A UPLC-MS-MS method for the simultaneous quantification of first-line antituberculars in plasma and in PBMCs.

OBJECTIVES: TB is currently the second cause of death among patients affected with infectious diseases. Quantification of drug levels in plasma and in cells where Mycobacterium tuberculosis persists and grows may be useful in understanding the appropriateness of dosage regimens. We report a new and fully validated chromatographic method to quantify first-line antituberculars in plasma and PBMCs. The method was used for plasma and cell quantification of antituberculars in patients undergoing treatment with standard oral therapy. METHODS: Ethambutol, isoniazid, pyrazinamide and rifampicin were extracted from plasma and PBMCs using two separate and optimized procedures; analysis was performed using UPLC coupled with a mass-mass detector system (UPLC-MS-MS). Antitubercular levels in patients were assayed at the end of the dosing interval (C trough) and 2 h post-dose (C max). RESULTS: The method was accurate and precise. Recovery and the matrix effect were reproducible. While rifampicin intracellular concentrations were similar to plasma values (median intra-PBMC C max = 7503 ng/mL versus median plasma C max = 6505 ng/mL), isoniazid and pyrazinamide intracellular concentrations were lower than plasma values (median intra-PBMC C max = 12 ng/mL versus median plasma C max = 3258 ng/mL for isoniazid and median intra-PBMC C max = 2364 ng/mL versus median plasma C max = 26 988 ng/mL for pyrazinamide) and ethambutol intracellular concentrations were significantly higher than plasma values (median intra-PBMC C max = 73 334 ng/mL versus median plasma C max = 2244 ng/mL). CONCLUSIONS: The method was suitable for both therapeutic drug monitoring and for pharmacokinetic analysis. Should the clinical usefulness of measuring antitubercular drug intracellular concentrations be confirmed, this method could be useful to enhance the clinical application of intra-PBMC evaluation.

Development and validation of a HPLC-UV method for the quantification of antiepileptic drugs in dried plasma spots.

BACKGROUND: Therapeutic drug monitoring (TDM) of antiepileptic drugs is widely used in clinical practice to optimise therapy, but it is limited by technical problems and cost considerations. The aim of the present study was: 1) to validate a chromatographic method for the concomitant determination of levetiracetam, lamotrigine, ethosuximide, felbamate, rufinamide, zonisamide and monohydroxycarbamazepine; 2) to develop it for dried plasma spot (DPS) assessing its reliability against the classical determination from plasma; and 3) test its clinical application. METHODS: Extraction of plasma samples and DPS was done by simple precipitation. Chromatographic analysis was performed using high performance liquid chromatography with ultraviolet detection. After validation, both methods were applied for the quantification of plasma samples from patients on antiepileptic therapy. RESULTS: Mean inter- and intra-day accuracy and precision were <15% for all compounds both in plasma and in DPS samples. DPS samples were considered stable under tested conditions. Measurements between plasma and DPS samples appeared related (p<0.0001). Bland-Altman analysis revealed accordance in lamotrigine values with mean overestimation of concentration for DPS sample of 2.8%. Also for monohydroxycarbamazepine data the agreement was acceptable (mean overestimation of 9.2%). For levetiracetam mean difference was 7.6%, while for ethosuximide mean percentage difference was 20.6%. CONCLUSIONS: The developed methods simplify TDM of antiepileptic drugs. This is particularly relevant for the method on dried spot sample devices because it facilitates further sample handling, stability and shipments making the management of therapies in epileptic patients easier also in hospitals devoid of a dedicated laboratory.

Intracellular accumulation of ritonavir combined with different protease inhibitors and correlations between concentrations in plasma and peripheral blood mononuclear cells.

