M. P. H. van den Broek

Easy and fast LC-MS/MS determination of lidocaine and MEGX in plasma for therapeutic drug monitoring in neonates with seizures.

A fast liquid chromatography-tandem mass spectrometry with electrospray ionization method was developed and validated for simultaneous quantification of lidocaine and its active metabolite MEGX in 10 μL of plasma of neonates with seizures. The sample preparation consists of an easy protein precipitation sample pre-treatment with methanol. Chromatographic separation was achieved on a Alltima HP C18-EPS 150 mm×2.1mm column with an isocratic mobile phase of 0.1% (v/v) ammonium acetate in purified water-0.1% (v/v) formic acid in acetonitrile (70:30, v/v). The analytes were detected with a Thermo Scientific triple quadrupole Quantum Access with positive ionization. Ions monitored in the selected reaction monitoring (SRM) mode were m/z 235.2→86.6 for lidocaine (at 3.35 min), m/z 207.1→58.8 for MEGX (at 2.75 min) and 280.1→86.7 for 3-nitrolidocaine (internal standard, at 3.20 min). The method was validated over a linear range of 0.2-18.0mg/L for lidocaine and MEGX, using 3-nitrolidocaine as the internal standard. The lower limit of quantification (LLQ) was 0.2mg/L for lidocaine and MEGX. The within-run and between-run CV (%) were lower than 6.9% for both lidocaine and MEGX. Recoveries were in the range of 99.4% to 103.6%. Observed LC-MS/MS matrix effects were -6.2% for MEGX (ion suppression) and were negligible for lidocaine and the internal standard (i.e. <0.1%). Compared to other bioanalytical articles published in medical literature (PubMed) during the last 15 years that described LC-MS/MS methods for quantification of lidocaine in human plasma, our method uses less plasma, has a shorter and more simple sample pre-treatment and has a short run time.

Quantitative determination of oseltamivir and oseltamivir carboxylate in human fluoride EDTA plasma including the ex vivo stability using high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry

Oseltamivir, the ethyl ester prodrug of the neuramidase inhibitor oseltamivir carboxylate, is licensed for the treatment of patients with influenza virus infection. Here we describe the development and validation of an assay for the simultaneous quantification of oseltamivir and oseltamivir carboxylate in human fluoride EDTA plasma including the ex vivo stability using liquid chromatography coupled to tandem mass spectrometry. Sample pretreatment consisted of protein precipitation with 8% (v/v) trichloroacetic acid in water using only 50 μL plasma. Chromatographic separation was performed on a reversed phase C18 column (150 mm × 2.0 mm ID, particle size 4 μm) with a stepwise gradient using 0.1% formic acid and methanol at a flow rate of 250 μL/min. A triple quadrupole mass spectrometer operating in the positive ionization mode was used for detection and drug quantification. The method was validated over a range of 3-300 ng/mL for oseltamivir and 10-10,000 ng/mL for oseltamivir carboxylate. Deuterated oseltamivir and oseltamivir carboxylate were used as internal standards. The intra-assay accuracies and precisions for oseltamivir were between -8.8 and 16.3% at the LLOQ level, whereas for all other concentration levels this was -8.6 and 14.5%. For oseltamivir carboxylate the intra-assay accuracies and precisions were between -10.9 and 10.7% at all levels. Furthermore, oseltamivir was stable in plasma and whole blood ex vivo in commercially available fluoride EDTA tubes for at least 24h at 2-8 °C. This method is now applied for the determination of both compounds in specific patient populations to evaluate current dosing guidelines.

Epidemiology, pathophysiology and putative genetic basis of carbamazepine- and oxcarbazepine-induced hyponatremia

The use of carbamazepine (CBZ) and oxcarbazepine (OXC) as first‐line antiepileptic drugs in the treatment of focal epilepsy is limited by hyponatremia, a known adverse effect. Hyponatremia occurs in up to half of people taking CBZ or OXC and, although often assumed to be asymptomatic, it can lead to symptoms ranging from unsteadiness and mild confusion to seizures and coma. Hyponatremia is probably due to the antidiuretic properties of CBZ and OXC that are, at least partly, explained by stimulation of the vasopressin 2 receptor/aquaporin 2 pathway. No known genetic risk variants for CBZ‐ and OXC‐induced hyponatremia exist, but likely candidate genes are part of the vasopressin water reabsorption pathway.

