Population pharmacokinetics and probability of target attainment of meropenem in critically ill patients.

PURPOSE: Patients admitted to intensive care unit (ICU) with Klebsiella pneumoniae infections are characterized by high mortality. The aims of the present study were to investigate the population pharmacokinetics parameters and to assess the probability of target attainment of meropenem in critically ill patients to provide information for more effective regimens. METHODS: Twenty-seven consecutive patients were included in the study. Meropenem was administered as 3-h intravenous (i.v.) infusions at doses of 1-2 g every 8 or 12 h. Meropenem plasma concentrations were measured by a high-performance liquid chromatography (HPLC) method, and a population pharmacokinetics analysis was performed using NONMEM software. Meropenem plasma disposition was simulated for extended (3 h; 5 h) or continuous i.v. infusions, and the following parameters were calculated: time during which free drug concentrations were above minimum inhibitory concentration (MIC) (fT > MIC), free minimum plasma concentrations above 4× MIC (fCmin > 4× MIC), probability of target attainment (PTA), and cumulative fraction of response (CFR). RESULTS: Gender and severity of sepsis affected meropenem clearance, whose typical population values ranged from 6.22 up to 12.04 L/h (mean ± standard deviation (SD) value, 9.38 ± 4.47 L/h). Mean C min value was 7.90 ± 7.91 mg/L, suggesting a high interindividual variability. The simulation confirmed that 88 and 97.5 % of patients achieved effective C min > 4× MIC values after 3- and 5-h i.v. infusions of meropenem 2 g × 3/day, respectively. On the contrary, the same total daily doses reached the target C min > 4× MIC values in 100 % of patients when administered as continuous i.v. infusions. CONCLUSIONS: Several factors may influence meropenem pharmacokinetics in ICU patients. Continuous i.v. infusions of meropenem seem to be more effective than standard regimens to achieve optimal therapeutic targets.

Pharmacogenetics of BCR/ABL Inhibitors in Chronic Myeloid Leukemia.

Chronic myeloid leukemia was the first haematological neoplasia that benefited from a targeted therapy with imatinib nearly 15 years ago. Since then, several studies have investigated the role of genes, their variants (i.e., polymorphisms) and their encoded proteins in the pharmacokinetics and pharmacodynamics of BCR-ABL1 tyrosine kinase activity inhibitors (TKIs). Transmembrane transporters seem to influence in a significant manner the disposition of TKIs, especially that of imatinib at both cellular and systemic levels. In particular, members of the ATP-binding cassette (ABC) family (namely ABCB1 and ABCG2) together with solute carrier (SLC) transporters (i.e., SLC22A1) are responsible for the differences in drug pharmacokinetics. In the case of the newer TKIs, such as nilotinib and dasatinib, the substrate affinity of these drugs for transporters is variable but lower than that measured for imatinib. In this scenario, the investigation of genetic variants as possible predictive markers has led to some discordant results. With the partial exception of imatinib, these discrepancies seem to limit the application of discovered biomarkers in the clinical settings. In order to overcome these issues, larger prospective confirmative trials are needed.

Case report of a successful treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia and MRSA/vancomycin-resistant Enterococcus faecium cholecystitis by daptomycin.

A 72-year-old man, receiving 8 mg daptomycin/kg body weight/day for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, was diagnosed with MRSA/vancomycin-resistant Enterococcus faecium (VRE) cholecystitis (daptomycin MIC values, 1 and 2 mg/liter, respectively). After the fifth drug dose, the bile concentration of daptomycin was 66 mg/liter 5 min after drug administration, with the biliary concentration/MIC values higher than 30 for both bacterial strains. Therefore, daptomycin achieved therapeutic levels in bile, hence suggesting a role for the drug in the treatment of MRSA/VRE cholecystitis.

Linezolid in the central nervous system: comparison between cerebrospinal fluid and plasma pharmacokinetics.

BACKGROUND: Linezolid is effective against methicillin-resistant Staphylococcus aureus, which may cause central nervous system (CNS) infections, but drug concentrations in plasma are characterized by a large inter-patient variability. Therefore, the present study was aimed at evaluating linezolid pharmacokinetics in plasma and cerebrospinal fluid (CSF) in 7 patients with external ventricular drainage, who received linezolid 600 mg twice daily as 1-h intravenous infusion to prevent CNS infections. METHODS: Plasma and CSF linezolid concentrations were measured by high-performance liquid chromatography (HPLC) after the 1(st) and 5(th) dose, and pharmacokinetics were evaluated by non-compartmental analysis. RESULTS: Values of the CSF area under the time/concentration curve (AUC) (range 18.2-85.5 and 19.6-160.5 h × mg/l at the 1st and 5th dose, respectively) were lower than those calculated in plasma (range 27.6-224.0 and 27.5-166.1 h × mg/l, respectively). For minimum inhibitory concentration (MIC) = 1 mg/l, CSF AUC/MIC values were nearly equal to or greater than 100 only in 2 subjects after the 1st and 5th dose, whereas mean time above the MIC (T > MIC) values were higher than 75% in only 3 patients. Similar results were obtained when pharmacokinetic/pharmacodynamic parameters were evaluated in plasma. CONCLUSION: The present results suggest that changes in linezolid doses and measurement of drug concentrations should be considered as useful strategies to optimize treatment in some patients.

