Jan-Willem C. Alffenaar

Clinical Relevance of the Pharmacokinetic Interactions of Azole Antifungal Drugs with Other Coadministered Agents

There are currently a number of licensed azole antifungal drugs; however; only 4 (namely, fluconazole, itraconazole, posaconazole, and voriconazole) are used frequently in a clinical setting for prophylaxis or treatment of systemic fungal infections. In this article, we review the pharmacokinetic interactions of these azole antifungal drugs with other coadministered agents. We describe these (2-way) interactions and the extent to which metabolic pathways and/or other supposed mechanisms are involved in these interactions. This article provides an overview of all published drug-drug interactions in humans (either healthy volunteers or patients), and on the basis of these findings, we have developed recommendations for managing the specific interactions.

Management of patients with multidrug-resistant/extensively drug-resistant tuberculosis in Europe: a TBNET consensus statement

The emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) substantially challenges TB control, especially in the European Region of the World Health Organization, where the highest prevalence of MDR/XDR cases is reported. The current management of patients with MDR/XDR-TB is extremely complex for medical, social and public health systems. The treatment with currently available anti-TB therapies to achieve relapse-free cure is long and undermined by a high frequency of adverse drug events, suboptimal treatment adherence, high costs and low treatment success rates. Availability of optimal management for patients with MDR/XDR-TB is limited even in the European Region. In the absence of a preventive vaccine, more effective diagnostic tools and novel therapeutic interventions the control of MDR/XDR-TB will be extremely difficult. Despite recent scientific advances in MDR/XDR-TB care, decisions for the management of patients with MDR/XDR-TB and their contacts often rely on expert opinions, rather than on clinical evidence. This document summarises the current knowledge on the prevention, diagnosis and treatment of adults and children with MDR/XDR-TB and their contacts, and provides expert consensus recommendations on questions where scientific evidence is still lacking. TBNET consensus statement on the management of patients with MDR/XDR-TB has been released in the Eur Respir J http://ow.ly/uizRD

Determination of moxifloxacin in dried blood spots using LC-MS/MS and the impact of the hematocrit and blood volume.

Moxifloxacin (MFX) is a potential oral agent use in the treatment of multidrug-resistance tuberculosis (MDR-TB). Due to variability in pharmacokinetics and in vitro susceptibility of causative bacteria, therapeutic drug monitoring (TDM) of MFX is recommended. Conventional plasma sampling for TDM is facing logistical challenges, especially in limited resource areas, and dried blood spots (DBS) sampling may offer a chance to overcome this problem. The objective of this study was to develop a LC-MS/MS method for determination of MFX in dried blood spots (DBS) that is applicable for TDM. The influence of paper type, the hematocrit (Hct) and the blood volume per spot (V(b)) on the estimated blood volume in a disc (V(est)) was investigated. The extracts of 8mm diameter discs punched out from DBS were analyzed using liquid chromatography tandem mass spectrometry (LC-MS/MS) with cyanoimipramin as internal standard. The method was validated with respect to selectivity, linearity, accuracy, precision, sensitivity, recovery and stability. The effect of Hct and V(b) on LC-MS/MS analytical result was also investigated. The relationship between MFX concentrations in venous and finger prick DBS and those in plasma was clinically explored. V(est) was highly influenced by Hct while the effect of V(b) appeared to be different among paper types. Calibration curves were linear in the range of 0.05-6.00 mg/L with inter-day and intra-day precisions and biases of less than 11.1%. The recovery was 84.5, 85.1 and 92.6% in response to blood concentration of 0.15, 2.50 and 5.00 mg/L, respectively. A matrix effect of less than 11.9% was observed. MFX in DBS was stable for at least 4 weeks at room condition (temperature of 25°C and humidity of 50%). A large range of Hct value produced a significant analytical bias and it can be corrected with resulting DBS size. A good correlation between DBS and plasma concentrations was observed and comparable results between venous DBS and finger prick DBS was attained. This fully validated method is suitable for determination of MFX in dried blood spot and applicable for TDM.

