Showing papers in "Therapeutic Drug Monitoring in 2009"

Dried blood spot methods in therapeutic drug monitoring: methods, assays, and pitfalls.

Abstract: This article reviews dried blood spot (DBS) sampling in therapeutic drug monitoring. The DBS method involves applying whole blood obtained via a fingerprick to a sampling paper. After drying and transportation, the blood spot is extracted and analyzed in the laboratory. Assays of many medicines in DBS have already been reported in the literature and are reviewed here. The technique involved in and factors that may influence the accuracy and reproducibility of DBS methods are also discussed. DBS sampling ultimately seems to be a useful technique for therapeutic drug monitoring that could have many advantages in comparison with conventional venous sampling. However, its benefits must be weighed against the degree of potential errors introduced via the sampling method; there is evidently a need for more standardization, quality assurance, basic research, and assay development.

Opportunities to optimize tacrolimus therapy in solid organ transplantation: report of the European consensus conference.

Abstract: In 2007, a consortium of European experts on tacrolimus (TAC) met to discuss the most recent advances in the drug/dose optimization of TAC taking into account specific clinical situations and the analytical methods currently available and drew some recommendations and guidelines to help clinicians with the practical use of the drug. Pharmacokinetic, pharmacodynamic, and more recently pharmacogenetic approaches aid physicians to individualize long-term therapies as TAC demonstrates a high degree of both between- and within-individual variability, which may result in an increased risk of therapeutic failure if all patients are administered a uniform dose. TAC has undoubtedly benefited from therapeutic drug monitoring, but interpretation of the blood concentration is confounded by the relative differences between the assays. Single time points, limited sampling strategies, and area under concentration-time curve have all been considered to determine the most appropriate sampling procedure that correlates with efficacy. Therapeutic trough TAC concentration ranges have changed since the initial introduction of the drug, while still maintaining adequate immunosuppression and avoiding drug-related adverse effects. Pharmacodynamic markers have also been considered advantageous to the clinician, which may better reflect efficacy and safety, taking into account the between-individual variability rather than whole blood concentrations. The choice of method, differences between methods, and potential pitfalls of the method should all be considered when determining TAC concentrations. The recommendations of this consensus meeting regarding the analytical methods include the following: encourage the development and promote the use of analytical methods displaying a lower limit of quantification (1 ng/mL), perform careful validation when implementing a new analytical assay, participate in external proficiency testing programs, promote the use of certified material as calibrators in high-performance liquid chromatography with mass spectrometric detection methods, and take account of the assay and intermethod bias when comparing clinical trial outcomes. It is also important to consider that TAC concentrations may also be influenced by other factors such as specific pharmacokinetic characteristics associated with the population, drug interactions, pharmacogenetics, adverse events that may alter TAC concentrations, and any change in the oral formulation that may result in pharmacokinetic changes. This meeting emphasized the importance of obtaining multicenter prospective trials to assess the efficacy of alternative strategies to TAC trough concentrations whether it is other single time points or area under the concentration-time curve Bayesian estimation using limited sampling strategies and to select, standardize, and validate routine biomarkers of TAC pharmacodynamics.

Methods for quantification of exposure to cigarette smoking and environmental tobacco smoke: focus on developmental toxicology.

Abstract: Active and passive smoking have been associated with an array of adverse effects on health. The development of valid and accurate scales of measurement for exposures associated with health risks constitutes an active area of research. Tobacco smoke exposure still lacks an ideal method of measurement. A valid estimation of the risks associated with tobacco exposure depends on accurate measurement. However, some groups of people are more reluctant than others to disclose their smoking status and exposure to tobacco. This is particularly true for pregnant women and parents of young children, whose smoking is often regarded as socially unacceptable. For others, recall of tobacco exposure may also prove difficult. Because relying on self-report and the various biases it introduces may lead to inaccurate measures of nicotine exposure, more objective solutions have been suggested. Biomarkers constitute the most commonly used objective method of ascertaining nicotine exposure. Of those available, cotinine has gained supremacy as the biomarker of choice. Traditionally, cotinine has been measured in blood, saliva, and urine. Cotinine collection and analysis from these sources has posed some difficulties, which have motivated the search for a more consistent and reliable source of this biomarker. Hair analysis is a novel, noninvasive technique used to detect the presence of drugs and metabolites in the hair shaft. Because cotinine accumulates in hair during hair growth, it is a unique measure of long-term, cumulative exposure to tobacco smoke. Although hair analysis of cotinine holds great promise, a detailed evaluation of its potential as a biomarker of nicotine exposure, is needed. No studies have been published that address this issue. Because the levels of cotinine in the body are dependent on nicotine metabolism, which in turn is affected by factors such as age and pregnancy, the characterization of hair cotinine should be population specific. This review aims at defining the sensitivity, specificity, and clinical utilization of different methods used to estimate exposure to cigarette smoking and environmental tobacco smoke.

New insights into the pharmacokinetics and pharmacodynamics of the calcineurin inhibitors and mycophenolic acid: possible consequences for therapeutic drug monitoring in solid organ transplantation

Abstract: Although therapeutic drug monitoring (TDM) of immunosuppressive drugs has been an integral part of routine clinical practice in solid organ transplantation for many years, ongoing research in the field of immunosuppressive drug metabolism, pharmacokinetics, pharmacogenetics, pharmacodynamics, and clinical TDM keeps yielding new insights that might have future clinical implications. In this review, the authors will highlight some of these new insights for the calcineurin inhibitors (CNIs) cyclosporine and tacrolimus and the antimetabolite mycophenolic acid (MPA) and will discuss the possible consequences. For CNIs, important relevant lessons for TDM can be learned from the results of 2 recently published large CNI minimization trials. Furthermore, because acute rejection and drug-related adverse events do occur despite routine application of CNI TDM, alternative approaches to better predict the dose-concentration-response relationship in the individual patient are being explored. Monitoring of CNI concentrations in lymphocytes and other tissues, determination of CNI metabolites, and CNI pharmacogenetics and pharmacodynamics are in their infancy but have the potential to become useful additions to conventional CNI TDM. Although MPA is usually administered at a fixed dose, there is a rationale for MPA TDM, and this is substantiated by the increasing knowledge of the many nongenetic and genetic factors contributing to the interindividual and intraindividual variability in MPA pharmacokinetics. However, recent, large, randomized clinical trials investigating the clinical utility of MPA TDM have reported conflicting data. Therefore, alternative pharmacokinetic (ie, MPA free fraction and metabolites) and pharmacodynamic approaches to better predict drug efficacy and toxicity are being explored. Finally, for MPA and tacrolimus, novel formulations have become available. For MPA, the differences in pharmacokinetic behavior between the old and the novel formulation will have implications for TDM, whereas for tacrolimus, this probably will not to be the case.

