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Purpose The 2020 consensus guidelines for vancomycin therapeutic monitoring recommend using Bayesian estimation targeting the ratio of the area-under-the-curve (AUC) over 24 h to minimum inhibitory concentration as an optimal approach to individualize therapy in pediatric patients. To support institutional guideline implementation in children, the objective of this study was to comprehensively assess and compare published population-based pharmacokinetic (PK) vancomycin models and available Bayesian estimation tools, specific to neonatal and pediatric patients. Methods PubMed and Embase databases were searched from January 1994 to December 2020 for studies in which a vancomycin population PK model was developed to determine clearance and volume of distribution in neonatal and pediatric populations. Available Bayesian software programs were identified and assessed from published articles, software program websites, and direct communication with the software company. In the present review, 14 neonatal and 20 pediatric models were included. Six programs (Adult and Pediatric Kinetics, BestDose, DoseMeRx, InsightRx, MwPharm++, and PrecisePK) were evaluated. Results Among neonatal models, Frymoyer et al. and Capparelli et al. used the largest PK samples to generate their models, which were externally validated. Among the pediatric models, Le et al. employed the largest sample size, with multiple external validations. Of the Bayesian programs, DoseMeRx, InsightRx, and PrecisePK utilized clinically validated neonatal and pediatric models. Conclusion To optimize vancomycin use in neonatal and pediatric patients, clinicians should focus on selecting a model that best fits their patient population and utilize Bayesian estimation tools for therapeutic AUC-targeted dosing and monitoring.

Therapeutic drug monitoring (TDM) of antiepileptic drugs provides a valid clinical tool in optimization of overall therapy. However, TDM is challenging because of the high biological sample (plasma/blood) storage/shipment costs and the limited availability of laboratories providing TDM services. Sampling in the form of dry plasma spot (DPS) or dry blood spot is a suitable alternative to overcome these issues.An improved, simple, rapid, and stability-indicating method for quantification of pregabalin (PGB) in human plasma and DPS has been developed and validated. Analyses were performed on liquid chromatography-tandem mass spectrometer under positive ionization mode of electrospray interface. PGB-d4 was used as internal standard, and the chromatographic separations were performed on Poroshell 120 EC-C18 column using an isocratic mobile phase flow rate of 1 mL/min. Stability of PGB in DPS was evaluated under simulated real-time conditions. Extraction procedures from plasma and DPS samples were compared using statistical tests. The method was validated considering the Food and Drug Administration method validation guideline.The method was linear over the concentration range of 20-16,000 ng/mL and 100-10,000 ng/mL in plasma and DPS, respectively. DPS samples were found stable for only 1 week on storage at room temperature and for at least 4 weeks at freezing temperature (-20 ± 5°C). Method was applied for quantification of PGB in over 600 samples of a clinical study. Statistical analyses revealed that 2 extraction procedures in plasma and DPS samples showed statistically insignificant difference and can be used interchangeably without any bias.Proposed method involves simple and rapid steps of sample processing that do not require a precolumn or postcolumn derivatization procedure. The method is suitable for routine pharmacokinetic analysis and therapeutic monitoring of PGB.

BACKGROUND Brivaracetam is an antiepileptic drug used as an add-on therapy for partial-onset seizures in subjects aged 4 years and older. Owing to potential drug interactions and intersubject variability in plasma concentrations, therapeutic monitoring for brivaracetam may be useful. The aim of this study was to develop a simplified method for measuring brivaracetam plasma concentrations applicable to therapeutic drug monitoring in epilepsy. METHODS An ultra high-pressure liquid chromatography-tandem mass spectrometry method was developed and validated according to current guidelines for bioanalytical methods. Sample preparation (100 µL) involved only a simple precipitation step by acetonitrile. Brivaracetam-d7 was used as internal standard. The chromatographic analysis was performed by a Synergi Fusion column using 0.1% formic acid in water/acetonitrile as a binary gradient mobile phase, at a flow rate of 0.3 mL/min. Both brivaracetam and the internal standard eluted at 1.01 minutes. This method was applied to measure trough and 1-hour postmorning dose brivaracetam plasma concentrations of 11 patients with epilepsy. RESULTS The method was validated over a concentration range of 0.10-10 mcg/mL. The mean recovery was 95%. Both intra- and inter-assay imprecision and inaccuracy were