Method for therapeutic drug monitoring of azole antifungal drugs in human serum using LC/MS/MS

Fungal infections occur in immunocompromised patients. Azole antifungal agents are used for the prophylaxis and treatment of these infections. The interest in therapeutic drug monitoring azole agents has increased over the last few years. Inter- and intra-patient variability of pharmacokinetics, drug-drug interactions, serum concentration related toxicity and success of therapy has stressed the need of frequently therapeutic drug monitoring of the drugs, belonging to the group of azoles. Therefore a simple, rapid and flexible method of analysis is required. This method is based on the precipitation of proteins in human serum with LC/MS/MS detection. Validation was performed according to the guidelines for bioanalytical method validation of the food and drug administration agency. The four most used azole drugs can be detected in human serum within the clinical relevant serum levels with good accuracy and reproducibility at the limit of quantification. Intra- and inter-day validation demonstrated good accuracy and reproducibility. A rapid, sensitive and flexible LC/MS/MS method has been developed and validated to measure voriconazole (VRZ), fluconazole (FLZ), itraconazole (ITZ) and posaconazole (PSZ) in human serum. This new method is suitable for clinical pharmacokinetic studies and routine monitoring in daily practice.

Fast LC-MS/MS analysis of tacrolimus, sirolimus, everolimus and cyclosporin A in dried blood spots and the influence of the hematocrit and immunosuppressant concentration on recovery

We developed a method for the analysis of four immunosuppressants in dried blood spot (DBS) samples to facilitate therapeutic drug monitoring for transplant patients outside the hospital. An 8mm disc from the central part of the DBS was punched, extracted and followed by LC-MS/MS analysis. The method was validated with ranges from 1.00-50.0 µg/L for tacrolimus, sirolimus and everolimus, and from 20.0-2000 µg/L for cyclosporin A. The validation showed a maximum overall bias of 13.0% for the sirolimus LLOQ, while the maximum overall CV was 15.7% for the everolimus LLOQ. All four immunosuppressants showed to be stable in DBS for at least 7 days at 22°C. The volume of the blood spot showed to have minor effect on measured concentrations. A cross-validation test between the 31 ET CHR paper and the Whatman FTA DMPK-C cards showed no significant difference between the two types of paper. During validation the hematocrit (HT) showed to have significant influence on the analytical results. When the measured concentrations were corrected for the effect of the HT, biases improved significantly. Additional recovery tests proved that the combination of especially low HT and high concentration does not only affect the spot size but can also affect the extraction recoveries of sirolimus and especially everolimus. Although the tested parameters like HT and concentrations are extreme and unlikely for routine analysis of outpatients, the fundamental effect of the combination of these parameters on extraction recoveries are proven with this research. The protein binding in the blood and hydrogen binding to the cellulose of the paper is suggested to influence extractions and gives new insights in the extraction methodology of DBS samples. The observed HT effect during the validation appeared to be negligible during the correlation study as no concentration corrections for the HT values were needed. Nevertheless, results from DBS samples with extremely high concentrations combined with extremely low HT values should be interpreted with caution. The patient correlation study showed good correlations with R(2) values higher than 0.87 between venous whole blood and venous DBS samples were observed for all four immunosuppressants. The Passing & Bablok plots showed positive biases of the slopes of 18% for tacrolimus and less than 12% for sirolimus, everolimus and cyclosporin A. The validated method, proved stability of the immunosuppressants in DBS, and the correlation study showed the capability of the DBS method to be used as an alternative for whole blood analysis in therapeutic drug monitoring.

Daily 300 mg dose of linezolid for multidrug-resistant and extensively drug-resistant tuberculosis: updated analysis of 51 patients

Conclusions: Our findings suggest that linezolid at a daily dose of 300 mg is effective against intractable MDR/XDR-TB, and may be associated with fewer neuropathic side effects than a daily dose of 600 or 1200 mg.

Pharmacokinetics of Moxifloxacin in Cerebrospinal Fluid and Plasma in Patients with Tuberculous Meningitis

Moxifloxacin cerebrospinal fluid (CSF) penetration was evaluated by obtaining full plasma and CSF time concentration curves for 4 patients with tuberculous meningitis. The geometric mean ratio of the areas under the curve for CSF to plasma were 0.82 (range, 0.70-0.94) at 400 mg once per day and 0.71 (0.58-0.84) at 800 mg once per day.