Relationship Between Oral Fluid and Blood Concentrations of Drugs of Abuse in Drivers Suspected of Driving Under the Influence of Drugs

Abstract: In recent years, the interest in the use of oral fluid as a biological matrix has increased significantly, particularly for detecting driving under the influence of drugs (DUID). In this study, the relationship between the oral fluid and the blood concentrations of drugs of abuse in drivers suspected of DUID is discussed. Blood and oral fluid samples were collected from drivers suspected of DUID or stopped during random controls by the police in Belgium, Germany, Finland, and Norway for the ROSITA-2 project. The blood samples were analyzed by gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS), sometimes preceded by immunoassay screening of blood or urine samples. The oral fluid samples were analyzed by GC-MS or LC-MS(/MS). Scatter plots and trend lines of the blood and oral fluid concentrations and the median, mean, range, and SD of the oral fluid to blood (OF:B) ratios were calculated for amphetamines, benzodiazepines, cocaine, opiates, and Delta(9)-2 tetrahydrocannabinol. The ratios found in this study were comparable with those that were published previously, but the range was wider. The OF:B ratios of basic drugs such as amphetamines, cocaine, and opiates were >1 [amphetamine: median (range) 13 (0.5-182), methylenedioxyamphetamine: 4 (1-15), methylenedioxymethamphetamine: 6 (0.9-88), methamphetamine: 5 (2-23), cocaine: 22 (4-119), benzoylecgonine: 1 (0.2-11), morphine: 2 (0.8-6), and codeine: 10 (0.8-39)]. The ratios for benzodiazepines were very low, as could be expected as they are highly protein bound and weakly acidic, leading to low oral fluid concentrations [diazepam: 0.02 (0.01-0.15), nordiazepam: 0.04 (0.01-0.23), oxazepam: 0.05 (0.03-0.14), and temazepam: 0.1 (0.06-0.54)]. For tetrahydrocannabinol, an OF:B ratio of 15 was found (range 0.01-569). In this study, the time of last administration, the dose, and the route of administration were unknown. Nevertheless, the data reflect the variability of the OF:B ratios in drivers thought to be under the influence of drugs. The wide range of the ratios, however, does not allow reliable calculation of the blood concentrations from oral fluid concentrations.

Robust, high-throughput LC-MS/MS method for therapeutic drug monitoring of cyclosporine, tacrolimus, everolimus, and sirolimus in whole blood

Abstract: The authors describe a fast, robust, and straightforward liquid chromatography and tandem mass spectrometry (LC-MS/MS) method with the use of a single LC-MS/MS system for cyclosporine A, tacrolimus, sirolimus, and everolimus in whole blood. The purpose of this method was to replace the immunoassay (IA) methods used in the laboratory of a hospital performing most organ transplantations (including heart, lung, liver, kidneys, bone marrow, and intestinal tract). Several LC-MS/MS methods have been described so far; however, most of them require complicated online extraction procedures. The described LC-MS/MS method uses a chromatographic gradient in combination with protein precipitation as sample preparation. The chromatographic method is capable of separating otherwise interfering peaks, with an analysis time of 2.6 minutes. Analyses were performed on a triple quadrupole LC-MS/MS system, with a C18 column held at 60 degrees C. Sample preparation required only 1 precipitation/dilution step. Sirolimus and everolimus are prepared and measured separately from tacrolimus and cyclosporine. During method development, it was found that the use of zinc sulfate provides process efficiency results of about 100% for tacrolimus and cyclosporine A, but only 81% and 87% for sirolimus and everolimus, respectively. With the developed sample preparation without zinc sulfate for sirolimus and everolimus, process efficiencies were 99% and 108%, respectively. The methods have been fully validated, and in a comparative study, patient samples were analyzed with IA and our developed LC-MS/MS methods. In the comparative studies, correlations (R2 values) of more than 0.85 were found between the IA and the new LC-MS/MS patient blood levels. There was a systematic deviation in blood levels measured by LC-MS/MS compared with IAs for cyclosporine A (17% lower than with immunoassay) and everolimus (30% lower than with IA). There seemed to be little or no systematic deviation for sirolimus and tacrolimus. The controls determined by the LC-MS/MS method over the past 10 months showed coefficient of variations of no more than 8.0% for each of the 4 immunosuppressants. In conclusion, the authors found the developed methods to be cost saving, more flexible, and more sensitive and that these methods have larger linear ranges than the previously used IA methods. The methods are already used for more than 20,000 patient samples in the daily routine, analyzing approximately 70 patient samples per day.

Explaining variability in tacrolimus pharmacokinetics to optimize early exposure in adult kidney transplant recipients.

