization mode. Both inter and intraday imprecision and inaccuracy were below 15%, as required by FDA guidelines, while both recoveries and matrix effects resulted within the acceptance criteria. The method was tested on 80 patients samples with good performance. Being robust, simple and fast and requiring a low plasma volume, this method resulted eligible for a clinical routine use.

A LC-MS method to quantify tenofovir urinary concentrations in treated patients.

Tenofovir disoproxil fumarate is a prodrug of tenofovir used in the treatment of HIV and HBV infections: it is the most used antiretroviral worldwide. Tenofovir is nucleotidic HIV reverse trascriptase inhibitor that showed excellent long-term efficacy and tolerability. However renal and bone complications (proximal tubulopathy, hypophosphatemia, decreased bone mineral density, and reduced creatinine clearance) limit its use. Tenofovir renal toxicity has been suggested as the consequence of drug entrapment in proximal tubular cells: measuring tenofovir urinary concentrations may be a proxy of this event and it may be used as predictor of tenofovir side effects. No method is currently available for quantifying tenofovir in this matrix: then, the aim of this work was to validate a new LC-MS method for the quantification of urinary tenofovir. Chromatographic separation was achieved with a gradient (acetonitrile and water with formic acid 0.05%) on an Atlantis 5 µm T3, 4.6 mm × 150 mm, reversed phase analytical column. Detection of tenofovir and internal standard was achieved by electrospray ionization mass spectrometry in the positive ion mode. Calibration ranged from 391 to 100,000 ng/mL. The limit of quantification was 391 ng/mL and the limit of detection was 195 ng/mL. Mean recovery of tenofovir and internal standard were consistent and stable, while matrix effect resulted low and stable. The method was tested on 35 urine samples from HIV-positive patients treated with tenofovir-based HAARTs and did not show any significant interference with antiretrovirals or other concomitantly administered drugs. All the observed concentrations in real samples fitted the calibration range, confirming the capability of this method for the use in clinical routine. Whether confirmed in ad hoc studies this method may be used for quantifying tenofovir urinary concentrations and help managing HIV-positive patients treated with tenofovir.