Abraham J. Wilhelm

Therapeutic Drug Monitoring by Dried Blood Spot: Progress to Date and Future Directions

This article discusses dried blood spot (DBS) sampling in therapeutic drug monitoring (TDM). The most important advantages of DBS sampling in TDM are the minimally invasive procedure of a finger prick (home sampling), the small volume (children), and the stability of the analyte. Many assays in DBS have been reported in the literature over the previous 5 years. These assays and their analytical techniques are reviewed here. Factors that may influence the accuracy and reproducibility of DBS methods are also discussed. Important issues are the correlation with plasma/serum concentrations and the influence of hematocrit on spot size and recovery. The different substrate materials are considered. DBS sampling can be a valid alternative to conventional venous sampling. However, patient correlation studies are indispensable to prove this. Promising developments are dried plasma spots using membrane and hematocrit correction using the potassium concentration.

Analysis of cyclosporin A in dried blood spots using liquid chromatography tandem mass spectrometry

Dried blood spot sampling is a promising and patient friendly alternative for venous sampling. A liquid chromatography tandem mass spectrometer assay was developed for analyzing cyclosporin A in dried blood spots. Linearity ranged from 25 to 1440 microg/L. Within and between run accuracy and precision were within limits. The developed assay has a negligible matrix-effect and a recovery of 97%. The dried blood spots were stable during a period of at least 17 days in the refrigerator. The developed assay is suitable for analyzing cyclosporin A in dried blood spots.

Boron Neutron Capture Therapy for Glioblastoma Multiforme

Aim: Glioblastoma multiforme (GBM) is an incurable disease that can only be managed in a palliative way. The GBM accounts for approximately half of all newly diagnosed primary brain tumors with an incidence of 2–3 cases per 100,000 people each year. Surgery and radiation are the standard options for palliation, and whether there is a place for chemotherapy is still discussed. Boron neutron capture therapy (BNCT) is a promising and possibly curative method of treating GBM. The purpose of this article is to provide an updated review on the current management and future possibilities of treating GBM with BNCT.Method: Use was made of computerized searches and of checking cross-references of articles and book chapters.Results: The principle of BNCT uses the high ability of 10B to capture thermal neutrons and to disintegrate immediately into a He nucleus (α-particle) and a Li nucleus. To reach a sufficient concentration of 10B in the malignant cells compared to the surrounding healthy tissue, 10B-carriers must be highly tumor-selective. At present, the 10B carriers boronophenylalanine (BPA) and sodium borocaptate (BSH) are used in clinical trials to perform BNCT.Conclusion: The BNCT is a promising and possibly curative method of treating GBM, but at present this procedure is far from perfect. Because of the lack of selectivity of the boron carriers, it appears so far that radiation toxicity limits the radiation dose, so that tumor damage is modest. Current investigations and developments are aimed at targeting the boron carriers to the tumor, in order to limit the damage to the healthy, surrounding tissue.

Simultaneous Quantification of Erlotinib, Gefitinib, and Imatinib in Human Plasma by Liquid Chromatography Tandem Mass Spectrometry

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.

Analysis of mycophenolic acid in dried blood spots using reversed phase high performance liquid chromatography

At our laboratory a reversed phase high performance liquid chromatography assay was developed for analysis of mycophenolic acid in dried blood spot samples. The assay was validated in the range of 0.74-23.4mg/L and proved to be accurate and precise. The developed sample pretreatment procedure was consistent and has a recovery of 95.2% for mycophenolic acid. Hematocrit showed to have influence on the physics of the blood spots and thus on the concentration of mycophenolic acid, therefore standard and control samples should be made with a standardized hematocrit.

Clinical validation of dried blood spot sampling in therapeutic drug monitoring of ciclosporin A in allogeneic stem cell transplant recipients: direct comparison between capillary and venous sampling.

Background:The immunosuppressive drug ciclosporin A has a narrow therapeutic window and a large inter- and intraindividual pharmacokinetic variability. Therapeutic drug monitoring of ciclosporin is usually performed in ethylenediaminetetraacetic acid blood, obtained by venous sampling. Dried blood spot sampling (DBS) could be a useful alternative sampling method, which also easily allows multiple sampling, for example, for obtaining area under the curve. With DBS, capillary blood is obtained from a finger prick with an automatic lancet by the patients themselves, and the drop of blood is applied to sampling paper. This may limit the number and duration of hospital visits for these patients. Methods:We describe a validation study in which venous and finger prick blood samples were collected at the same time. Venous sampling was performed by venipuncture, and the ethylenediaminetetraacetic acid blood samples were collected and stored at 4°C until analysis. Finger prick blood samples were collected using an automatic lancing device. The volume of the blood drops of patients was approximately 30 &mgr;L, and blood spots of about 10-mm diameter were produced. Paper disks with a diameter of 8 mm were punched out with an electromagnetic-driven hole puncher. DBS was compared with the routine assay in venous blood. The study population consisted of adult patients (18 years or older) who were treated with ciclosporin A and routinely monitored for adequate blood concentrations. Results:Thirty-eight duplicate dried blood spots and venous samples were studied. Using weighted Deming regression, the slope was 1.01 with a standard error of 0.03 associated with an intercept of −9.0 (standard error = 5.9). These results indicate that there is no significant difference between the 2 sampling methods. For the medical decision level of 300 mcg/L, the bias was −4.7 mcg/L with a 95% confidence interval of −19.2 to 9.8 mcg/L. The Altman–Bland plot showed no difference between the 2 sampling methods. Conclusions:Our results demonstrate that DBS is a valid alternative for conventional venous sampling in allogeneic stem cell transplant recipients.