Abstract: To prevent acute rejection episodes, it is important to reach adequate tacrolimus (TRL) exposure early after kidney transplantation. With a better understanding of the high variability in the pharmacokinetics of TRL, the starting dose can be individualized, resulting in a reduction in dose adjustments to obtain the target exposure. A population pharmacokinetic analysis was performed to estimate the effects of demographic factors, hematocrit, serum albumin concentration, prednisolone dose, TRL dose interval, polymorphisms in genes coding for ABCB1, CYP3A5, CYP3A4, and the pregnane X receptor on TRL pharmacokinetics. Pharmacokinetic data were prospectively obtained in 31 de novo kidney transplant patients randomized to receive TRL once or twice daily, and subsequently, the data were analyzed by means of nonlinear mixed-effects modeling. TRL clearance was 1.5-fold higher for patients with the CYP3A5*1/*3 genotype compared with the CYP3A5*3/*3 genotype (5.5 +/- 0.5 L/h versus 3.7 +/- 0.3 L/h, respectively). This factor explained 30% of the interindividual variability in apparent clearance (exposure). Also, a relationship between the pregnane X receptor A+7635G genotype and TRL clearance was identified with a clearance of 3.9 +/- 0.3 L/h in the A allele carriers versus 5.4 +/- 0.6 L/h in the GG genotype. Finally, a concomitant prednisolone dose of more than 10 mg/d increased the TRL apparent clearance by 15%. In contrast, body weight was not related to TRL clearance in this population. Because patients are typically dosed per kilogram body weight, this might result in underexposure and overexposure in patients, with a low and high body weight, respectively. This integrated analysis shows that adult renal transplant recipients with the CYP3A5*1/*3 genotype require a 1.5 times higher, fixed, starting dose compared with CYP3A5*3/*3 to reach the predefined target exposure early after transplantation.

Serum concentrations of antidepressant drugs in a naturalistic setting: compilation based on a large therapeutic drug monitoring database.

Abstract: A compilation of therapeutic drug monitoring data for 15 antidepressant drugs in a naturalistic routine clinical setting is presented. A substantial number of serum concentrations, at different daily doses, are outlined, and the intraindividual and overall serum concentration coefficient of variation for a respective substance is presented. Also, concentration comparisons between women and men, and patients older or younger than 65 years are made. The drugs included are amitriptyline (n = 394), citalopram (n = 5457), clomipramine (n = 400), escitalopram (n = 3066), fluoxetine (n = 793), fluvoxamine (n = 165), mianserin (n = 1063), mirtazapine (n = 1427), moclobemide (n = 200), nortriptyline (n = 206), paroxetine (n = 1677), reboxetine (n = 85), sertraline (n = 2998), trimipramine (n = 158), and venlafaxine (n = 1781). Of the 9 drugs exhibiting linear (first order) kinetics, all but reboxetine gave a significant negative dose-to-dose-normalized correlation with concentrations, that is an increased clearance with higher dose. When dose was correlated to the metabolite:parent substance ratio for drugs exhibiting linear kinetics, citalopram and mianserin gave a positive slope, contrary to a negative slope shown for sertraline and venlafaxine. The intraindividual variations of the serum concentrations were lower than the overall variations, and the intraindividual variation of the metabolite:parent substance ratio was lower than the intraindividual variation of respective parent substance (except clomipramine and mianserin). Women had significantly higher serum concentrations than men (significant for citalopram, escitalopram, mianserin, mirtazapine, and venlafaxine), and patients older than 65 years had higher serum concentrations than the younger ones for all drugs except amitriptyline, moclobemide, and trimipramine. By presenting a comprehensive compilation of therapeutic drug monitoring data for each drug, a reference tool is created, in addition to improved pharmacokinetic knowledge of antidepressant drugs.

Pharmacokinetic analysis of capsaicin after topical administration of a high-concentration capsaicin patch to patients with peripheral neuropathic pain.

Abstract: Capsaicin, a pungent compound in chili peppers, is a highly selective agonist for the transient receptor potential vanilloid 1 receptor expressed in nociceptive sensory nerves. A high-concentration (640 microg/cm2) capsaicin patch, designated NGX-4010, is in clinical evaluation for the management of peripheral neuropathic pain. To determine systemic capsaicin exposure after single 60- or 90-minute NGX-4010 applications, plasma samples were collected from 173 patients with postherpetic neuralgia (PHN), painful human immunodeficiency virus-associated neuropathy (HIV-AN), and painful diabetic neuropathy (PDN). The percentages of patients with quantifiable levels of capsaicin at any time point were 31% for PHN (30 of 96), 7% for HIV-AN (3 of 44), and 3% for PDN (1 of 33). The maximum plasma concentration observed in any patient was 17.8 ng/mL. Due to the limited number of quantifiable levels, a population analysis was performed to characterize the pharmacokinetics (PK) of capsaicin. Plasma concentrations were fitted adequately using a 1-compartment model with first-order absorption and linear elimination. Capsaicin levels declined very rapidly, with a mean population elimination half-life of 1.64 hours. Mean area under the curve and C max values after a 60-minute application were 7.42 ng x h/mL and 1.86 ng/mL, respectively. Only a few correlations between calculated PK parameters and patient characteristics were observed. Duration and area of application of the patch were detected as significant covariates explaining the PK of capsaicin. Ninety-minute applications of NGX-4010 resulted in capsaicin area under the curve and Cmax values approximately 1.78- and 2.15-fold higher than those observed in patients treated for 60 minutes. Treatment on the feet (patients with HIV-AN and PDN) produced far lower systemic exposure than treatment on the trunk (patients with PHN). Finally, larger treatment areas were associated with statistically higher Vc/F values. The low systemic exposure and very rapid elimination half-life of capsaicin after NGX-4010 administration are unlikely to result in systemic effects and support the overall safety profile of this investigational cutaneous patch.

An enzyme-linked immunosorbent assay for therapeutic drug monitoring of cetuximab.

