Therapeutic Drug Monitoring Purposes Research Articles

ChemInform Abstract: Optimization of Antimicrobial Therapy Based on Therapeutic Drug Monitoring

AbstractReview: 17 refs.

Determination of puerarin in pharmaceutical and biological samples by capillary zone electrophoresis with UV detection

A rapid and efficient capillary zone electrophoresis (CZE) method with ultraviolet detection has been successfully developed for the determination of puerarin in Xinkeshu capsules and biological samples. The optimal CZE conditions were determined to be 70mM H3BO3–Na2B4O7, pH 9.2, injection time 5s, applied voltage 25kV, working temperature 25°C and detection wavelength 254nm. Under these conditions, a linear range from 17.3 to 138μg/mL with the correlation coefficient of 0.9998 and limit of detection of 34.6ng/mL (S/N=3) for puerarin were obtained. The relative standard deviation of the migration time and peak area of puerarin were 0.23–0.91, 0.43–1.62, 0.10–0.64 and 0.64–1.32% for intra-day and inter-day analyses, respectively. Satisfactory results were obtained for recovery and repeatability. The proposed method was successfully applied to analyze the puerarin content in Xinkeshu capsules and some biological samples with good results. It is suitable for applications in pharmaceutical industries for quality control and in clinical laboratories for therapeutic drug monitoring purposes.

Determination of ribavirin in human serum using liquid chromatography tandem mass spectrometry

A method has been developed for the determination of ribavirin in human serum for therapeutic drug monitoring purposes, using liquid chromatography electrospray ionization mass spectrometry. Separation was obtained with a mobile phase gradient starting and ending in 100% aqueous conditions using a Waters Atlantis® T3 column (100×2mm, 3μm). The entire sample preparation consisted of dilution, followed by ultrafiltration. From the clear ultrafiltrate 5μL was injected on the LC–MS/MS system. The calibration curves were linear in the range of 0.2–10mg/L with within-run and between-run precisions (CVs) in the range of 0–10%. The method was validated with respect to specificity, selectivity, linearity, accuracy, precision, recovery and stability and meets the requirements of the FDA. The method was extensively tested for matrix effects by determining the variation of the slopes of calibration curves in different sources of serum and plasma. This method is suitable for the determination of ribavirin in human serum for therapeutic drug monitoring.

Optimization of Antimicrobial Therapy Based on Therapeutic Drug Monitoring

Recently, the pharmacokinetic (PK)-pharmacodynamic (PD) theory draws attention in the therapy of the infectious disease. Although the theory was only introduced into the field of antimicrobial therapy several years ago, the foundation was in the individualization of administering design by therapeutic drug monitoring (TDM) begun 30 years ago. Although, the main purpose of TDM that had been performed so far was assumption of the evasion of the side effects caused with antimicrobials, it is difficult to say that it has been used as a tool to improve the efficacies. Furthermore, although the information described in the package inserts of antimicrobials must be important grounds to use the agents properly, it was recently recognized that there were pitfalls in PK-PD region. In this review, the following three items are described; 1) problem of dosage regimen described in package insert of antimicrobials, such as aminoglycosides and vancomycin in our country, and findings accumulated through their TDM; 2) strategy for proper use of antimicrobials based on PK-PD theory; 3) finally, the role of the pharmacist expected in the area of the infectious disease treatment.

The use of dried blood spots as sample collection for the therapeutic drug monitoring of atypical antipsychotics