Toxicokinetics of nortriptyline and amitriptyline: two case reports.

Two cases are presented of intentional intoxications with the tricyclic antidepressants (TCAs) nortriptyline (NT) and amitriptyline (AT). The peak plasma concentrations were 2290 &mgr;g/L and 2900 &mgr;g/L, respectively. The active metabolites E-10-hydroxynortriptyline (EHNT) and Z-10-hydroxynortriptyline (ZHNT) profiles were quite different as monitored for 5 to 10 days after presumed drug intake. In conclusion, these cases illustrate that (1) metabolite formation and elimination after intake of an overdose dose of NT and AT are stereoselective, and (2) NT and EHNT toxicokinetics and toxicodynamics are quite different. It also shows that a patient with a severe TCA overdose can still survive if he or she receives appropriate and quick supportive care, even if the prognostic markers QRS time, coma grade, and serum TCA levels predict poor outcome.

Rapid quantification of gabapentin, pregabalin, and vigabatrin in human serum by ultraperformance liquid chromatography with mass-spectrometric detection.

Background:Gabapentin (GBP), pregabalin (PRG), and vigabatrin (VIG) are used for the prevention and treatment of epileptic seizures. The developed method was applied to samples from subjects participating in a pharmacokinetic study of GBP. Methods:Sample pretreatment consisted of adding 20 &mgr;L of trichloroacetic acid (30%; vol/vol) and 200 &mgr;L of GBP-d4 in acetonitrile as an internal standard to 20 &mgr;L of serum. Chromatographic separation was performed on an Acquity separation module using a Kinetex RP18 column. The aqueous and organic mobile phases were 2 mM ammonium acetate supplemented with 0.1% formic acid in water and acetonitrile, respectively. The detection by a tandem quadrupole mass spectrometer, operating in the positive mode using multiple reaction monitoring, was completed within 2 minutes. Results:The method was linear over the range of 0.03–25 mg/L for GBP, 0.03–25 mg/L for PRG, and 0.06–50 mg/L for VIG. The between- and within-run accuracies ranged from 90% to 107%. The between- and within-run imprecisions of the method were <10%. Stability data show no significant decrease of the analytes. A relative matrix effect of −1%, 0.2%, and −5% was determined for GBP, PRG, and VIG, respectively. Conclusions:A simple and sensitive ultraperformance liquid chromatography–tandem mass spectrometry method was developed and validated for the simultaneous quantification of GBP, PRG, and VIG in human serum. The reported method provided the necessary linearity, precision, and accuracy to allow the determination of GBP, PRG, and VIG for therapeutic drug monitoring and clinical research purposes.

Validated Liquid Chromatography-Tandem Mass Spectroscopy Method for the Simultaneous Quantification of Four Antimycotic Agents in Human Serum

A liquid chromatography-tandem mass spectrometry method was developed and validated for the simultaneous quantification of voriconazole, fluconazole, posaconazole, itraconazole, and hydroxyitraconazole in human serum. A simple protein precipitation was used as sample pretreatment with ketoconazole as the internal standard. Chromatographic separation was performed on a Waters Alliance 2795 liquid chromatography system using a XBridge RP18 column. The mass spectrometer from Micromass was equipped with an electrospray ionization probe operating in the positive mode using multiple reaction monitoring. The method was linear over the range of 0.01 to 5.00 mg/L for itraconazole, 0.01 to 5.00 mg/L for OH-itraconazole, 0.02 to 10.00 mg/L for voriconazole, 0.06 to 30.00 mg/L for fluconazol, and 0.02 to 10.00 mg/L for posaconazole. The between- and within-run accuracy ranged from 92% to 110%. The between- and within-run imprecision of the method was less than 11%. The reported method provided the necessary linearity, precision, and accuracy to allow the determination of four antimycotic agents for therapeutic drug monitoring and pharmacokinetic-pharmacodynamic studies.

Stability of monoHER in an aqueous formulation for i.v. administration.

MonoHER is a semisynthetic flavonoid used successfully in modulating the cardiotoxic effect of doxorubicin but not its antitumor activity. The oral bioavailability of monoHER is <1%. Therefore, it should be prepared as an i.v. formulation for use in clinical trials. The solubility of monoHER in water is highly pH dependent. At pH</=8.3 the drug precipitates 4 h after preparation. DMSO was tested for enhancing the solubility of monoHER in aqueous solutions. In all DMSO-based aqueous solutions monoHER recrystalized again at pH<8.3 and room temperature within 4 h after preparation. Moreover, the stability of monoHER was lower in a DMSO stock solution than after dilution with an aqueous solution. The stability of monoHER was tested in alkaline solutions (pH 8.3 and 9.5) using an HPLC-DAD procedure to detect all possible degradation products within 10 min after injection. Minor degradation occurred to monoHER in alkaline solutions when exposed to daylight or 1% H(2)O(2). MonoHER intensively degraded when exposed to a high temperature (80 degrees C). The stability of monoHER was almost the same in saline or 5% glucose when kept at room temperature and an alkaline pH of 8.3 and 9.5. Under shelf-life conditions the stability of monoHER in 5% glucose (pH 8.4), decreased with about 10% during 48 h after preparation.