Perampanel, a new specific non-competitive α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor antagonist, has been recently approved in the United States and the European Union for the adjunctive treatment of focal seizures and primary generalized tonic-clonic seizures associated with idiopathic generalized epilepsy. A positive relationship between plasma perampanel concentration and improvement in seizure control has been identified in regulatory trials, suggesting that therapeutic drug monitoring could be useful in optimizing clinical response in patients with epilepsy treated with perampanel. The development of a simple and broadly applicable method for measuring plasma perampanel concentrations is desirable to permit the use of TDM for this drug in clinical practice.A high-performance liquid chromatographic method with ultraviolet detection for the quantitative determination of perampanel in small aliquots of human plasma (200 μL) has been developed and validated. Sample preparation involves a simple precipitation step followed by solvent evaporation. High-performance liquid chromatographic separation is achieved on 2 reverse-phase monolithic columns in sequence connected to an ultraviolet detector (320 nm), using as mobile phase water/acetonitrile (60:40 vol/vol) mixed with 1 mL/L phosphoric acid, at a flow rate of 1.5 mL/min. Promethazine hydrochloride is used as internal standard.Calibration curves were linear over a perampanel concentration range of 25-1000 ng/mL, with correlation coefficients equal or greater than 0.998 ± 0.001 and a limit of quantitation set at 25 ng/mL. Intra- and inter-day coefficients of variation did not exceed 7.4%, and the accuracy ranged from 96.4% to 113.3%. No interference was observed from commonly coprescribed drugs.The present assay is simple, specific, and cost effective with performance characteristics suitable for TDM use.

The prophylactic use of itraconazole has dramatically reduced the incidence of fungal infections in patients after solid-organ transplantation. To further reduce this incidence, it has been suggested that plasma concentrations of itraconazole be monitored and maintained above a putative minimum target concentration of 500 ng/mL.A retrospective audit was undertaken of patients who had had a heart or lung transplant over a 14-month period (between January 1, 2010 and March 31, 2011). The itraconazole prophylaxis regimen (dose, time of last dose, time of blood collection) and plasma concentrations were recorded together with the use of concomitant antacid medication. Details of breakthrough fungal infections were documented.Eighty-four heart or lung organ transplantations were undertaken in the study period; 57 were treated prophylactically with itraconazole. Plasma concentrations of itraconazole were monitored in 56% (n = 32) of these cases. Considerable interpatient (range, 50-2000 ng/mL) and intrapatient variability in plasma concentrations was observed. The putative target was not achieved consistently in the majority of cases. All patients were taking a proton pump inhibitor. Six of the cohort developed an invasive fungal infection. None of the 3 patients for whom plasma concentrations were monitored was above the target concentration.Further clinical studies, involving monitoring of the active metabolite and attention to the importance of the stereoisomers of itraconazole, may give better insight into the appropriateness of the currently suggested minimum target concentration, whose validity remains uncertain. Formulations with improved absorption characteristics could reduce the variability of absorption with the goal of further reducing the incidence of infrequent, but life-threatening, invasive fungal infections.

The controversy still surrounds the optimal dosing regimen of tranexamic acid (TA), primary antifibrinolytic agent used in high-risk surgeries. This study compares the pharmacokinetics profile obtained from the group of patients undergoing heart surgery with the use of cardiopulmonary bypass (CPB) with the theoretical model currently used as an established dosing regimen of TA in cardiac surgery.After induction of anesthesia, TA was administered intravenously as a bolus (30 mg/kg) infused over 15 minutes. Bolus was followed by an infusion of 16 mg·kg·h TA until the end of surgery (chest closure of the sternotomy wound). Before initiation of CPB, a bolus of 2 mg/kg was given to the pump prime. Blood samples were collected at baseline and at 30-minute time intervals during the surgery and after surgery. Automated solid-phase microextraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS) were used for the determination of TA concentration. Blinded studies on monitoring of TA concentration were performed on 94 samples. Obtained results were compared with a previously described pharmacokinetic model of TA dosing.The average concentration of TA during the use of CPB was 134 mcg/mL with the relative standard deviation 27%. The observed range of TA concentrations was 70-188 mcg/mL showing that individual patients can significantly exceed the recommended levels proposed by the theoretical model. lower limit of quantification of the proposed method was 1 mcg/mL. Intra- and interday accuracy was ±10% and precision was ≤12% at all concentration levels tested.The suitability of automated solid-phase microextraction for high-throughput clinical analysis was established for the first time. The obtained pharmacokinetic profiles showed significant interpatient variation in the concentration of TA during heart surgery with the use of CPB, which confirms the need of the therapeutic monitoring of this antifibrinolytic agent.