Abstract: Cetuximab is an anti-epidermal growth factor receptor monoclonal antibody used in the treatment of colorectal and head and neck cancers. Part of the interindividual differences in response may be explained by interindividual variability in pharmacokinetics. An assay measuring cetuximab serum concentrations is therefore needed. An enzyme-linked immunosorbent assay was developed using microtiter plates sensitized with a recombinant human epidermal growth factor receptor extracellular domain. Lower and upper limits of quantitation and limit of detection were determined. Eight standard calibrators (SCs) and 3 quality controls (QCs), that is, 0.75, 7.5, and 15 mg/L, were tested on 5 occasions on 1 day and on 5 occasions on different days. Trough and peak serum concentrations of cetuximab were measured in 15 patients with metastatic colorectal cancer and 1 patient with undetermined neoplasia undergoing cetuximab-based chemotherapy. Cetuximab concentrations were described using a 2-compartment population pharmacokinetic model. Imprecision and accuracy of SC and QC were < or = 20%, except for the 0 and 0.1 mg/L SC concentrations (< or = 20%). The limit of detection was 0.012 mg/L. Lower and upper limits of quantitation were 0.75 and 15 mg/L, respectively. A total number of 198 blood samples were available from the 16 patients. Median (range) trough and peak concentrations during the treatment were 49.6 (5.8-105.4) and 177.2 (97.5-235) mg/L, respectively. This method is rapid, accurate, and reproducible and may be useful for pharmacokinetic and pharmacokinetic-pharmacodynamic studies, as well as in therapeutic drug monitoring of cetuximab.

Multi-site analytical evaluation of the Abbott ARCHITECT tacrolimus assay

Abstract: The objective of this study was to evaluate the analytical performance of the Abbott ARCHITECT Tacrolimus immunoassay. Proficiency panels and specimens from a population of organ transplant recipients were analyzed in 6 clinical laboratories in Europe and the United States, and the results were compared with other methods. The ARCHITECT assay requires a whole blood specimen pretreatment step with methanol/zinc sulfate to precipitate protein and extract the drug, followed by a 30-minute immunoassay using anti-tacrolimus antibody-coated paramagnetic microparticles and an acridinium-tacrolimus tracer. The assay was free from hematocrit interference in the range 25%-55% and from interference by extremes of cholesterol, triglycerides, bilirubin, total protein, and uric acid. The total percent of coefficient of variations of the assay were 4.9%-7.6% at 3 ng/mL, 2.9%-4.6% at 8.6 ng/mL, and 3.1%-8.2% at 15.5 ng/mL. Limit of detection was /=0.90 on all method comparisons. The ARCHITECT Tacrolimus assay is a semiautomated, robust, and highly sensitive immunoassay, representing an alternative approach for laboratories not equipped with LC-MSMS, and meets the 1 ng/mL recommendation of LOQ by the European Consensus Conference on Tacrolimus Optimization.

Trough tacrolimus concentrations in the first week after kidney transplantation are related to acute rejection.

Abstract: There is evidence showing the importance of reaching immunosuppressant target concentrations as soon as possible. The aim of this study was to evaluate the relationship between tacrolimus trough concentrations within the first week after transplantation and the rate of acute rejection. In this descriptive-analytic study, we included 57 renal transplant patients receiving tacrolimus as the primary immunosuppressive drug. After univariate analysis, donor age, duration of hospital stay, and creatinine clearance (third month) showed significant differences between rejecters and nonrejecters. In addition, mean tacrolimus trough concentrations on day 5, day 7, mean of days 1-7, and mean of days 5-7 were found to be significantly lower in rejecters (P = 0.009, P = 0.012, P = 0.006, and P = 0.035, respectively). Receiver operating characteristic curve analysis with tacrolimus trough concentrations measured on days 5 and 7 was able to discriminate between patients with and without acute rejection (P = 0.028 and P = 0.048 after Bonferroni correction). The tacrolimus trough concentration with the best sensitivity-specificity balance was 9.3 ng/mL on day 5 and 8.7 ng/mL on day 7. In the Kaplan-Meier analysis, patients with tacrolimus trough concentrations below 9.3 mg/mL on day 5 showed a lower survival time without acute rejection (P = 0.048 after correction) in comparison with patients with tacrolimus trough concentrations above this concentration. After logistic regression, we obtained a model relating rejection with sex, donor age, and tacrolimus trough concentrations on day 5 (P = 0.004). No significant relationship between tacrolimus trough concentrations and delta creatinine clearance from week 1 to month 3 was obtained. These results confirm that tacrolimus trough concentrations during the first week are an important predictor of acute rejection. Therefore, it is critical to reach target blood concentrations of tacrolimus as soon as possible to improve allograft survival.

A therapeutic drug monitoring algorithm for refining the imatinib trough level obtained at different sampling times.

Abstract: Background Correlation analyses have demonstrated that maintaining an adequate imatinib (IM) trough concentration would be important for clinical response in patients with chronic myeloid leukemia (CML) and Kit-positive gastrointestinal stromal tumors. The objectives of the current work were to use a pharmacokinetic model to refine the trough levels obtained at different sampling times and to propose a therapeutic drug monitoring algorithm and an acceptable sampling time window for imatinib trough sampling. Methods The pharmacokinetics of IM in patients (pts) with CML were characterized based on historical data from a Phase III study. In the elimination phase the concentration of IM (C(t)) follows a mono-exponential decline, and the standardized trough concentration (C(min,std) = C(tau)) can be described by a simple algorithm C(min,std) = C(t)* exp(k(e) x Delta t), where Delta t = t - tau, and tau is 24 hours for qd or 12 hours for bid dosing and k(e) is the elimination rate constant. The percent deviation of C(t) from C(min,std) was simulated for different Delta t and k(e) values to define a sampling time window Delta t, within which the percent deviation is Results Simulation analysis shows that C(t) is largely dependent on Delta t and k(e). The percent deviation of C(t) at 3 hours before or after tau from C(min,std) will be 7.1%, 13.1%, and 23.4% for pts with low, typical, and high k(e) values, 0.023/hour, 0.041/hour, and 0.070/hour, respectively. However, if a correction is made for C(t) by the algorithm using the typical k(e) value of 0.041 per hour, the percent deviation at 3 hours will be reduced to 5.3%, 0%, and 9.1% for pts with low, typical, and high k(e) values, respectively. Even if the sampling window is extended to +/-6 hours, the corresponding percent deviation will still be reasonable: 10.2%, 0%, and 19.0%, respectively. Conclusion By using the algorithm, the pharmacokinetic sampling window can be extended to a wider window to make the trough sampling easy to implement in the clinical setting, provided that the sampling time and dosing time are accurately recorded.

