Stability of drug concentrations in plasma stored in serum separator blood collection tubes

The stability of therapeutic concentrations of 11 drugs (amikacin, carbamazepine, digoxin, gentamicin, lithium, methotrexate, phenobarbital, phenytoin, quinidine, theophylline, tobramycin) and two trace elements (copper and zinc) in plasma stored in serum separator ("Corvac" brand) blood collection tubes was investigated over a 1 week period of storage in the refrigerator. No significant change in concentration was noted for any analyte during the study period. Concentrations were also not significantly different from those observed during concurrent storage of the same plasma samples in nonserum separator ("Vacutainer" brand) blood collection tubes.     

Sampling time and indications appropriateness for therapeutically monitored drugs at a teaching university hospital in Oman

Objective: To evaluate prospectively the appropriateness of indications, sampling time and outcome of TDM requests at a teaching university hospital in Oman. Methods: A prospective cross-sectional study was conducted over a four months period; October 2013–January 2014 at the Sultan Qaboos University Hospital (SQUH), an 855 bed university teaching hospital. Appropriateness criteria for indications and sampling time were defined a priori. The evaluated drug’s requests were for carbamazepine, phenytoin, phenobarbital, valproic acid, digoxin, gentamicin, amikacin, vancomycin, tobramycin, theophylline, lithium, and cyclosporine. Results: Of 733 evaluated TDM requisitions, the majority were for antibiotics (75.0%) followed by antiepileptics (10.5%) and cyclosporine (8.9%). Most of the requests had appropriate indication (78.2%), however, only 28.5% had appropriate sampling time. Results were applied by dosage adjustments in 65.8% of requests and some of the inappropriately sampled requests (15.3%) were used as a basis for modifying the dosage regimen. Of all the reported plasma concentrations 42.3%, 41.2%, and 16.5% were within, below and above the reference range, respectively. Conclusion: TDM service is much less than optimal in SQUH. A lot of effort needs to be carried out to improve TDM use in the developing countries as adjusting the doses on results that are based on wrong sampling time might expose patients to toxicity or therapeutic failure.     

2010～2012年度治疗药物监测室间质评结果分析

目的分析2010～2012年度治疗药物监测（TDM）项目室间质评结果,为提高TDM检测质量提供依据。方法收集2010～2012年参加卫生部临床检验中心全血TDM室间质评的3次结果和血清TDM室间质评医院的6次调查结果,对结果进行统计分析。结果全国开展全血TDM室间质评的医院数从2010年88家增加至2012年102家,开展血清TDM室间质评的医院数从2010年119家增加至2012年136家。全血TDM中,环孢霉素A、他克莫司、西罗莫司的3年平均合格率分别为94．2％、83．4％、89．1％。血清TDM中,茶碱、地高辛、苯妥英、丙戊酸、卡马西平的3年平均合格率分别为94．3％、81．9％、95．4％、96．7％、95．9％。参加实验室的所有方法中,偏振荧光免疫法的应用逐年减少,吖啶酯直接化学发光法和酶增强免疫分析法的应用逐年增加。在3年195个批号的室间质评中,约92．3％批次的方法间变异系数小于20％;7．2％批次方法间变异系数在20％～30％之间;0．5％批次的方法间变异系数大于30％。结论我国TDM室间质评检测质量尚有待提高,应加强TDM的质量控制,推动TDM检测结果的准确、可比,为临床提供可靠的诊疗依据。     

Therapeutic drug monitoring in Turkey: experiences from Istanbul

Therapeutic drug monitoring (TDM) has assumed an important place in patient management in the last few decades. In this study, serum drug levels determined in 7759 specimens sent to the Department of Pharmacology and Clinical Pharmacology in 1994 and 1998 for TDM were retrospectively evaluated. Monitored drugs were carbamazepine, valproate, phenytoin, phenobarbital, digoxin, theophylline, and salicylate. The comparison of the results obtained for the relevant 2 years showed that there was a remarkable increase in the number of requests for TDM per year and in the rate of serum drug levels that were within therapeutic range. Serum antiepileptic drug level monitoring accounted for a major part of the data. Overall data suggest that the use of TDM in antiepileptic drugs is improving; conversely, digoxin and theophylline are still not being properly monitored. In this study, the results are discussed in the light of rational TDM criteria.     