Introduction: The collection of blood samples on filter papers, known as dried blood spots (DBS), is an established technique for the screening of newborn errors of metabolism. Recently, there is a large evidence for its use in the therapeutic drug monitoring (TDM) field for the quantitative analysis of small molecules. The collection of whole blood as DBSs has many advantages in comparison to conventional plasma sampling: smaller sample volumes, less invasive withdrawal, easier storage and shipment, less requirements for biohazard arrangements. In the last decade numerous analytical methods have been developed in our Laboratory of Pharmaco-Toxicological Analysis for the plasmatic monitoring of several Central Nervous System drugs in collaboration with national and foreign Psychiatric Clinics. Thus, the DBS technique as sample collection could be advisable for TDM purposes of atypical antipsychotics. Methods: Some analytical methods by means of high performance liquid chromatography coupled with both electrochemical and spectrophotometric detectors have been implemented for the analysis of clozapine, olanzapine, risperidone and aripiprazole in DBSs from psychiatric patients. Blood was spotted onto filter papers and allowed to dry. The quantitative assays employed simple solvent extraction of the analytes from the DBS samples, followed by solid-phase extraction (SPE) or micro-SPE procedures for the clean-up of the biological samples. Results: Preliminary results showed good extraction yield values of clozapine and risperidone from DBSs, being always higher than 85.0%. Results were satisfactory in terms of sensitivity and selectivity. Moreover, preliminary stability data showed that the samples in the DBS form can be stored for a long period of time before the analysis without the need of refrigeration or any particular arrangements. Clozapine and risperidone levels obtained from DBSs were in good agreement with those obtained from plasma analysis [1,2] after multiplying the DBS values by 1.8. Discussion: Assays are currently in progress to validate the methods in terms of linearity, precision and accuracy and to apply them to TDM of numerous patients treated with clozapine, olanzapine, risperidone and aripiprazole.

Clozapine—A dangerous drug in a clozapine-naïve subject

Clozapine is a uniquely effective antipsychotic, but is very toxic in clozapine-naïve subjects. A 34-year-old male patient in a mental health facility, who was not prescribed clozapine, took 350 mg clozapine obtained from another patient at night. He was found dead the next morning. The presence of cardiomegaly related to obesity may have increased the risk of suffering an acute cardiac event after ingestion of clozapine. The medication prescribed to the patient was not thought to have contributed to the fatal outcome. Post mortem femoral blood clozapine and norclozapine concentrations were 0.48 and 0.20mg/L, respectively. By way of comparison, audit of 104,127 plasma samples (26,796 patients) assayed for therapeutic drug monitoring purposes 1993-2007, showed plasma clozapine 0.35 mg/L or more in 57.5% samples (8.4% 1mg/L or more). Those involved in the investigation of clozapine-associated deaths need to be aware that that death in an adult may occur after a single 'therapeutic' dose. A diagnosis of fatal clozapine poisoning cannot be made solely on the basis of a post mortem blood clozapine measurement.

Measurement of serum lamotrigine by high performance liquid chromatography using a phenyltriazine as internal standard

Lamotrigine, an anti-epileptic drug with a phenyltriazine molecular structure, is commonly measured for therapeutic drug monitoring purposes by high performance liquid chromatography (HPLC) or gas liquid chromatography (GLC). A convenient internal standard is the structurally related phenyltriazine compound BWA725C previously obtainable from the Wellcome Foundation, UK. Irsogladine is also structurally similar to lamotrigine and was therefore tested as a possible replacement for BWA725C. A GLC procedure with thermionic detection (NPD) has been utilized routinely for lamotrigine in our drug monitoring facility. Irsogladine was unsuitable, however, because the retention times of irsogladine and a co-prescribed drug, carbamazepine, were very similar. An HPLC method utilizing a Prodigy Phenomenex ODS3 column performed well using either of the internal standards. The pH of the mobile phase had a distinct impact on the spectra of lamotrigine and BWA725C. A mobile phase at pH 3, with detection at 225 nm was required to effectively resolve lamotrigine from sulthiame and irsogladine from phenobarbitone. Comparison of the HPLC and the existing GLC method with routine patient specimens (n = 43) gave an equation, y = 0.9382x + 0.8238, R(2) = 0.9862. Irsogladine was found to be a suitable internal standard for an HPLC analysis of lamotrigine.

Rapid assays of clozapine and its metabolites in dried blood spots by liquid chromatography and microextraction by packed sorbent procedure

A novel analytical approach has been developed for the determination of clozapine and its metabolites in dried blood spots on filter paper, using a chromatographic method coupled with a microextraction by packed sorbent procedure. The analytes were separated on a RP-C18 column using a mobile phase composed of 20% methanol, 16% acetonitrile and 64% aqueous phosphate buffer. Coulometric detection was used, setting the guard cell at +0.050 V, the first analytical cell at −0.200 V and the second analytical cell at +0.500 V. Clozapine and its metabolites were extracted from dried blood spots with phosphate buffer and, then, a microextraction by packed sorbent procedure for the sample clean-up was implemented obtaining good extraction yields. The calibration curve was linear over the 2.5–1000 ng mL −1 blood concentration ranges for all the analytes. The method validation gave satisfactory results in terms of sensitivity, precision, selectivity and accuracy. The analytical method was successfully applied to dried blood spots from several psychiatric patients for therapeutic drug monitoring purpose.