OBJECTIVES: Ritonavir, used at low doses as a boosting agent of other protease inhibitors (PIs), is known to be associated with metabolic complications and gastrointestinal disturbances. The rate of accumulation of ritonavir within cells is still debated due to scarce data and methodological limitations. Therefore, our aim was to evaluate intracellular ritonavir penetration when used with different boosted PIs in the clinical setting. METHODS: Patients administered with atazanavir/ritonavir (300/100 mg, once daily), darunavir/ritonavir [600/100 mg, twice daily (darunavir-600) and 800/100 mg, once daily (darunavir-800)], lopinavir/ritonavir (400/100 mg, twice daily) and tipranavir/ritonavir (500/200 mg, twice daily) were considered. Blood sampling at the end of the dosing interval (Ctrough) was performed. Peripheral blood mononuclear cell (PBMC)-associated and plasma ritonavir and PI concentrations were measured by validated HPLC methods. PBMC count and individual mean cell volume (MCV) were measured using a Coulter Counter instrument. RESULTS: One hundred patients were enrolled. Frequencies of ritonavir-boosted PIs were atazanavir, 37%; darunavir-600, 23%; lopinavir, 19%; tipranavir, 13%; and darunavir-800, 8%. The median intracellular and plasma concentrations of ritonavir were 1279 ng/mL (IQR 727-2087) and 170 ng/mL (IQR 82-384), respectively, accounting for a cellular accumulation ratio of 7.69 (5.7-10.9). Significant differences in ritonavir intracellular concentrations emerged among different PIs (P<0.001): specifically between darunavir-600 and atazanavir (P<0.001), between darunavir-600 and tipranavir (P=0.009), between atazanavir and lopinavir (P<0.001) and between lopinavir and tipranavir (P=0.027). CONCLUSIONS: Our study showed a higher rate of ritonavir intracellular accumulation than previously reported, possibly due to the more accurate calculation of intracellular concentrations by MCV. The ratio varied according to concomitantly administered PIs, suggesting their influence on the rate of ritonavir intracellular penetration.

Kinetics and prediction of HBsAg loss during therapy with analogues in patients affected by chronic hepatitis B HBeAg negative and genotype D.

BACKGROUND & AIMS: In patients affected by chronic hepatitis because of HBV infection, long-term suppressive therapy with nucleos(t)ides analogues in the HBeAg- patients has shown low effects on HBsAg titre (qHBsAg) decrease, and HBsAg loss is difficult to achieve. Thus, in this type of patients the main goals of antiviral therapy is the suppression of HBV-DNA and ALT normalization. METHODS: We retrospectively evaluated different qHBsAg kinetics in 134 treatment-naïve patients having the same characteristics: HBeAg-, infection sustained by HBV genotype D and persistently undetectable HBV-DNA. Patients were treated with NAs therapy (lamivudine, adefovir, telbivudine, entecavir and tenofovir) for at least 2 years. qHBsAg was performed every 6 months. RESULTS: Our results showed a significantly greater qHBsAg decline after 2 years in patients treated with tenofovir (0.45 logIU/ml) than in patients treated with telbivudine (0.12 logIU/ml; P < 0.001). The calculated expected time to HBsAg loss was shorter in the tenofovir group than in the telbivudine group (nearly 17 vs 63 years, P < 0.001). CONCLUSIONS: HBeAg negative patients infected by HBV genotype D should be treated with more potent NAs such as entecavir or tenofovir to obtain a significant qHBsAg decrease, but the achievement of HBsAg loss seems to require almost two decades of therapy.

Ultra performance liquid chromatography PDA method for determination of tigecycline in human plasma.

: A simple ultra performance liquid chromatography with photodiode array method for the quantification of human plasma concentrations of tigecycline was developed and validated. Quinaxoline, used as an internal standard, was added to 500 µL of plasma before adding 1 mL of protein precipitation solution. The extracts were dried in a vacuum centrifuge system at 60°C and reconstituted with 60 µL of water and acetonitrile (95:5, vol/vol), and 5 µL was injected onto an ACQUITY UPLC H-Class system. Chromatographic separation was performed on a C18 ACQUITY UPLC HSS T3 column using a gradient of potassium phosphate buffer (pH 3.2) and acetonitrile. Detection was performed using a photodiode array detector at 350 nm. Relative error at 3 quality control concentrations ranged from -2.49% to -8.74%. Intraday and interday (percent relative standard error) precision ranged from 3.93% to 12.27% and from 9.53% to 13.32%, respectively. Limit of quantification and limit of detection were 0.024 and 0.006 µg/mL, respectively. Mean recovery was 95%. The calibration curve was linear up to 6 µg/mL. This concentration range proved to be adequate to measure tigecycline concentrations in patients treated with the drug, therefore this method would be suitable for therapeutic drug monitoring.

Pharmacokinetics of caspofungin increased dosage in a patient on rifampin-containing anti-tubercular treatment.

We describe a patient treated with caspofungin and rifampin; after increasing the dosage of the former (70 mg/day) we observed an unexpectedly lower plasma exposure (AUC0-24 79.5 µg/ml*h vs. 108.8 µg/ml*h). Although rifampin-mediated complete enzyme induction may take longer than 2 weeks, the clinical advantage of an increased caspofungin dose deserves clinical investigation.

Development and validation of a new method to simultaneously quantify triazoles in plasma spotted on dry sample spot devices and analysed by HPLC-MS.