Effectiveness and safety of meropenem/ clavulanate-containing regimens in the treatment of MDR- and XDR-TB

No large study has ever evaluated the efficacy, safety and tolerability of meropenem/clavulanate to treat multidrug- and extensively drug-resistant tuberculosis (MDR- and XDR-TB). The aim of this observational study was to evaluate the therapeutic contribution, effectiveness, safety and tolerability profile of meropenem/clavulanate added to a background regimen when treating MDR- and XDR-TB cases. Patients treated with a meropenem/clavulanate-containing regimen (n=96) showed a greater drug resistance profile than those exposed to a meropenem/clavulanate-sparing regimen (n=168): in the former group XDR-TB was more frequent (49% versus 6.0%, p<0.0001) and the median (interquartile range (IQR)) number of antibiotic resistances was higher (8 (6–9) versus 5 (4–6)). Patients were treated with a meropenem/clavulanate-containing regimen for a median (IQR) of 85 (49–156) days. No statistically significant differences were observed in the overall MDR-TB cohort and in the subgroups with and without the XDR-TB patients; in particular, sputum smear and culture conversion rates were similar in XDR-TB patients exposed to meropenem/clavulanate-containing regimens (88.0% versus 100.0%, p=1.00 and 88.0% versus 100.0%, p=1.00, respectively). Only six cases reported adverse events attributable to meropenem/clavulanate (four of them then restarting treatment). The nondifferent outcomes and bacteriological conversion rate observed in cases who were more severe than controls might imply that meropenem/clavulanate could be active in treating MDR- and XDR-TB cases. Meropenem/clavulanate is effective and safe to treat MDR- and XDR-TB in comparison with controls http://ow.ly/XG75j

Dried Blood Spot Analysis for Therapeutic Drug Monitoring of Linezolid in Patients with Multidrug-Resistant Tuberculosis

ABSTRACT Linezolid is a promising antimicrobial agent for the treatment of multidrug-resistant tuberculosis (MDR-TB), but its use is limited by toxicity. Therapeutic drug monitoring (TDM) may help to minimize toxicity while adequate drug exposure is maintained. Conventional plasma sampling and monitoring might be hindered in many parts of the world by logistical problems that may be solved by dried blood spot (DBS) sampling. The aim of this study was to develop and validate a novel method for TDM of linezolid in MDR-TB patients using DBS sampling. Plasma, venous DBS, and capillary DBS specimens were obtained simultaneously from eight patients receiving linezolid. A DBS sampling method was developed and clinically validated by comparing DBS with plasma results using Passing-Bablok regression and Bland-Altman analysis. This study showed that DBS analysis was reproducible and robust. Accuracy and between- and within-day precision values from three validations presented as bias and coefficient of variation (CV) were less than 17.2% for the lower limit of quantification and less than 7.8% for other levels. The method showed a high recovery of approximately 95% and a low matrix effect of less than 8.7%. DBS specimens were stable at 37°C for 2 months and at 50°C for 1 week. The ratio of the concentration of linezolid in DBS samples to that in plasma was 1.2 (95% confidence interval [CI], 1.12 to 1.27). Linezolid exposure calculated from concentrations DBS samples and plasma showed good agreement. In conclusion, DBS analysis of linezolid is a promising tool to optimize linezolid treatment in MDR-TB patients. An easy sampling procedure and high sample stability may facilitate TDM, even in underdeveloped countries with limited resources and where conventional plasma sampling is not feasible.

Evaluation of moxifloxacin for the treatment of tuberculosis : 3 years of experience

Moxifloxacin (MFX) is a powerful second-line anti-tuberculosis (TB) agent, but the optimal dose has not yet been established and long-term safety data are scarce. We retrospectively reviewed the medical charts of TB patients treated at the Tuberculosis Centre Beatrixoord, University Medical Centre Groningen (Haren, the Netherlands) receiving MFX 400 mg once daily as part of their TB treatment between January 1 2006 and January 1 2009. Safety data and drug–drug interactions were evaluated. Efficacy was predicted based on the area under the concentration–time curve up to 24 h post-dosage (AUC0–24h)/minimal inhibitory concentration (MIC) ratio. 89 patients were treated with a median dose of 6.9 mg·kg−1 MFX once daily for a median period of 74 days. Discontinuation of therapy occurred in only three patients due to gastrointestinal side-effects and hypersensitivity. Pharmacokinetic analysis showed an AUC0–24h/MIC ratio <100 in eight out of 16 patients. A large variation in protein binding affected the unbound AUC0–24h considerably. These data show that MFX treatment was well tolerated in 89 patients receiving a dose of 400 mg once daily for a prolonged period. Considering the variability in (un)bound AUC0–24h/MIC ratio, therapeutic drug monitoring is recommended in selected patients (i.e. rifampicin co-medication; MIC ≥0.25 mg·L−1) to assess optimal therapy.