A rapid high-performance liquid chromatography method to measure linezolid and daptomycin concentrations in human plasma.

Daptomycin and linezolid, recently introduced to treat severe Gram-positive infections, are effective against multidrug-resistant Gram-positive microorganisms such as methicillin-resistant Staphylococcus aureus, methicillin-resistant Staphylococcus epidermidis, and vancomycin-resistant Enterococci bacteria that are less sensitive or frankly resistant, including methicillin-resistant S. aureus. However, alteration of their plasma profile has been described in some patients and this may be associated with toxicities or selection of resistant strains. The measurement of plasma concentrations of both drugs may allow the identification of those subjects at major risk of adverse events. Therefore, a rapid and sensitive high-performance liquid chromatography method for the analysis of daptomycin and linezolid was developed and applied in clinical settings. Drugs were extracted from plasma by adding methanol and, after centrifugation, clear supernatants were injected into the high-performance liquid chromatography system. Isocratic elution (1.5 mL/min) was performed using a mobile phase consisting of ammonium phosphate buffer 40 mM, pH 4.0, acetonitrile (70:30, vol/vol) through a BDS C8 Hypersil stationary phase (250 x 4.6 mm, 5 mum); ultraviolet detection was used at 214 nm. Linezolid and daptomycin eluted within 20 minutes from the injection, and mean recoveries ranged between 95.4% and 112.1%, respectively. The method was linear (coefficient of linearity, 0.998-0.999) over the full range of concentrations assayed, from 0.78125 mg/L (limit of quantitation) to 100 mg/L for both drugs. The Sy.x values were equal to 0.25 +/- 0.10 and 0.29 +/- 0.18 mg/L for daptomycin and linezolid, respectively. Precision values were lower than 20% over the entire range of calibration standard, and accuracy was within the range of 80% to 120% for all concentrations. The present method proved to be sensitive and specific to measure daptomycin and linezolid plasma concentrations in patients affected by severe Gram-positive infections, allowing therapeutic drug monitoring in those patients at major risk of severe adverse events.

Association of the hOCT1/ABCB1 genotype with efficacy and tolerability of imatinib in patients affected by chronic myeloid leukemia.

PURPOSE: The present study was aimed at investigating whether imatinib pharmacogenetics is related to its pharmacodynamics in patients affected by chronic myeloid leukemia. METHODS: Through a procedure based on a sequence of classical statistics methods, we investigated the possible relationships between treatment efficacy/tolerability and combinations of time-independent variables as gender and genetic covariates in the form of single nucleotide polymorphisms (SNPs) or combinations thereof. Moreover, since the drug tolerability has a strong incidence on the discontinuation of the therapy, we investigated whether the time of manifestation of the most frequent toxic effects can be related to time-independent patients' characteristics or not. RESULTS: We found that a combination of two polymorphisms, namely hOCT1 c.480C>G (rs683369) and ABCB1 c.3435C>T (rs1045642), seems to play the role of predictor for imatinib in both efficacy and toxicity. Furthermore, the time of manifestation of edema toxicity is found to be associated to a combination of gender and ABCB1 c.3435C>T, whereas the time of manifestation of cramp toxicity appears related to gender. CONCLUSIONS: The novelty of this study is dual: the achievement of results that potentially have a significant clinical interest and the demonstration that the adoption of composed covariates may represent a unique tool to study different aspects of the treatment with imatinib.

Methods: for studying pharmacogenetic profiles of combination chemotherapeutic drugs.

INTRODUCTION: Molecular and genetic analysis of tumors and individuals has led to patient-centered therapies, through the discovery and identification of genetic markers predictive of drug efficacy and tolerability. Present therapies often include a combination of synergic drugs, each of them directed against different targets. Therefore, the pharmacogenetic profiling of tumor masses and patients is becoming a challenge, and several questions may arise when planning a translational study. AREAS COVERED: The review presents the different techniques used to stratify oncology patients and to tailor antineoplastic treatments according to individual pharmacogenetic profiling. The advantages of these methodologies are discussed as well as current limits. EXPERT OPINION: Facing the rapid technological evolution for genetic analyses, the most pressing issues are the choice of appropriate strategies (i.e., from gene candidate up to next-generation sequencing) and the possibility to replicate study results for their final validation. It is likely that the latter will be the major obstacle in the future. However, the present landscape is opening up new possibilities, overcoming those hurdles that have limited result translation into clinical settings for years.