OBJECTIVES: Therapeutic drug monitoring (TDM) of triazoles is widely used in clinical practice to optimize therapy. TDM is limited by technical problems and cost considerations, such as sample storage and dry-ice shipping. We aimed to develop and validate a new method to analyse itraconazole, posaconazole and voriconazole in plasma spotted on dry sample spot devices (DSSDs) and to quantify them by an HPLC system. METHODS: Extraction from DSSDs was done using n-hexane/ethyl acetate and ammonia solution. Samples were analysed using HPLC with mass spectrometry (HPLC-MS). Accuracy and precision were assayed by inter- and intra-day validation. The stability of triazoles in plasma spotted on DSSDs was investigated at room temperature for 1 month. The method was compared with a validated standard HPLC method for quantification of triazoles in human plasma. RESULTS: Mean inter- and intra-day accuracy and precision were <15% for all compounds. Triazoles were stable for 2 weeks at room temperature. The method was linear (r(2) > 0.999) in the range 0.031-8 mg/L for itraconazole and posaconazole, and 0.058-15 mg/L for voriconazole. High sensitivity was observed; limits of detection were 0.008, 0.004 and 0.007 mg/L for itraconazole, posaconazole and voriconazole, respectively. A high degree of correlation (r(2) > 0.94) was obtained between the DSSD method and the standard method of analysis. CONCLUSIONS: The method that we developed and validated to quantify triazoles in human plasma spotted on DSSDs is accurate and precise. It overcomes problems related to plasma sample storage and shipment, allowing TDM to be performed in a cheaper and safer manner.

Influence of CYP2B6 and ABCB1 SNPs on nevirapine plasma concentrations in Burundese HIV-positive patients using dried sample spot devices.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: • Nevirapine pharmacokinetics are affected by several factors including CYP2B6 single nucleotide polymorphisms (SNPs). These genetic profiles are more common in African patients and they affect the drug clearance being associated with higher trough concentrations. Pharmacokinetic/pharmacogenetic (PK/PG) studies are difficult to perform in remote areas where refrigeration is not available, although dried plasma and dried blood methods have been validated. WHAT THIS STUDY ADDS: • Dried plasma spots are useful tools for studying nevirapine PK with a good association to plasma concentrations and they can be used in rural areas since a cold chain is not necessary. Dried blood spots can be used to store and analyze patients' DNA for PG polymorphisms. Nevirapine trough concentrations in Burundese patients, not studied so far, are above the target concentration (3000 ng ml(-1) ) in 84% of patients. CYP2B6 (both at position 516 and 983) but not ABCB1 (3435 and 1236) SNPs as well as age correlate with higher nevirapine exposure. AIMS: The pharmacokinetics (PK) and pharmacogenetics (PG) of nevirapine have been studied in rich and limited-resource countries. CYP2B6 single nucleotide polymorphisms (SNPs) have been associated with decreased drug clearance. We evaluated the PG determinants of nevirapine trough concentrations in a rural cohort in Burundi using easy to store and transport dried sample spot devices. METHODS: A cross-sectional analysis in HIV-positive nevirapine-treated patients in Kiremba, north of Burundi, was performed in 2009. After blood withdrawal whole blood was stored on dried blood spots and plasma (after centrifugation) was placed on dried plasma spot devices and stored at room temperature. Nevirapine plasma and dried sample spot concentrations were compared to test the clinical usefulness of this method. SNPs in CYP2B6 and ABCB1 (using a real time PCR technique) were analyzed and associated with nevirapine plasma trough concentrations. RESULTS: Nevirapine concentrations measured on dried plasma spot devices were highly related to plasma concentrations in 60 patients, although a negative bias was observed (-18%). Nevirapine trough concentrations were above the target concentration (3000 ng ml(-1) ) in 84% of patients and they were associated with CYP2B6 SNPs (both at position 516 and 983). No effect of ABCB1 SNPs was noted. CONCLUSIONS: Dried plasma spot devices are accurate tools for measuring nevirapine concentrations in rural settings where refrigeration is not available, despite a moderate underestimation bias. They allowed the evaluation of nevirapine concentrations in a cohort of HIV-infected people in rural Burundi, confirming very good exposure and correlation with PG polymorphisms in the CYP2B6 encoding gene.

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.

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 µg/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.

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 χ 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). RBV concentrations were not influenced by ITPA genotypes. A cut-off of 2.3 µg/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 µg/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.

Evaluation of the mean corpuscular volume of peripheral blood mononuclear cells of HIV patients by a coulter counter to determine intracellular drug concentrations.

The mean corpuscular volume (MCV) of peripheral blood mononuclear cells (PBMCs) was determined by Coulter Counter, and data were used to calculate the intracellular drug concentrations. A total of 574 PBMC samples were collected from 190 patients. The MCV was 282.9 fl (minimum, 207.0; maximum, 354.6), with a standard deviation of 8.8%. Previous reports have often used a fixed value of 400 fl for the MCV, which may result in artificially low estimates of the intracellular concentrations of antivirals.