The binding of selected therapeutic drugs to human serum alpha-1 acid glycoprotein and to human serum albumin in vitro

The binding of acetaminophen, lidocaine, phenobarbital, phenytoin, theophylline, and valproic acid to human serum alpha-1 acid glycoprotein (orosomucoid) and to human serum albumin separately in vitro was investigated using equilibrium dialysis of the unlabeled drugs. Each drug was studied at a therapeutic concentration. Alpha-1 acid glycoprotein was studied at one elevated and two physiological concentrations, whereas albumin was studied at one physiological and two low concentrations. The nonphysiological concentrations were consistent with those that might be seen in a variety of clinical conditions. Acetaminophen, phenobarbital, theophylline, and valproic acid showed negligible binding to alpha-1 acid glycoprotein. However, lidocaine and phenytoin demonstrated binding to this protein, and increases in the alpha-1 acid glycoprotein concentration produced decreases in the unbound (free) or "active" concentration of these two drugs. All drugs but acetaminophen bound to albumin, and decreases in the albumin concentration yielded increases in the unbound (free) or "active" concentration of the remaining 5 drugs. These findings are significant when lidocaine, phenytoin, phenobarbital, theophylline, or valproic acid are used in patients with clinical conditions that may affect the concentration of these two binding proteins.     

三年来我室TDM室间质评结果回顾

目的：对我室３年来ＴＤＭ室间质评估结果的准确性作一个客观的评价,同时分析存在的问题及产生这些问题的原因。方法：对我室３年来参加室间质评的茶碱,苯妥英,地高辛３个监测品种的平均成绩进行纵向及横向对比,分析。结果;茶碱和苯妥英成绩较好,地高辛成绩呈逐年上升的趋势。结论;通过采取一系列有效措施后,我的治疗药物监测可成为临床用药较为可靠的参考。     

Herbal supplements and therapeutic drug monitoring: focus on digoxin immunoassays and interactions with St. John's wort

Herbal supplements can affect concentrations of therapeutic drugs measured in biological fluids by different mechanisms. Herbal products can either directly interfere with the methodology used in the measurement of drugs or indirectly interfere by altering the pharmacokinetics of coadministered drugs. The active components of Chan Su, Lu-Shen-Wan, Dan Shen, Asian and Siberian ginseng, oleander containing supplements, and Ashwagandha interfere with digoxin measurements by immunoassays, especially the polyclonal antibody-based immunoassays. Herbal supplements are sometimes contaminated with Western drugs causing drug toxicity. A therapeutic drug monitoring (TDM) service is very helpful for diagnosis of drug toxicity in such patients. Herbal products such as St. John's wort, a popular herbal antidepressant, increase the clearance of certain drugs either by increasing the activity of liver or intestinal cytochrome P-450 mixed-function oxidase or through modulation of the P-glycoprotein efflux pump. Significantly reduced concentrations of various therapeutic drugs such as digoxin, theophylline, cyclosporine, tacrolimus, tricyclic antidepressants, warfarin, and protease inhibitors can be observed due to interaction of these drugs with St. John's wort, causing treatment failure. On the other hand, a few drugs such as carbamazepine, mycophenolic acid, and procainamide do not show any interaction with St. John's wort. Understanding the effect of herbal products on TDM methodologies and identification of interactions between herbal products and drugs by TDM are very important clinically.     

The effect of parenteral nutrition fluids on the binding of therapeutic drugs to human serum in vitro

The competitive binding of seven therapeutic drugs (carbamazepine, phenytoin, phenobarbital, procainamide, quinidine, theophylline, and valproic acid) to human serum and to five commonly used parenteral nutrition fluids in vitro was studied using equilibrium dialysis. For five of the drugs, all parenteral nutrition fluids bound less drug than human serum-phenobarbital (up to 14% less), phenytoin (up to 46% less), procainamide (up to 43% less), quinidine (up to 25% less), and valproic acid (up to 77% less)-suggesting that the presence of these fluids might increase the free fraction of these drugs in vivo. For carbamazepine, the fluids bound up to 82% more drug, suggesting that the presence of these fluids might decrease the free fraction of this drug in vivo. For theophylline, the fluids produced a minimal (no more than 5%) effect on binding to serum. The administration of parenteral nutrition fluids may significantly alter the free (active) fraction of some therapeutic drugs.     