BACKGROUND Hydroxyurea is used in the treatment of various malignancies and sickle cell disease. There are limited studies on the pharmacokinetics of hydroxyurea, particularly in pediatric patients. An accurate, precise, and sensitive method is needed to support such studies and to monitor therapeutic adherence. We describe a novel gas chromatography-mass spectrometry (GC-MS) method for the determination of hydroxyurea concentration in plasma using stable labeled hydroxyurea C N2 as an internal standard. METHODS The method involved an organic extraction followed by the preparation of trimethylsilyl (TMS) derivatives of hydroxyurea for GC-MS selected ion-monitoring analysis. The following mass-to-charge (m/z) ratio ions for silated hydroxyurea and hydroxyurea C N2 were monitored: hydroxyurea-quantitative ion 277, qualifier ions 292 and 249; hydroxyurea C N2-quantitative ion 280, qualifier ion 295. This method was evaluated for reportable range, accuracy, within-run and between-run imprecisions, and limits of quantification. RESULTS The reportable range for the method was 0.1-100 mcg/mL. All results were accurate within an allowable error of 15%. Within-run and between-run imprecisions were

The purpose of this study is to determine the feasibility of using 10-hydroxy-10,11-dihydrocarbazepine (MHD) concentration in saliva as an alternative to serum for the therapeutic monitoring of oxcarbazepine (OXC) treatment. Investigators identified subjects seen in neurology clinics at the University of Kentucky Chandler Medical Center. Patients were eligible if they agreed to participate in this study, were taking oxcarbazepine, and if a serum MHD concentration had been ordered by their physician. Unstimulated saliva specimens (0.25 mL minimum) were collected in the clinic and frozen until analysis. Blood samples were obtained by phlebotomy. Serum specimens were analyzed by a reference laboratory. Saliva MHD concentrations were determined by high-performance liquid chromatography in the Clinical Laboratory at the Cincinnati Children's Hospital Medical Center. Linear regression analysis was used to evaluate correlations. Saliva and blood specimens were collected from 28 epilepsy patients, but usable samples were obtained from only 23. The mean serum MHD concentration was 23.9 +/- 10.0 microg/mL, and the mean saliva concentration was 23.1 +/- 10.1 microg/mL. There was a significant positive correlation between the serum and saliva concentrations: saliva (y) = 0.95 serum (x) + 0.39; r = 0.941; n = 23; P < 0.001). The mean saliva:serum MHD concentration ratio was 0.96 +/- 0.15. The results of the current study indicate that the relationship between freely flowing (unstimulated) saliva and serum concentrations of MHD is sufficient for therapeutic drug monitoring. A limitation of saliva MHD monitoring is that individuals who have difficulty producing small quantities of saliva or who have viscous saliva should generally be avoided for this type of monitoring. It is also recommended to avoid saliva collection within 8 hours after OXC dosing to allow complete absorption and transformation of the parent drug.

TDM of psychotropic drugs is widely used, but there is little consensus regarding its optimal use in the clinical context. This prompted a multidisciplinary group comprised of clinical biochemists, clinical pharmacologists, and psychiatrists of the AGNP (Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie) to provide a consensus guideline. This will allow clinical psychiatrists, practitioners, and laboratory directors involved in psychopharmacotherapy to optimize TDM of antidepressants, antipsychotics, and opioid substituents. Recommendations are also given on the combined use of TDM and pharmacogenetic tests.