Influence of comedication on serum concentrations of aripiprazole and dehydroaripiprazole.

Abstract: Aripiprazole, a relatively new antipsychotic drug, is metabolized by cytochrome P450 3A4 (CYP3A4) and CYP2D6 to an active metabolite, dehydroaripiprazole. As studies on pharmacokinetic drug interactions with aripiprazole are so far limited, the aim of the present study was to investigate the impact of comedication on serum concentrations of aripiprazole and dehydroaripiprazole in psychiatric patients in a clinical setting. A therapeutic drug monitoring database was screened for patients receiving aripiprazole tablets as part of their treatment. Of the 361 samples included, 78% were from patients receiving comedication. The remaining 79 samples constituted the control group. Steady-state dose-adjusted serum concentrations (concentration to dose ratios, C:D ratios) of aripiprazole, dehydroaripiprazole and the sum of aripiprazole and dehydroaripiprazole, and the metabolic ratio (dehydroaripiprazole/aripiprazole) in the different comedication groups were compared with controls. Coadministration of a CYP3A4 inducer resulted in approximately 60% lower mean C:D ratios of aripiprazole, dehydroaripiprazole, and the sum of aripiprazole and dehydroaripiprazole (P < 0.05, P < 0.01, and P < 0.01, respectively). Combination with a CYP2D6 inhibitor resulted in a 45% higher mean C:D ratio of aripiprazole (P < 0.05), with no effect on the C:D ratio of dehydroaripiprazole. When aripiprazole was coadministered with alimemazine or lithium, a 56% (P < 0.01) and 43% (P = 0.05) higher mean C:D ratio of aripiprazole, respectively, was observed. Olanzapine, risperidone injections, escitalopram, or lamotrigine also had statistically significant effects on aripiprazole disposition but to a lesser extent. In conclusion, concurrent treatment with CYP3A4 inducers, CYP2D6 inhibitors, alimemazine, or lithium resulted in changes in the systemic exposure of aripiprazole between 40% and 60%. This is of such a magnitude that dose adjustments of aripiprazole may be required.

Defining a lowest observable adverse effect hair concentrations of mercury for neurodevelopmental effects of prenatal methylmercury exposure through maternal fish consumption: a systematic review.

Abstract: Background Methylmercury is an environmental pollutant that can cause irreversible effects on the development of children Although there is no doubt that high exposure can cause neurodevelopmental deficits, the threshold that will adversely affect the developing fetus is not well defined Our objective was to systematically review the evidence of neurodevelopmental risks of methylmercury to the unborn child from maternal fish consumption to define the lowest observable adverse effect hair concentration (LOAEHC) Methods A systematic review was conducted of all original research reporting on the effects of methylmercury on the human fetus A literature search was undertaken using SCOPUS, Medline-Ovid, PubMed, Google Scholar, and EMBASE Papers were selected based on the following inclusion criteria: 1) child neurodevelopmental outcome; 2) comparison groups; and 3) methylmercury exposure through fish consumption Results Forty-eight publications met these inclusion criteria Thirty articles reported on longitudinal studies and 18 were cross-sectional studies Variations in study design precluded formal meta-analysis Based on an evaluation of these studies, we defined the LOAEHC at 03 microg/g of maternal hair mercury The longitudinal studies yielded a LOAEHC of 05 microg/g Conclusion In the clinical context, the majority of pregnant women consume mercury-containing fish in amounts that are lower than the LOAEHC defined in this study However, the LOAEHC is in the same order of magnitude of mercury exposure that occurs in significant numbers of women Hence, although it appears safe to suggest that eating the recommended types and amounts of fish poses no measurable risks for neurodevelopmental deficits, analysis of hair mercury content before pregnancy might be suggested because dietary modification can decrease body content and risk

In vivo glucuronidation activity of drugs in neonates: extensive interindividual variability despite their young age.

Abstract: Compared with phase I isoenzymes, data on isoenzyme-specific phenotypic activity of uridine diphosphate glucuronosyltransferase (UGT) and its covariates in neonates are limited. In vivo observations on morphine, paracetamol (acetaminophen), and propofol disposition throughout childhood confirm the overall low-glucuronidation activity in neonates observed in in vitro studies. In addition to the phenotypic low-glucuronidation activity, in vivo observations of bilirubin (UGT1A1), morphine (UGT2B7), paracetamol (UGT1A6), and propofol (UGT1A9) glucuronidation in neonates display extensive interindividual variability, only in part explained by postmenstrual and postnatal age. Covariates like disease state characteristics (decreased morphine metabolism during therapeutic head cooling), genetic polymorphisms (UGT1A1 genetic variants and differences in bilirubin metabolism), or environmental factors (increased urinary excretion of paracetamol-glucuronide by repeated administration of paracetamol) further contribute to this variability. A focused approach to unveil covariates of the interindividual range is needed to improve our knowledge on drug disposition in early life.