Determination of l-dopa, carbidopa, 3- O-methyldopa and entacapone in human plasma by HPLC–ED

The aim of the study was the development of analytical methods suitable for the quantification of l-dopa, carbidopa and entacapone in plasma of Parkinsonian patients treated with Stalevo ®. The metabolite 3- O-methyldopa was also determined to obtain some indications on the pharmacokinetics of l-dopa. For the simultaneous analysis of l-dopa, 3- O-methyldopa and carbidopa, a RP C18 column as the stationary phase and a mixture of methanol and a pH 2.88 phosphate buffer (8:92, v/v) as the mobile phase were used. A feasible plasma pre-treatment based on protein precipitation was implemented, obtaining extraction yield higher than 94% for all the analytes. For the analysis of entacapone a RP C8 column and a mixture of methanol, acetonitrile and a pH 1.90 phosphate buffer as the mobile phase (17.5:22.5:60, v/v/v) were used. A plasma pre-treatment procedure was developed, based on solid phase extraction of entacapone using Oasis HLB cartridges. Extraction yields were good, being always higher than 96%. Both methods, based on HPLC–ED ( V = +0.8 V), have been fully validated. Good linearity was obtained over the following concentration ranges: 100–4000 ng mL −1 for l-dopa, 200–10,000 ng mL −1 for 3- O-methyldopa, 25–4000 ng mL −1 for carbidopa and 20–4000 ng mL −1 for entacapone. Precision data were satisfactory, being R.S.D.% values lower than 5.64%; accuracy also resulted very good with recovery data higher than 90%. The proposed methods have been successfully applied to the analysis of patient plasma samples and seem to be suitable for therapeutic drug monitoring purposes.

A Simple Dried Blood Spot Assay for Therapeutic Drug Monitoring of Lamotrigine

Blood spot collection cards can be easily used to obtain specimens for analysis of drugs for the purpose of therapeutic drug monitoring. In this work, the development and validation of a simple technique for the determination of lamotrigine from dried blood spots is described. The method is based on liquid chromatography with ultraviolet detection. The intra- and inter-day precision (measured by CV%) was less than 11%. The accuracy (measured by relative error %) was less than 12%. The limits of detection and quantification were calculated to be 0.12 and 0.2 μg mL−1 respectively. The small volume of blood required (10 μL), the short analysis time (less than 4 min), combined with the simplicity of the analytical technique makes this a useful procedure for monitoring lamotrigine concentrations. Our preliminary experience with the developed method indicated that it can be implemented in routine clinical setting.

Determination of Ciprofloxacin in Dried Blood Spots for Therapeutic Drug Monitoring

The use of blood spot collection cards is a simple way to obtain specimens for analysis of drugs for the purpose of therapeutic drug monitoring, assessing adherence to medications and preventing toxicity in certain groups of patients. We describe the development and validation of a microanalytical technique for the determination of ciprofloxacin from dried blood spots. The method is based on reversed phase liquid chromatography with fluorescence detection. Drug recovery in the developed method was found to be higher than 95%. The limits of detection and quantification were calculated to be to be 60 and 100 ng mL−1, respectively. The intra- and inter-day precision (measured by CV%) was always less than 6% (13.07% at LOQ). The accuracy (measured by relative error, %) was always less than 8% (7.82% at LOQ). Stability analysis showed that ciprofloxacin is stable for at least 1 month when stored at −70 °C. The small volume of blood required (30 μL), combined with the simplicity of the analytical technique makes this method a potential procedure for monitoring ciprofloxacin concentrations in certain patient populations.