Typical runtimes for quantitation of immunosuppressants in whole blood based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) are in the order of a few minutes per sample. The Agilent RapidFire-MS/MS system uses solid phase extraction cartridges instead of chromatography columns and benefits from runtimes below 15 seconds. The purpose of this study was to figure out if this high-throughput instrument could be capable for application in the clinical laboratory to quantify cyclosporine A, everolimus, sirolimus, and tacrolimus.1172 measurement results from patient samples were compared between our routinely used LC-MS/MS system and the RapidFire 360 coupled to a tandem mass spectrometer. Sample preparation and routine measurement were performed using a certified kit. Imprecision and accuracy were investigated analyzing 3 commercial quality controls of different concentrations.Both measurement procedures showed excellent agreement (Pearson correlation coefficients r = 0.964-0.995). Deming regression revealed confidence intervals (95%) for slopes and intercepts of the linear equation, which covered the values 1 and 0, respectively, in almost all cases. The relative differences between both methods were marginal (1.7%-2.9%). Good intraday precision (coefficients of variation, 0.7%-9.0%) and interday precision (coefficients of variation, 2.8%-8.4%) for all immunosuppressants were achieved. The recovery of target concentrations was 81%-116%. High robustness was found with regard to linearity of the calibration lines (linear regression coefficients r ≥ 0.99). There was only negligible carry-over (cyclosporine A, 0.07%) and high endurance of the solid phase extraction cartridge (3000 injections).The RapidFire-MS/MS system provided convincing results measuring patient samples and quality control materials. Together with a high throughput and a high robustness, it could represent an alternative to LC-MS/MS instruments in therapeutic drug monitoring.

Clinical laboratory investigations used to aid antimicrobial chemotherapy of serious infection include routine sensitivity testing and, in the case of those drugs with a narrow therapeutic range, routine assays for therapeutic monitoring to assist with dosage individualization. Tests must be of a sufficiently high quality to be clinically useful. Laboratories ensure quality through standard operating procedures, internal quality control procedures, and participation in external quality assessment (EQA) programs. This article demonstrates how EQA returns to the United Kingdom National External Quality Assessment Scheme for Antibiotic Assays and the activity of the United Kingdom National Quality Assurance Advisory Panel showed marked improvement in the technical quality of assays as exemplified by gentamicin assays. The article also highlights additional quality concerns not subject to EQA.

Studies performed in the research setting suggested that saliva instead of blood may be used for therapeutic drug monitoring (TDM) of anticonvulsants in children. This is an attractive alternative because its collection is painless, and simpler and cheaper than blood drawing. Citric acid stimulation of saliva secretion facilitates sampling in the youngest patients. The aim of the study was to evaluate the suitability of saliva in routine TDM of anticonvulsants in infants and children with epilepsy. Blood and saliva samples were obtained simultaneously during routine TDM in 170 patients on chronic anticonvulsant drug therapy attending a neurology clinic. Saliva, plasma total, and plasma free concentrations of anticonvulsants were measured by high-performance liquid chromatography and enzyme multiplied immunoassay technique. Strong and highly significant correlations between saliva and plasma concentrations were found over a wide range of concentrations for carbamazepine, phenytoin, clobazam, and desmethylclobazam, and for phenobarbital in childrenor = 8 years of age (r = 0.90 to 0.97; p0.001). Correlations between saliva and plasma concentrations were poor for phenobarbital in children8 years of age and for valproate. Correlations between saliva and plasma-free anticonvulsant concentrations were equal or only slightly better than between saliva and plasma total concentrations. Citric acid-stimulated saliva constitutes a convenient alternative for TDM of carbamazepine and phenytoin therapy in pediatric patients and of phenobarbital in childrenor = 8 years of age.

There are established quality assessment schemes for the two immunosuppressive drugs that have entered routine clinical use : cyclosporine and tacrolimus. These two drugs, together with sirolimus and mycophenolic acid, have been the subject of recent consensus panel reports that have reached broad agreement on several issues relating to therapeutic monitoring of these agents. While the current quality assessment schemes are not based on validated reference methods, the data they yield on comparative assay performance are of value as a guide to patient management and for clinical studies of drug efficacy.