Comparative evaluation of seven resistance interpretation algorithms and their derived genotypic inhibitory quotients for the prediction of 48 week virological response to darunavir-based salvage regimens.

BACKGROUND: the darunavir genotypic inhibitory quotient (gIQ) has been suggested as one of the predictors of virological response to darunavir-containing salvage regimens. Nevertheless, which resistance algorithm should be used to optimize the calculation of gIQ is still debated. The aim of our study was to compare seven different free-access resistance algorithms and their derived gIQs as predictors of 48 week virological response to darunavir-based salvage therapy in the clinical setting. METHODS: patients placed on two nucleoside reverse transcriptase inhibitors + 600/100 mg of darunavir/ritonavir twice daily  ±â€Š enfuvirtide were prospectively evaluated. Virological response was assessed at 48 weeks. Darunavir resistance interpretation was performed according to seven different algorithms, of which two were weighted algorithms. Analysis of other factors potentially associated with virological response at 48 weeks was performed. RESULTS: fifty-six treatment-experienced patients were included. Overall, 35 patients (62.5%) had a virological response at 48 weeks. Receiver operator characteristic curve analysis showed that De Meyer's weighted score (WS) and its derived gIQ (gIQ WS) were the most accurate parameters defining virological response, and related cut-offs showed the best sensitivity/specificity pattern. In univariate logistic regression analysis, baseline log viral load (P = 0.028), optimized background score ≥ 2 (P = 0.048), WS >5 (P = 0.001) and WS gIQ ≥ 600 (P < 0.0001) were independently associated with virological response. In multivariate analysis, only baseline log viral load (P = 0.008) and WS gIQ ≥ 600 (P < 0.0001) remained in the model. CONCLUSIONS: in our study, although different resistance interpretation algorithms and derived gIQs were associated with virological response, gIQ WS was the most accurate predictive model for achieving a successful virological response.

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 µmol/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.

Development, validation, and routine application of a high-performance liquid chromatography method coupled with a single mass detector for quantification of itraconazole, voriconazole, and posaconazole in human plasma.

We have developed and validated a high-performance liquid chromatography method coupled with a mass detector to quantify itraconazole, voriconazole, and posaconazole using quinoxaline as the internal standard. The method involves protein precipitation with acetonitrile. Mean accuracy (percent deviation from the true value) and precision (relative standard deviation percentage) were less than 15%. Mean recovery was more than 80% for all drugs quantified. The lower limit of quantification was 0.031 microg/ml for itraconazole and posaconazole and 0.039 microg/ml for voriconazole. The calibration range tested was from 0.031 to 8 microg/ml for itraconazole and posaconazole and from 0.039 to 10 microg/ml for voriconazole.

Population pharmacokinetic modeling of the association between 63396C->T pregnane X receptor polymorphism and unboosted atazanavir clearance.

Atazanavir (ATV) plasma concentrations are influenced by CYP3A4 and ABCB1, which are regulated by the pregnane X receptor (PXR; NR1I2). PXR expression is correlated with CYP3A4 in liver in the absence of enzyme inducers. The PXR single nucleotide polymorphism (SNP) 63396C→T (rs2472677) alters PXR expression and CYP3A4 activity in vitro, and we previously showed an association of this polymorphism with unboosted ATV plasma concentrations. The aim of this study was to develop a population pharmacokinetic analysis to quantify the impact of 63396C→T and diurnal variation on ATV clearance. A population analysis was performed with 323 plasma samples from 182 randomly selected patients receiving unboosted ATV. Two hundred fifty-nine of the blood samples were collected at random time points, and 11 patients had a full concentration-time profile at steady state. Nonlinear mixed effects modeling was applied to explore the effects of PXR 63396C→T, patient demographics, and diurnal variation. A one-compartment model with first-order absorption and lag time best described the data. Population clearance was 19.7 liters/h with interpatient variability or coefficient of variation (CV) of 21.5%. Homozygosity for the T allele for PXR 63396 was associated with a 17.0% higher clearance that was statistically significant. Evening dosing was associated with 34% higher bioavailability than morning dosing. Patient demographic factors had no effect on ATV clearance. These data show an association of PXR 63396C→T and diurnal variation on unboosted ATV clearance. The association is likely to be mediated through an effect on hepatic PXR expression and therefore expression of its target genes (e.g., CYP3A4, SLCO1B1, and ABCB1), which are known to be involved in ATV clearance.