Determination of orphenadrine plasma levels using HPLC with diode array detection and a novel solid-phase extraction procedure in psychiatric patients

Orphenadrine is an antimuscarinic agent mainly used for the treatment of parkinsonism and to alleviate the neuroleptic syndrome induced by antipsychotic drugs. A new, rapid analytical method, based on liquid chromatography with diode array detection (DAD), has been developed and applied to the determination of orphenadrine in plasma of schizophrenic patients for therapeutic drug monitoring and toxicological purposes. The chromatographic separation was performed on a pentafluorophenyl reversed phase column with a mobile phase composed of acetonitrile–phosphate buffer mixture. DAD detection was carried out at 220 nm. A careful and rapid solid-phase extraction procedure on cyanopropyl cartridges was chosen for plasma sample purification and pre-concentration obtaining good extraction yield values for the analyte (>96.0%). The assays showed a linear response for orphenadrine (30–1000 ng mL −1). The method is also precise and selective. Thus, the method developed seems to be suitable for routine analysis of orphenadrine in psychiatric patients. Moreover, it was applied to plasma samples from a psychotic patient who had tried to poison himself with 1000 mg of orphenadrine and was undergoing polypharmacy.

Current Technologies and Considerations for Drug Bioanalysis in Oral Fluid

Drug oral fluid analysis was first used almost 30 years ago for the purpose of therapeutic drug monitoring. Since then, oral fluid bioanalysis has become more popular, mainly in the fields of pharmacokinetics, workplace drug testing, criminal justice, driving under the influence testing and therapeutic drug monitoring. In fact, oral fluid can provide a readily available and noninvasive medium, without any privacy loss by the examinee, which occurs, for instance, during the collection of urine samples. It is believed that drug concentrations in oral fluid may parallel those measured in blood. This feature makes oral fluid an alternative analytical specimen to blood, which assumes particular importance in roadside testing, the most published application of this sample. Great improvements in the development of accurate and reliable methods for sample collection, in situ detection devices (on-site drug detection kits), and highly sensitive and specific analytical methods for oral fluid testing of drugs have been observed in the last few years. However, without mass spectrometry-based analytical methods, such as liquid chromatography coupled to mass spectrometry (LC-MS) or tandem mass spectrometry (LC-MS/MS), the desired sensitivity would not be met, due to the low amounts of sample usually available for analysis. This review will discuss a series of published papers on the applicability of oral fluid in the field of analytical, clinical and forensic toxicology, with a special focus on its advantages and drawbacks over the normally used biological specimens and the main technological advances over the last decade, which have made oral fluid analysis of drugs possible.

Simultaneous CE Determination of Captopril and Indapamide in Pharmaceuticals and Human Plasma

Capillary electrophoresis with UV photo diode-array detection was utilized to adopt a new method for the assay of captopril and indapamide in pharmaceuticals and human plasma. Electrophoretic conditions controlling the analysis were optimized to develop separation, sensitivity and rapidity. The optimum conditions obtained were 100 mM borate at pH 9.0, injection time 10.0 s, voltage 25 kV and column temperature 25 °C with detection at 220 nm. Relatively, wide dynamic ranges for captopril (1–100 mg L−1) and indapamide (0.1–40 mg L−1) were obtained. Also, the method recorded acceptable intra- and inter-day accuracy (89.8–97.9%) and precision (0.77–3.50%) in pharmaceutical formulations and human plasma. The sensitivity of the method was developed by the optimization and the preconcentration conducted for human plasma sample using liquid–liquid extraction. The limit of detection gained (0.075 and 0.045 mg L−1 for captopril and indapamide, respectively) reached the level of both drugs possibly found in human plasma. The method is suitable to be applied in pharmaceutical industries for quality control and in clinical laboratories for therapeutic drug monitoring purposes.

Arzneimittelinduzierte Psychose nach Einnahme von langsam freisetzendem Methylphenidat

The case report describes the sudden emerge of psychotic symptoms of a 13-year old boy, suffering from attention deficit hyperactivity disorder (ADHD), while he was treated with a modified--release formulation of methylphenidate. The question of the attending physician, whether the symptoms indicate an early beginning of schizophrenia or whether the symptoms can be considered as an overdose phenomenon of methylphenidate should be discussed. The knowledge of the pharmacokinetics of methylphenidate as modified--release formulation and the serum concentration values of methylphenidate and its metabolite provide information for interpretation of the case reported, with regard to the purpose of therapeutic drug monitoring (TDM) for methylphenidate. Finally we conclude that the ingestion of an unintended overdose of methylphenidate may have caused the boy's psychotic symptoms and that routine therapeutic serum concentrations of methylphenidate have to be correlated to the point of time when the blood was drawn in relation to the intake of methylphenidate.