Clozapine exposure and the impact of smoking and gender: A population pharmacokinetic study

Abstract: The primary objective of this study was to evaluate the magnitude and variability of concentration exposure to clozapine and norclozapine in a real-world clinical setting, with a focus on smoking status, using population pharmacokinetic methodologies. A retrospective review of plasma clozapine and norclozapine concentrations taken from inpatients at the Centre for Addiction and Mental Health, Toronto, from 2001 to 2007 was conducted. A nonlinear mixed-effects model was developed using NONMEM, including age, gender, weight, smoking status, and dosage formulation as covariates. Pharmacokinetic parameters and interindividual and residual variabilities were estimated with 1- and 2-compartment models. A total of 519 plasma clozapine concentrations from 197 patients (138 males; mean +/- SD age, 38 +/- 13 years; schizophrenia spectrum disorder 98.2%) were included for the analysis. A 1-compartment model with first-order absorption and elimination best described the data. Apparent volume of distribution was fixed to a previously reported value in the literature of 7 L/kg.The population-predicted oral clearance of clozapine and norclozapine was 18.0 and 39.0 L/h, respectively; both the predicted clearance values vary nearly 6-fold (range, 9.18-59.06 and 16.29-97.84 L/h, respectively). For clozapine, smokers and males showed increased oral clearance by 6.0 and 4.5 L/h, respectively. For norclozapine, smokers and male gender were associated with an increased oral clearance of 11.3 and 7.6 L/h, respectively. The formulation of clozapine administered had an impact on the absorption rate with a Ka of 0.14/h for tablet and 10.3/h for the suspension form.The data suggest that smoking and male gender are associated with lower exposure to clozapine and norclozapine due to the higher oral clearance. These findings may account for some of the variability in clozapine exposure and have important implications for individualized drug dosing and therapeutic drug monitoring.

Improved assay for the nonradioactive determination of inosine 5'-monophosphate dehydrogenase activity in peripheral blood mononuclear cells.

Abstract: Mycophenolic acid (MPA) inhibits the enzyme inosine 5'-monophosphate dehydrogenase (IMPDH). Thus, the measurement of IMPDH activity could serve as a specific pharmacodynamic (PD) tool for monitoring MPA therapy. At present, however, monitoring of pharmacokinetic parameters is preferred over that of PD parameters because, in general, PD assays are labor-intensive and poorly reproducible. Currently, cell count or protein concentration is widely accepted as methods to normalize enzyme activity. In the present study, we have attempted to further improve a method for the determination of IMPDH activity to increase the robustness and reproducibility of the IMPDH activity assay itself, without making the assay more labor-intensive. Therefore, several aspects of the IMPDH method were investigated regarding their influence on the reproducibility and also modified to increase the feasibility and consistency of the assay. The isolation of peripheral blood mononuclear cells (PBMCs) of whole blood samples was found to be the most variable step. Normalization on cell count is labor-intensive and at the same time has a poor reproducibility. Determination of the protein content in cell extracts is impaired by contamination with extracellular proteins and non-PBMCs. Alternatively, the intracellular substance adenosine monophosphate (AMP) was investigated to normalize the newly generated xanthosine monophosphate. Among various subject groups, no significant differences in mean AMP concentration were found. To simplify the procedure, PBMCs were diluted to a fixed volume after isolation from sample of whole blood, and the IMPDH activity was normalized to the AMP concentration quantified in the same high-performance liquid chromatography run as xanthosine monophosphate was quantified. The within-run and total imprecision (coefficient of variation) ranged from 4.2% to 10.6% and from 6.6% to 11.9%, respectively. In conclusion, the modified method described here for the measurement of IMPDH activity can be used reliably in multicenter trials and in longitudinal studies to evaluate the additional value of any PD monitoring among a diversity of patients treated with MPA.

Pharmacokinetics and therapeutic drug monitoring of psychotropic drugs in pediatrics.

Abstract: Therapeutic drug monitoring (TDM) in pediatrics (0-14 years) is especially important because the absorption, distribution, metabolism, and excretion of drugs and drug pharmacokinetic profiles can be different from that of the adult population. In this context, several parameters like half-life of drug elimination from the body (t(1/2)), peak plasma concentration (Cmax), area under the curve, clearance (CL), Tmax, and dose/concentration relationship in children may differ from adults. Hence, the knowledge of pharmacokinetic parameters and therapeutic and toxic ranges of drug concentrations may help the clinicians to optimize drug treatment regimens in the pediatric population. TDM of psychotropic drugs requires particular attention for the pharmacological and clinical consequences of nonadequate dose use, lack in the compliance, and overdoses with possible toxic effects. Psychoactive drugs such as benzodiazepines, antiepileptic drugs, tricyclic antidepressants, selective serotonin reuptake inhibitors, antipsychotic drugs, psychostimulants (attention-deficit hyperactivity disorder drugs), opioid analgesics, and antimigraine drugs are a heterogeneous group. These drugs are subject to interindividual variability, and therefore, the usefulness of TDM for these drugs has to be assessed individually. Because of the occurrence of comorbid pathologies, including psychiatric disorders, the use of combined pharmacotherapy is not uncommon. As a consequence, these patients may be at risk from a number of potential drug-drug interactions. The implementation of TDM in pediatric population is more difficult than in adults because some sampling procedures are invasive and cause discomfort in children, and additionally, they require the cooperation of the patient. Several examples will be provided where the use of alternative matrices, such as saliva, is proposed to minimize inconvenience and patient discomfort.

Validation of a liquid chromatography-mass spectrometric assay for tacrolimus in peripheral blood mononuclear cells.