Development and clinical applications of the dried blood spot method for therapeutic drug monitoring of anti‐epileptic drugs

Anti‐epileptic drugs (AEDs) have various pharmacokinetic profiles, inter‐individual variabilities, high possibilities of drug‐drug interactions and narrow therapeutic indices. To provide optimal treatment for patients, therapeutic drug monitoring (TDM) is necessary. However, TDM requires sufficient quantities of blood samples to measure drug concentrations. Therefore, TDM could be a burden, particularly in paediatric cases. A good alternative that overcomes these disadvantages is the dried blood spot (DBS) method, which is simple, convenient to use and less invasive, requiring a lower quantity of blood than traditional blood sampling methods. However, the DBS method is affected by haematocrit (Hct) levels to varying extents depending on the drug properties. In addition, different papers with varying characteristics are available for use when applying the DBS method. Therefore, it has not yet been applied to TDM in clinical practice. To achieve this, several steps are required, including method development, method validation and clinical validation. Currently, the development status of the DBS method is different for each AED and unclear. Therefore, we assessed the development status of the following 19 AEDs in 26 studies: lamotrigine, valproic acid, levetiracetam, phenytoin, topiramate, carbamazepine, carbamazepine epoxide, gabapentin, phenobarbital, pregabalin, clobazam, clonazepam, ethosuximide, felbamate, monohydroxycarbamazepine, nitrazepam, rufinamide, vigabatrin and zonisamide. Among them, carbamazepine, lamotrigine, topiramate and valproic acid have been developed such that they are nearly available for TDM. In addition, Whatman 903 Protein Saver Cards and concentration analysis by liquid chromatography with triple quadrupole mass spectrometer were used most often.     

Effects of phenobarbital,clonazepam, valproic acid,ethosuximide, and phenytoin on the delayed matching-to-sample performance of pigeons

The effects of phenobarbital, clonazepam, valproic acid, ethosuximide, and phenytoin were examined in pigeons performing under a delayed matching-to-sample procedure. Clonazepam, valproic acid, ethosuximide, and phenytoin typically reduced the rate of responding to the sample stimulus, whereas phenobarbital usually increased response rates at high doses. Phenobarbital, clonazepam, and valproic acid produced generally dose-dependent decreases in accuracy; ethosuximide and phenytoin failed to do so. These results suggest that there are qualitative as well as quantitative differences in the effects of anticonvulsant drugs under the delayed matching-to-sample procedure.     

Effect of coadministered drugs and ethanol on the binding of therapeutic drugs to human serum in vitro

The effects of coadministered drugs and ethanol on the binding of therapeutic drugs to human serum in vitro was investigated. Acetaminophen, lidocaine, phenobarbital, quinidine, theophylline, and valproic acid were added to pooled human serum at therapeutic concentrations. To each preparation was added one additional drug at three concentrations ranging from therapeutic to toxic. The following eight target drug/added drug combinations were studied: acetaminophen/phenobarbital. acetaminophen/theophylline, lidocaine/quinidine, phenobarbital/acetaminophen, phenobarbital/valproic acid, quinidine/lidocaine, theophylline/acetaminophen, and valproic acid/phenobarbital. Each serum without the other added drug as well as the serum supplemented with the other drug at the three concentrations was dialyzed against phosphate buffer. Similarly dialyzed were phenobarbital, quinidine, and theophylline, both alone at therapeutic concentrations in serum and with ethanol at three different concentrations in serum. The percentage of drug binding in each preparation was calculated. Acetaminophen diminished the binding of theophylline to human serum by a net change of 5.7% (percentage increase in free drug fraction [FDF], 11.0%) at 662 micromol/L and by a net change of 7.1% (percentage increase in FDF, 13.7%) at 1324 micromol/L. Theophylline decreased the binding of acetaminophen by a net change of 6.8% (percentage increase in FDF, 8.8%) at 277.5 micromol/L; phenobarbital reduced it by a net change of 6.6% (percentage increase in FDF, 8.5%) at 431 micromol/L. Valproic acid diminished binding of phenobarbital by a net change of 9.9% (percentage increase in FDF, 21.2%) at 1732 micromol/L. No significant effects were noted with other drug combinations or with the addition of ethanol. Coingestion of acetaminophen with theophylline, phenobarbital with acetaminophen, and valproic acid with phenobarbital at high to toxic concentrations decreases the binding of the target drug. The resulting increase in free drug concentration may lead to enhanced drug effect in vivo.     