Pregnancy and fetal outcomes after paternal exposure to azathioprine, methotrexate or mycophenolic acid: a critically appraised topic

A 35-year-old male patient with atopic dermatitis (AD) is being treated with mycophenolate mofetil (MMF). He and his female partner wish to have children. They wonder whether the use of MMF, or any of the other alternative oral immunosuppressive drugs to treat AD, will be a risk for the fetus and whether this medication should be discontinued. He searched on the internet and found that the use of MMF was contraindicated.

Pharmacokinetics of oseltamivir carboxylate in critically ill patients : each patient is unique

Dear Editor, Patients infected with the 2009 H1N1 pandemic influenza virus often develop severe viral pneumonia with acute respiratory distress syndrome (ARDS) and multiple organ failure. High-dose oseltamivir (C150 mg twice daily) has been advocated as optimal treatment [1]. However, the scientific evidence for this advice is lacking thus far [2]. Therefore, we explored the pharmacokinetics of oseltamivir and its active metabolite oseltamivir carboxylate in critically ill patients with H1N1 pandemic influenza following different dosing regimens. All patients with H1N1 pandemic influenza admitted to the ICU of the University Medical Center Utrecht were eligible for inclusion. Patients received oseltamivir at a dose determined by their treating physician, and blood samples were drawn at t = 0, 1, 2, 3, 4 and 8 h on day three of treatment. Oseltamivir and oseltamivir carboxylate plasma concentrations were determined by HPLC–MS/MS [3]. The area under the concentration–time curve from 0 to 8 h (AUC0–8) was estimated using noncompartmental analysis. Patient characteristics were obtained from the patient files. Six patients were included in the analysis (Table 1). All patients had ARDS due to H1N1 pneumonitis. Additionally, patient 1 had a pulmonary embolism, patient 2 had kidney failure caused by multiple renal cysts and received continuous venovenous hemofiltration (CVVH; blood flow 200 mL/min, ultrafiltrate flow 2 L/h), patient 3 had received stem cell transplantation and suffered from pulmonary aspergillosis, patient 4 was 29 weeks pregnant (a cesarean section was performed a few hours before sampling), patient 5 was on extracorporeal membrane oxygenation, and patient 6 had newly diagnosed hairy cell leukemia and renal failure for which CVVH was started the day after sampling. The pharmacokinetic parameters, as well as the prescribed dose, were widely variable (Table 1). No relationship was observed between dose and AUC0–8. Thus far, no concentration– response relationship has been established for oseltamivir. However, a carboxylate AUC of[2,270 ng h/mL is considered adequate [4]. Despite a high variability, all carboxylate AUC0–8 in this study were [2,270 ng h/mL. In line with

Predicting therapy response to mycophenolic acid using UGT1A9 genotyping: towards personalized medicine in atopic dermatitis

Abstract Atopic dermatitis (AD) is a very common chronic inflammatory skin disease requiring long-term treatment. Mycophenolic acid (MPA) is used off-label in treatment of patients with severe AD failing Cyclosporin A (CsA) treatment, however clinical efficacy is observed in only half of the AD patients. In blood, MPA levels are known to have a large interindividual variability. Low MPA exposure and increased enzyme activity correlates with the presence of UGT1A9 polymorphisms. In this retrospective study, 65 adult AD patients treated with MPA were classified as responder or non-responder to MPA treatment. UGT1A9 polymorphisms were determined using PCR. A significantly higher number of UGT1A9 polymorphisms was found in the group that did not respond to MPA treatment. Of the patients that carried a UGT1A9 polymorphism, 85.7% were non-responsive to MPA treatment. This implies that non-responsiveness in AD patients is more likely to occur in carriers of a UGT1A9 polymorphism. In a binary logistic regression analysis the odds ratio (OR) was 8.65 (95% confidence interval: 0.93–80.17). Our results show that UGT1A9 polymorphisms can be used to identify patients with non-responsiveness to MPA. Patients with UGT1A9 polymorphisms might benefit from higher MPA dosage.