Abstract: As a potential alternative to whole-blood tacrolimus (TAC) monitoring, a sensitive and selective method was developed for quantifying this immunosuppressant in human peripheral blood mononuclear cell population (PBMCs). These cells, expected to be a more specific biological matrix than whole blood to reflect pharmacological efficacy, could be promising for TAC therapeutic drug monitoring (TDM). The assay was developed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). PBMCs are isolated from 7 mL whole blood by centrifugation over Ficoll gradient density and washed twice with phosphate-buffered saline at 4 degrees C. Harvested cells were suspended within 1.5 mL of phosphate-buffered saline. Cell counts were performed to express and normalize TAC amount per 10 cells. TAC was extracted by a liquid-liquid extraction in basic medium (NH4OH) with 1-chlorobutane, and ascomycin was used as internal standard. After evaporation of the supernatant under nitrogen, the residue was reconstituted in methanol (MeOH). Compounds were eluted on a C18 column by a mixture of acetonitrile/water (90/10, vol/vol) containing 0.1% formic acid and 2 mmol/L of ammonium acetate. TAC and internal standard were monitored by detecting specific ammoniated product ions using multiple reaction monitoring acquisition mode in electrospray positive ionization. This method was fully validated in the range of 0.01-5 ng/mL. Limit of detection and of quantification are 0.005 and 0.01 ng/mL, respectively. Intra-assay and interassay recoveries ranged from 89.2% to 114.3% and 85.3% to 103.9%, respectively. Intra-assay and interassay imprecisions ranged from 9.3% to 12% and 10.7% to 12.2%, respectively, across the analytical range. Mean TAC extraction efficiency was 80.9% +/- 8.3%. Matrix effects were minimal with <8% ion suppression. This method is currently applied in clinical research protocols and allows the measurement of small intracellular amounts of TAC down to 0.006 ng per 10 PBMCs in kidney-transplanted recipients. This method could be a new potential tool for TAC TDM, providing new perspectives for optimizing immunosuppressive therapy. Further studies should be conducted to fully evaluate the benefit of intracellular TAC concentrations in refinement of TDM strategies for TAC to ensure optimal clinical outcomes.

Identification of prenatal amphetamines exposure by maternal interview and meconium toxicology in the Infant Development, Environment and Lifestyle (IDEAL) study.

Abstract: The Infant Development Environment and Lifestyle study is investigating the effects of prenatal methamphetamine (MAMP) exposure on infant and child development; potential concurrent exposure to cannabis and tobacco also are evaluated. Maternal self-reported drug use and/or meconium toxicology results defined drug exposure status. It is unclear how the frequency, duration, and magnitude of maternal MAMP exposure affect qualitative and quantitative meconium results. Interviews regarding maternal drug use were collected shortly after birth; meconium specimens were screened for amphetamines, cannabis, and cotinine by immunoassay and confirmed by gas chromatography mass spectrometry. The majority of MAMP- and cannabis-exposed infants were identified by maternal interview alone. Meconium tests were more likely to be positive if the mother reported MAMP and cannabis use, particularly in the third trimester. Less than half of immunoassay-positive amphetamines (31.0%) and cannabis (17.9%) meconium results were confirmed by gas chromatography mass spectrometry. Tobacco exposure was equally detected by immunoassay cotinine screening and maternal report. Meconium concentrations did not correlate with maternal self-report status or trimester of use or frequency or route of MAMP use. Maternal self-report was more sensitive than meconium testing for identifying MAMP and cannabis-exposed neonates; however, the timing of drug exposure may influence meconium toxicology results. Most women stopped MAMP and cannabis use before the third trimester. In the first trimester, meconium has not yet formed, and based on our recent results for opiates and cocaine, drug use in the second trimester appears to be poorly reflected in meconium. Low confirmation rates in meconium reinforce the need for confirmatory testing following positive screening results and additional research to identify alternative biomarkers.

Hair analysis of fatty acid ethyl esters in the detection of excessive drinking in the context of fetal alcohol spectrum disorders.

Abstract: A serious challenge in diagnosing fetal alcohol spectrum disorder (FASD) is the need to document alcohol use during pregnancy. Maternal/paternal alcohol abuse affects the likelihood of fetal alcohol exposure, and hence the occurrence of FASD. The objective of the current study was to document the use of the fatty acid ethyl ester (FAEE) hair test, a biomarker of excessive alcohol use, in parents at risk of having children with FASD and quantify the prevalence of alcohol use in this population. Hair samples submitted for FAEE testing between October 2005 and May 2007 were evaluated (n = 324). Subjects consisted of the parents of at-risk children. Samples were analyzed using a previously published method. Briefly, samples underwent a liquid-liquid extraction, followed by headspace solid phase microextraction, and were then analyzed by gas chromatography-mass spectrometry using deuterated FAEE as internal standards. Limit of detection and limit of quantification values were between 0.01-0.04 ng/mg and 0.04-0.12 ng/mg, respectively. Positive levels for excessive drinking were ascertained using a cutoff level of 0.5 ng/mg, offering 90% sensitivity and specificity. The rate of positive hair samples for excessive drinking was 33.3% (32.4% among women and 35.4% among men) (n = 324). The majority of samples (62%) had cumulative FAEE levels above a level that excludes strict abstinence (0.2 ng/mg) and many (19%) were highly positive (above 1.0 ng/mg). Of 26 FAEE hair tests for which women were reported to be pregnant, 38% had FAEE hair levels above 0.2 ng/mg and 19% tested positive for excessive drinking, with levels above 0.5 ng/mg; 12% had levels above 1.0 ng/mg. The high rate of positive FAEE results demonstrates that the FAEE hair test corroborates the clinical suspicion of alcohol use in parents of children at risk for FASD. Our results suggest that FAEE hair analysis may be a powerful tool in detecting excessive alcohol use in the perinatal period.

Simultaneous quantification of linezolid, rifampicin, levofloxacin, and moxifloxacin in human plasma using high-performance liquid chromatography with UV.

Abstract: :A high-performance liquid chromatography method with UV detection was developed and validated for the simultaneous quantification of linezolid (LZD), rifampicin (RFP), levofloxacin (LEVO), and moxifloxacin (MOXI) in human plasma. The method is based on a simple organic protein precipitation

Multicenter evaluation of a novel nanoparticle immunoassay for 5-fluorouracil on the Olympus AU400 analyzer.

Abstract: Background:5-Fluorouracil (5-FU) is the most widely used chemotherapy drug, primarily against gastrointestinal, head and neck, and breast cancers. 5-FU has large pharmacokinetic variability resulting in unexpected toxicity or ineffective treatment. Therapeutic drug management of 5-FU minimizes toxic

Falsely increased blood tacrolimus concentrations using the ACMIA assay due to circulating endogenous antibodies in a liver transplant recipient: a tentative approach to obtaining reliable results.