Analysis of the recent antipsychotic aripiprazole in human plasma by capillary electrophoresis and high-performance liquid chromatography with diode array detection

Two methods, based on the use of capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC), respectively, were developed for the analysis of the atypical antipsychotic aripiprazole in plasma of schizophrenic patients for therapeutic drug monitoring purposes. Good analytical performances were obtained with the CE method, using uncoated fused silica capillaries and a background electrolyte composed of 50mM phosphate buffer at pH 2.5. With 20kV voltage, aripiprazole was detectable at 214nm within 5min. The second analytical method, based on HPLC with diode array detection, employed a C8 reversed-phase column and a mixture of a 12.5mM phosphate buffer, pH 3.5, containing triethylamine and acetonitrile as the mobile phase. Aripiprazole was detected at 254nm and a complete chromatographic run lasted about 10min. For both analytical methods loxapine was used as the internal standard and the same plasma sample pre-treatment by means of solid-phase extraction on cyano cartridges was carried out, with extraction yield values always higher than 91.3%. Linear responses for aripiprazole were obtained between 70 and 700ngmL−1 and precision assays (expressed as relative standard deviation values) were lower than 7.0%. After validation, both methods were successfully applied to human plasma samples drawn from schizophrenic patients undergoing therapy with Abilify® tablets. Accuracy was satisfactory, with recovery value higher than 91.0%.

Pharmacokinetic Study of Mycophenolate Mofetil in Patients with Systemic Lupus Erythematosus and Design of Bayesian Estimator Using Limited Sampling Strategies

Monitoring of the area under the plasma concentration-time curve (AUC) of mycophenolic acid (MPA) has been developed for individual dose adjustment of mycophenolate mofetil (MMF) in renal allograft recipients. MMF is currently used as an off-label drug in the treatment of systemic lupus erythematosus (SLE), but factors of its exposition may be different in these patients and need to be determined for therapeutic drug monitoring (TDM) purposes. The aim of the study was to develop a maximum a posteriori probability (MAP) Bayesian estimator of MPA exposition in patients with SLE, with the objective of TDM based on a limited sample strategy. Twenty adult patients with SLE given a stable 1 g/day, 2 g/day or 3 g/day dose of MMF orally for at least 10 weeks were included in the study. MPA was measured by high-performance liquid chromatography (HPLC) coupled to a photodiode array detector (11 plasma measurements over 12 hours post-dose per patient). Free MPA concentrations were measured by HPLC with fluorescence detection. Two different one-compartment models with first-order elimination were tested to fit the data: one convoluted with a double gamma distribution to describe secondary concentrations peaks, and one convoluted with a triple gamma distribution to model a third, later peak. A large interindividual variability in MPA concentration-time profiles was observed. The mean maximum plasma concentration, trough plasma concentration, time to reach the maximum plasma concentration and AUC from 0 to 12 hours (AUC(12)) were 13.6 +/- 8.4 microg/mL, 1.4 +/- 1.2 microg/mL, 1.1 +/- 1.2 hours and 32.2 +/- 17.1microg . h/mL, respectively. The mean free fraction of MPA was 1.7%. The one-compartment model with first-order elimination convoluted with a triple gamma distribution best fitted the data. Accurate Bayesian estimates of the AUC(12) were obtained using three blood samples collected at 40 minutes, 2 hours and 3 hours, with a coefficient of correlation (R) = 0.95 between the observed and predicted AUC(12) and with a difference of <20% in 16 of the 20 patients. A specific pharmacokinetic model was built to accurately fit MPA blood concentration-time profiles after MMF oral dosing in SLE patients, which allowed development of an accurate Bayesian estimator of MPA exposure that should allow MMF monitoring based on the AUC(12) in these patients. The predictive value of targeting one specific or different AUC values on patients' outcome using this estimator in SLE will need to be evaluated.