Polycomb genes are associated with response to imatinib in chronic myeloid leukemia.

AIM: Imatinib is a tyrosine kinase inhibitor that has revolutionized the treatment of chronic myeloid leukemia (CML). Despite its efficacy, about a third of patients discontinue the treatment due to therapy failure or intolerance. The rational identification of patients less likely to respond to imatinib would be of paramount clinical relevance. We have shown that transmembrane transporter hOCT1 genotyping predicts imatinib activity. In parallel, Polycomb group genes (PcGs) are epigenetic repressors implicated in CML progression and in therapy resistance. PATIENTS & METHODS: We measured the expression of eight PcGs in paired pre- and post-imatinib bone marrow samples from 30 CML patients. RESULTS: BMI1, PHC3, CBX6 and CBX7 expression was significantly increased during imatinib treatment. Post-treatment levels of CBX6 and CBX7 predicted 3-month response rate. Measurement of post-treatment BMI1 levels improved the predictive power of hOCT1 genotyping. CONCLUSION: These results suggest that the expression levels of PcGs might be useful for a more accurate risk stratification of CML patients.

Population pharmacokinetics of daptomycin in patients affected by severe Gram-positive infections.

A population pharmacokinetic analysis of daptomycin was performed based on therapeutic drug monitoring (TDM) data from 58 patients receiving doses of 4-12 mg/kg for the treatment of severe Gram-positive infections. At a daily dose of 8 mg/kg, daptomycin plasma concentrations (mean ± S.D.) were 76.9 ± 9.8 mg/L at the end of infusion and 52.7 ± 15.4 mg/L and 11.4 ± 5.4 mg/L at 0.5 h and 23 h after drug administration, respectively. The final model was a one-compartmental model with first-order elimination, with estimated clearance (CL) of 0.80 ± 0.14 L/h and a volume of distribution (V(d)) of 0.19 ± 0.05 L/kg. Creatinine clearance (CL(Cr)) was identified as having a significant influence on daptomycin CL, and a decrease in CL(Cr) of 30 mL/min from the median value (80 mL/min) was associated with a reduction of daptomycin CL from 0.80 L/h to 0.73 L/h. These results confirm that the presence of severe infection may be associated with an altered disposition of daptomycin, with an increased Vd. MICs were available in 41 patients and results showed that 38 and 31 subjects achieved AUC/MIC values associated with bacteriostatic (>400) and bactericidal effects (>800), respectively. Of note, 31 of these 41 subjects experienced a clinical improvement or were cured. Although daptomycin pharmacokinetics may be influenced by infections, effective AUC/MIC values were achieved in the majority of patients. The present model may be applied in clinical settings for a TDM routine on the basis of a sparse blood sampling protocol.

Pharmacokinetic and pharmacogenetic predictive markers of irinotecan activity and toxicity.

After the rapid development of new classes of antineoplastic drugs, research activities have focused their efforts to the identification of predictive markers of drug activity and tolerability. Irinotecan (CPT-11) may induce severe toxicities (diarrhea, neutropenia) that limit its clinical use, but the increasing knowledge of its pharmacokinetics offered a potential approach to treatment optimization. Pharmacokinetics, the first area of investigation, has identified markers such as biliary index, the relative extent of conversion and the glucuronidation ratio, which are capable to define the risk for severe adverse effects. Because of the existence of some issues concerning the adoption of pharmacokinetic strategies to optimize CPT-11 dose and schedule, analyses of genetic polymorphisms seemed to offer a more reliable and safer approach for the identification of patients at risk than pharmacokinetics. In this view, the uridine diphosphate glucuronosil transferase isoform 1A1 (UGT1A1) was associated with significant changes in disposition of CPT-11 and its metabolites, and consequently with treatment-induced toxicities. However, the complex pharmacokinetics of irinotecan and the involvement of several enzymes other than UGT (i.e., carboxyl estherases, CYP450 isoforms), and transmembrane transporters (ABCB1, ABCC1, ABCG2, SLCO1B1) make difficult the identification of patients with an optimal sensitivity and specificity, and a large part of variability among patients still remains unexplained. Furthermore, prospective clinical studies that should demonstrate the reliability of those pharmacokinetic and pharmacogenetic markers are still lacking. In the present review, pharmacokinetic and pharmacogenetic markers will be discussed.