Time-dependent absorption of therapeutic drugs by the gel of the Greiner Vacuette blood collection tube

Stability of therapeutic drugs in sera collected in Becton-Dickinson VACUTAINER serum separator SST tubes has been well studied. Recently, the Greiner Vacuette serum separator tube has become available for blood collection. However, stability of therapeutic drugs in sera when the specimen is collected in the Greiner tube has not been reported. The authors studied the stability of 15 commonly monitored drugs in sera when stored on the gel of the Greiner serum separator tubes. The drugs studied were amikacin, gentamycin, tobramycin, vancomycin, digoxin, quinidine, theophylline, carbamazepine, phenobarbital, phenytoin, valproic acid, tricyclic antidepressants, salicylate, acetaminophen, and ethanol. The authors compared the concentrations of drugs in sera stored in plain tubes (no gel) and in sera stored in the Greiner tubes containing serum separator gel. They observed a significant decline in the concentrations of tricyclic antidepressants when stored in the Greiner tubes. Interestingly, concentrations of amitriptyline declined more than its metabolite nortriptyline and concentration of imipramine also decreased more than its metabolite desipramine. The concentration of carbamazepine also decreased slightly over time when serum was stored in the Greiner tube. Although declines in carbamazepine concentrations on prolonged storage in the Greiner tubes were statistically significant, the decreases may not be clinically significant. The concentrations of the other drugs studied did not decline when stored in the Greiner tubes. The authors conclude that the Greiner brand tube is not suitable for blood collection for analysis of tricyclic antidepressants.     

A correlation between the levels of phenobarbital, phenytoin and valproic acid in the blood serum and in saliva from children treated due to epilepsy

Blood serum and saliva levels of phenobarbital, phenytoin and valproic acid were estimated in children treated due to epilepsy. The ratio between the levels of the above drugs in saliva and blood serum can be of importance in calculating approximated levels of the drugs without a need of inconvenient inserting of needle and taking blood in children.     

儿童抗癫痫药物治疗药物监测

抗癫痫药物（AEDs）是治疗癫痫的主要药物,现有27种抗癫痫药物,这使得治疗药物监测（TDM）的应用越来越广泛,同时,抗癫痫药物也是进行TDM最常见的药物。第一代抗癫痫药物卡马西平、苯巴比妥、苯妥英钠、乙琥胺、扑米酮、丙戊酸在TDM方面积累了很多经验,现在TDM将更多地应用于新的抗癫痫药物如醋酸艾司利卡西平、非氨酯、加巴喷丁、拉科酰胺、拉莫三嗪、左乙拉西坦、奥卡西平、吡仑帕奈、哌拉西坦、普瑞巴林、瑞替加滨、卢非酰胺、司替戊醇、噻加宾、托吡酯、氨己烯酸和唑尼沙胺。本文通过对样本类型、样本的采集和处理、参考范围的概念进行综述,旨在为儿童抗癫痫用药的药物监测提供依据。     

Therapeutic monitoring of antiepileptic drugs: a comparison between a Czech and a Swedish University Hospital

Plasma concentrations obtained during routine therapeutic monitoring of antiepileptic drugs (AED) (N03A ATC group) were compared in patients treated with one or several AED in the University Hospitals in Ostrava, Czech Republic and Huddinge, Sweden. Request and reply forms for therapeutic drug monitoring (TDM) were used as a source of mean plasma concentrations (PC). The study included 2,824 adult out- and inpatients in Huddinge treated from 1995 to 1999 and 1,268 outpatients treated in Ostrava from 1993 to 2004. PC of valproic acid in Huddinge and all AED except clonazepam in Ostrava were analyzed with gas-liquid chromatography. Plasma concentrations of clonazepam in Ostrava and all AED except valproic acid in Huddinge were analyzed by HPLC. The differences in PC were tested by Student's t-test. Chi(2) method was used for the differences in the distribution of PC relative to the therapeutic window. The mean plasma concentrations generally reached the apparent therapeutic ranges but were below the range in the cases of phenytoin monotherapy in both hospitals, and clonazepam, phenobarbital and phenytoin in polytherapy in Ostrava. In monotherapy 33% of the analyses showed sub-therapeutic concentrations in Huddinge, compared to 38% in Ostrava. Eight percent of the analyses showed potentially toxic concentrations in Huddinge, but only 3% in Ostrava. The highest number of sub-therapeutic concentrations was detected for phenytoin in both hospitals: 59% in Huddinge, 78% in Ostrava. In polytherapy only slight differences between the hospitals were found. PC/dose ratios were significantly lower in polytherapy than in monotherapy for carbamazepine and valproic acid in both hospitals. In contrast a higher PC/dose ratio was found in polytherapy for phenytoin in both cohorts and for lamotrigine in Ostrava. Drug treatment of epilepsy in our two hospitals is surprisingly similar in terms of achieved plasma concentrations, in spite of socioeconomic and cultural differences between our two countries. This may be explained by the long experience with TDM in both hospitals, which has the inherent capacity to promote evidence based drug therapy.     