Relevant Issues in the Monitoring and the Toxicology of Antidepressants

This review provides specific information concerning the interpretation and usefulness of antidepressant drug monitoring. Fifteen antidepressants (ADs) were selected based on their importance in the 7 major markets (Japan, USA, France, United Kingdom, Italy, Spain, Germany) according to the Cognos Plus Study #11. Literature data were reviewed concerning monitoring of the tricyclic ADs amitriptyline, clomipramine, imipramine, and new generation antidepressants such as citalopram, escitalopram, fluoxetine, fluvoxamine, paroxetine, sertraline, venlafaxine, mianserin, mirtazapine, bupropion, and milnacipran. In addition, St.-John's Wort was added as this natural antidepressant is very popular in Europe. The objectives of therapeutic drug monitoring (TDM) for old and new generation ADs differs, as older ADs have narrow therapeutic windows with higher risks of severe drug interactions, while the new ADs have a wide therapeutic range, but an unclear plasma concentration-effect relationship. Therefore, the purpose of TDM for new-generation ADs leads more to the monitoring of patient compliance and special patient groups such as the elderly, patients with liver and kidney impairment, patients with poor metabolism by CYP 450 and comedication with inhibitors and inducers of those enzymes.

Quetiapine and Drug Interactions

The objective of the present study was to investigate the effect of age, gender, and various comedications on the pharmacokinetics of quetiapine in a naturalistic setting. In total, 2111 serum samples analyzed for quetiapine during the period from June 2001 to December 2004 were included in the study. The samples had been collected for routine therapeutic drug monitoring purposes from 1179 patients treated with quetiapine. A log-linear mixed model was used to identify factors influencing the dose-corrected quetiapine serum concentration, expressed as the quetiapine concentration-to-dose (C/D) ratio. Variables included in the analysis were age, gender, and concomitant treatment with a total of 41 drugs most often used in combination with quetiapine. Age >or= 70 years (p = .001) and comedication with alimemazine (p = .002), fluvoxamine (p = .001), citalopram/escitalopram (p = .041), or clozapine (p < .001) significantly increased the serum concentrations of quetiapine, while age < 18 years (p = .044) and comedication with lamotrigine (p = .024), levomepromazine (p = .011), oxazepam (p < .001), or carbamazepine (p < .001) significantly decreased the serum concentrations. The effects were most pronounced for fluvoxamine (+159%), clozapine (+82%), age >or= 70 years (+67%), and carbamaze-pine (-86%). In 18% of the samples, the daily dose exceeded the currently recommended maximum of 800 mg/day. Due to the increased serum levels of quetiapine, a lower dose than usual should be considered when quetiapine is administered to elderly patients and to patients comedicated with clozapine or fluvoxamine. As the inducing effect of carbamazepine on quetiapine metabolism is very potent, cotreatment with carbamazepine cannot be recommended. On the basis of our data and pharmacokinetic considerations, the majority of drugs commonly used in psychiatry can safely be given in combination with quetiapine.

A Novel Enantioselective Microassay for the High-Performance Liquid Chromatography Determination of Oxcarbazepine and Its Active Metabolite Monohydroxycarbazepine in Human Plasma

A simple and innovative assay is described that allows the determination of the antiepileptic drug oxcarbazepine and the chiral separation of the two enantiomers of its active metabolite monohydroxycarbazepine (licarbazepine). The assay requires liquid-liquid extraction of the sample (200 microL) into tert-butyl methyl ether and dichloromethane, drying of the organic phase under a nitrogen stream, reconstitution with the mobile phase, and injection in the high-performance liquid chromatography system after filtering. Separation of oxcarbazepine, R-(-)-monohydroxycarbazepine, S-(+)-monohydroxycarbazepine, and the second-step metabolite 10,11-trans-dihydroxycarbamazepine (racemate) is achieved with a Chiralcel ODR column and potassium hexafluorophosphate/acetonitrile as mobile phase. Detection is by ultraviolet absorbance at 210 nm. Standard curves are linear (r2 > or = 0.999) over the range of 0.1 to 25 microg/mL for each analyte with a limit of quantification of 0.1 microg/mL (1 ng injected) for all compounds. Within-day and between-day precision is better than 12% and within-day and between-day accuracy is between 99% and 116% for each compound. These performance characteristics are adequate for pharmacokinetic studies and for therapeutic drug monitoring. However, because the two enantiomers of monohydroxycarbazepine exhibit similar pharmacologic activity, nonenantioselective assays are likely to be more cost-effective for therapeutic drug monitoring purposes.