Use of oral immunosuppressive drugs in the treatment of atopic dermatitis in the Netherlands

Although atopic dermatitis (AD) is a very common skin disease, data on the percentage of patients with really difficult‐to‐treat AD are scarce. From socio‐economic perspective, it is important to have more insight into these numbers, as new very effective, but expensive, treatment options will be available in the near future for difficult‐to‐treat AD. Estimating the number of patients with AD using oral immunosuppressive drugs can give an impression of the percentage of difficult‐to‐treat patients in the total AD population.

Thiopurine metabolite levels in patients with atopic dermatitis and/or chronic hand/foot eczema treated with azathioprine

Abstract Background: Azathioprine is frequently used in severe eczema. It is converted in the liver into active metabolites, including 6-thioguanine nucleotide (6-TGN) and methylated 6-methylmercaptopurine (6-MMP). In the past, the therapeutic potential of azathioprine may have not been fully utilized. Recent investigations on inflammatory bowel disease have led to a better understanding of azathioprine metabolism and optimizing treatment. Objective: To investigate whether measuring thiopurine metabolites in circulation can improve the effectiveness and safety of azathioprine treatment in patients with atopic dermatitis and/or chronic hand/foot eczema. Methods: Azathioprine metabolite levels were measured in eczema patients during maintenance treatment (Part I) and dose escalation (Part II). Clinical effectiveness, hepatotoxicity, and bone marrow suppression were analyzed and TPMT genotype was assessed. Results: A wide variation in metabolite levels in all dose groups was observed. In Part I (32 patients), there were no significant differences in 6-TGN levels between clinical responders and non-responders (p = .806). No hepatoxicity or myelotoxicity was observed. In Part II, all 6-TGN and 6-MMP levels increased during dose escalation. Hypermethylation was observed in 2/8 patients. Conclusion: For individual eczema patients treated with azathioprine, routinely measuring 6-TGN and 6-MMP can be helpful in optimizing azathioprine dose, improving clinical effectiveness, and preventing side effects.

Increased liver enzyme levels during azathioprine treatment; beware of concomitant use of proton pump inhibitors

Azathioprine (AZA) is a purine antagonist, which is frequently used off label in chronic inflammatory skin diseases. Genetic polymorphisms in thiopurine S-methyltransferase (TPMT) influence the metabolism of AZA. A reduced enzymatic activity of TMPT is associated with increased 6-thioguaninie nucleotide (6-TGN) levels which may cause severe leukopenia. High TPMT activity is associated with increased 6-methylmercaptopurine (6-MMP) levels (toxic 6-MMP >5700 pmol/8x10(8) RBCs), which is associated with liver toxicity.(1) Alanine transaminase (ALT) >3 upper limits of normal has been identified as a sensitive, but not necessarily specific signal of liver toxicity.(2) In daily practice AZA is often started with a test dose of 50 mg/day for 1-2 weeks. If laboratory tests show no abnormalities, the dose is increased to up to 150-200 mg/day. This article is protected by copyright. All rights reserved.

479 Model-Based Lidocaine Dosing Regimen for Seizure Control in Preterm and Term Neonates

Objectives: Lidocaine is administered as an anticonvulsant to neonates that are not responding to first-line anticonvulsants. For term neonates a dosing regimen has been developed (Malingre et al., 2006), but it has not been evaluated for preterm neonates. The objective of this study was to develop an optimal dosing strategy for lidocaine in preterm and term neonates on basis of a newly developed population PK model. Methods: Simulations were performed using NONMEM 6.2. Several requirements were defined: Results: A body weight-based infusion strategy was developed using simulations. First, a bolus injection was chosen for all weight categories for rapid achievement rapid seizure control. This was followed by a 4-hour loading infusion. Then dosing was reduced in two steps during 6 and 12 hours, respectively. (regimen not shown) With this regimen, the median concentration achieved at the end of the 4-hour infusion was 6.3 mg/L, (IQR 1.8 mg/L). Only 3.6% of the simulated individuals had concentrations >9.0 mg/L. This new strategy should be a safe and effective regimen for neonatal seizure control. Prospective validation is in progress.