我院常规血药浓度监测结果评析

目的：对2007年1～12月间我院常规监测的6种药物血药浓度进行分析,探讨治疗药物监测在临床上的应用价值。方法：应用荧光偏振免疫分析法测定苯妥英、地高辛、环孢素等6种药物的血药浓度,并对测定结果的概况进行评析。结果：共监测1291例患者的血药浓度,其中苯妥英是6种药物中不在有效浓度范围内例数最多的一种药物,也是出现临床中毒反应最多的一种药物。地高辛和环孢素是临床药物治疗中需要密切监测药物疗效和调整药物剂量的药物。结论：苯妥英、地高辛、环孢素是最需要经常监测的药物品种。     

Unbound plasma phenytoin concentrations measured using enzyme immunoassay technique on the cobas MIRA analyser--in vivo effect of valproic acid.

This communication describes a modification of the total plasma phenytoin enzyme immunoassay technique (EMIT) run on the Cobas MIRA analyser that allows quantitation of unbound phenytoin concentrations in human plasma for routine therapeutic drug monitoring (TDM) purposes. An application of this method is also presented to consider the previously described protein binding drug interaction with concomitantly administered valproic acid in patients with epilepsy. The coefficients of variation for the unbound phenytoin assay ranged from 7.5 to 9.6% and the assay had a reproducibility and accuracy similar to the total phenytoin assay, acceptable for routine TDM. Phenytoin protein binding was linear over a range of total plasma concentrations of 3-65 mg/L. Patients also receiving valproic acid (nine patients, 105 specimens) had a significantly (p less than 0.0001) greater mean +/- SD unbound phenytoin fraction (13.3 +/- 3.1%) compared to nine patients (110 specimens) not receiving valproic acid (8.3 +/- 1.6%). There was also a significant correlation (p less than 0.001) between plasma valproic acid concentration and unbound phenytoin fraction, which resulted in greater intrasubject variability in phenytoin protein binding.     

某三甲综合医院治疗药物监测中危急值的回顾性分析

目的：探讨2019-2020年间,河南省人民医院常规开展的13种治疗药物监测项目的危急值数据所呈现的特点及对个体化用药的启示。方法：通过查询该院危急值报告记录与处置登记本和瑞美实验室管理系统（LIS）,对近2年在TDM中出现的危急值的项目、科室来源、患者基本情况等进行统计,使用SPSS 21.0和EXCEL 2019进行数据分析。结果：共出现危急值4 152例（发生率8.7%）,危急值发生率前三位的项目为：苯妥英（64.5%）、地高辛（28.6%）和万古霉素（24.8%）;危急值构成比前三位的项目为：伏立康唑（24.0%）、他克莫司（19.3%）和丙戊酸（13.6%）;科室来源前三位为：感染科、移植科和神经内科;从患者的基本资料来看,危急值发生率较高的为中青年男性患者。在TDM中出现危急值的原因众多,其中患者依从性较差和样本采集时间错误是出现假阳性结果的主要原因之一。结论：定期对TDM中出现的危急值数据进行回顾性的统计分析,不仅有利于提高患者的个体化治疗效果,保障用药安全,还有利于检测科室的查缺补漏,为危急值的持续性改进提供了证据支持。     

Recent advances in analytical methods for the therapeutic drug monitoring of immunosuppressive drugs

Therapeutic drug monitoring (TDM) of immunosuppressive drugs (ISDs) with a narrow therapeutic index is an increasingly popular tool for minimizing drug toxicity while maximizing the prevention of graft loss and organ rejection. This review focuses on trends regarding analytical methods for the TDM of ISDs since 2011. The five most commonly prescribed immunosuppressive medications are critically reviewed: cyclosporine A, tacrolimus, sirolimus (rapamycin), everolimus, and mycophenolic acid. This review introduces the general background of TDM and ISDs and presents the recent developments in using liquid chromatography–tandem mass spectrometry (LC–MS/MS) and immunoassays for the TDM of ISDs. Finally, a future perspective for these analytical methods is briefly discussed.