Abstract: The presence of endogenous antibodies in the serum of some patients has long been known to be a potential source of interference in immunoassays. We report falsely increased whole blood tacrolimus concentrations using the antibody conjugated magnetic immunoassay from Siemens HealthCare Diagnostics in a liver transplant recipient due to the presence of circulating endogenous antibodies (possibly heterophilic antibodies). Estimation of whole blood tacrolimus concentrations from the washed erythrocytes concentrations is proposed as a tentative approach for obtaining reliable results using the antibody conjugated magnetic immunoassay assay in these cases, leading to analogous blood tacrolimus concentrations to those produced by the microparticle enzyme immunoassay from Abbott Laboratories.

Population pharmacokinetics of tacrolimus in pediatric hematopoietic stem cell transplant recipients: new initial dosage suggestions and a model-based dosage adjustment tool.

Abstract: The population pharmacokinetics of tacrolimus was described in 22 paediatric haematopoietic stem cell transplant recipients and a model-based dosage adjustment tool that may assist with therapy in ...

Effect of valproate on olanzapine plasma concentrations in patients with bipolar or schizoaffective disorder.

Abstract: The effect of valproate on the steady-state plasma concentrations of olanzapine was investigated in 18 patients with bipolar or schizoaffective disorder. Additional valproate, at a dose ranging from 600 to 2000 mg/d, was administered for 4 weeks to patients stabilized on olanzapine (5-20 mg/d). During valproate coadministration, mean plasma olanzapine concentrations decreased significantly from 32.9 +/- 9.7 ng/mL at baseline to 27.4 +/- 9.8 ng/mL at week 2 (P = 0.02), and to 26.9 +/- 9.2 ng/mL at week 4 (P = 0.001). Smoking also decreased plasma olanzapine concentrations. Valproate coadministration with olanzapine was well tolerated and no patient showed a worsening of his or her psychopathological condition. These findings indicate that valproate, at doses of up to 2000 mg/d, is associated with a minimal, presumably not clinically significant, decrease in plasma olanzapine concentrations, possibly as a result of induction of olanzapine metabolism. New studies are needed to confirm that valproate could have mild inductive effects.

Simultaneous quantification of erlotinib, gefitinib, and imatinib in human plasma by liquid chromatography tandem mass spectrometry.

Abstract: A quantitative liquid chromatography (LC)-mass spectrometry (MS)/MS method in human plasma was developed and validated for the tyrosine kinase inhibitors erlotinib, gefitinib, and imatinib in human plasma. Pre-treatment of the samples was achieved by using liquid-liquid extraction using D-8 imatinib as internal standard. Separation was performed on a Waters Alliance 2795 LC system using an XBridge RP18 column. The mass spectrometer Micromass was equipped with an electro spray ionization probe, operating in the positive mode. The calibration curves in plasma were linear for erlotinib, gefitinib, and imatinib over the concentration range of 5 to 3,000; 5 to 3,000, and 5 to 5,000 ng/mL, respectively. The intraday and interday accuracy ranged from 90% to 110% and the intraday and interday precision of the method was within 5%. The reported method provided the necessary linearity, precision, and accuracy to determine tyrosine kinase inhibitors in clinical research and for therapeutic drug monitoring.

LC-MS/MS extends the range of drug analysis in pain patients.

Abstract: The current study addresses the distribution of low concentrations of excreted drugs in the pain patient population in an effort to establish a more rational set of cutoffs for this cohort. To wit, 19 analytes in approximately 8000 urine specimens from pain patients were measured using liquid chromatography tandem mass spectroscopy (LC-MS/MS) methodology. The lower limits of quantitation for the LC-MS/MS were set as the nominal cutoffs for the determination of positive and negative results. The measured concentrations were compared with the Substance Abuse & Mental Health Services Administration (SAMHSA) nominal immunoassay cutoffs, and a subset of "missed samples" was identified for each of the 19 analytes. This "missed samples" subset contained all samples that measured above the LC MS/MS cutoff for a given analyte but below the SAMHSA immunoassay cutoff. The number of "missed samples" divided by the total number of samples measured positive by the LC-MS/MS method defines the percentage of this population that would have been found falsely negative if a prescreen by immunoassay using SAMHSA cutoffs had been conducted. For example, 69% of the specimens that were positive for hydromorphone by LC-MS/MS would have been falsely scored as negative by immunoassay.

Unsuspected exposure to cocaine in preschool children from a Mediterranean city detected by hair analysis.

Abstract: We used hair testing to investigate the prevalence of unsuspected exposure to cocaine in a group of preschool children presenting to an urban pediatric emergency department without signs or symptoms suggestive of exposure. Hair samples were obtained from 90 children between 18 months and 5 years of age attending the emergency room of Hospital del Mar in Barcelona, Spain. In 85 cases, hair samples from the accompanying parent were also provided. The samples were analyzed for the presence of cocaine and benzoylecgonine by gas chromatography-mass spectrometry, which also determined opiates and amphetamines. Parental sociodemographics, possible drug history, and information on the child's features were recorded. Hair samples from 21 children (23.3%) were positive for cocaine (concentration range 0.3-5.96 ng/mg of hair) with 1 sample also positive for 3,4-methylenedioxymethamphetamine and another for opiates. In 88% of the positive cases, cocaine was also found in the hair of the accompanying parent (15 of 17 matched parent-child hair samples). Parental sociodemographics were associated neither with children's exposure to cocaine nor with somatometry of children at birth. However, the behavioral patterns with potential harmful effects for the child's health (eg, tobacco smoking, cannabis, benzodiazepines and/or antidepressants use, and shorter breast-feeding time) were significantly higher in the parents of exposed children. A statistically higher percentage of exposed children were in the lower weight percentile group compared with the nonexposed children. In the light of these results, we advocate general hair screening to disclose exposure to cocaine and other drugs of abuse in children from risky environments, which could provide the basis for specific social and health interventions.