Itraconazole has been shown to be highly effective against a broad spectrum of fungi, particularly aspergillus. In order to achieve the desired pharmacological effect, the itraconazole plasma concentration should be > 250 ng/ml. We developed a high-performance liquid chromatography assay for the rapid determination of plasma itraconazole concentration using solid-phase extraction and small sample volume. The assay possessed linearity up to 5,000 ng/ml, sensitivity of 50 ng/ml, average recovery of 100.8%, and run-to-run precision (n = 10) for concentrations of 100, 200, and 500 ng/ml of 12, 6.6, and 5.8%, respectively. Furthermore, the assay proved to be free of interference from 48 commonly prescribed and some over-the-counter medications. We conclude that the method described here is ideally suited for the therapeutic monitoring of itraconazole.

A detailed questionnaire was distributed to the 30 Australian laboratories known to provide cyclosporin-A (CsA) therapeutic drug monitoring (TDM) services with a view to evaluating the range of approaches to such monitoring. Replies were received from all 30 laboratories. The data suggested there was a wide discordance in approaches to CsA TDM due to the fact that laboratories appeared to have adopted individual approaches to this service, both in method selection(s) and proposed therapeutic range(s). In many cases, patients served were shown to travel to more distant centers for their graft, returning to their home city/town for longer term management. Hence, services of several laboratories were involved during their clinical care. A strong mandate was received from respondents for development of national guidelines for the monitoring of CsA and other immunosuppressant drugs in order to avoid such discrepancies in the future. The approaches to external analytical quality assurance (QA) and, to a lesser extent, internal quality control (QC) were generally inadequate.

The performance of the dry-phase apoenzyme reactivation immunoassay system (ARIS) for the measurement of carbamazepine (CBZ), phenobarbital (PB), and phenytoin (PHT) concentrations in saliva was compared with fluorescence polarization immunoassay (FPIA). Blood and saliva samples were collected from 163 adult and pediatric epilepsy patients, then analyzed using both methods. Regressions between ARIS saliva CBZ, PB, and PHT concentrations, and FPIA unbound and total serum concentrations were highly correlated, but the ARIS technique was somewhat less precise than the FPIA. Valproic acid co-medication did not affect the relationships between ARIS and FPIA saliva concentrations and unbound serum concentrations of PHT, but did disrupt the relationship between ARIS and FPIA saliva PHT and total serum PHT. The sensitivity, specificity, predicted value positive (PV+) of a therapeutic concentration, and predicted value negative (PV-) of a concentration outside the therapeutic range for the ARIS saliva technique compared very well with FPIA for CBZ, PB, and PHT. The ARIS technique for CBZ, PB, and PHT saliva determination provides acceptable accuracy, precision, and sensitivity for therapeutic monitoring. In practice, the benefits of the ARIS saliva technique, including ease of collection, safety, patient/parent acceptance, and short analysis time, are striking.

In the absence of well-defined guidelines for the monitoring of plasma concentrations of clozapine, this study examined the practices of seven laboratories from four states in Australia. Laboratories analyzed 5 freeze-dried serum samples containing a mixture of clozapine and norclozapine in varying concentrations and the measurement data were analyzed for accuracy and precision. Additional information on laboratory practices was obtained through questionnaire responses. Measurement precision amongst the laboratories was good but there were significant differences in the accuracy of measurements from one laboratory. There were differences in the ranges for which assays had been validated and in suggested therapeutic ranges. These differences could have a significant impact on the interpretation of measured concentrations and patient care, and emphasize the need for consensus in this area. Repeat concentration measurements are recommended in the case of drug concentration measurements that are inconsistent with clinical observations or previous measurements.

The comparison between the MEIA II and the EMIT assays for tacrolimus measurement and the interference by the hematocrit were evaluated in 93 samples from routine therapeutic monitoring at tacrolimus concentrations less than 9 microg/L (group A). Additionally, the incidence of false-positive results were determined in samples (n=46) from patients who were not receiving the drug (group B). In group A, no statistical differences were observed between the mean+/-SD values obtained by MEIA II (5.14+/-2.28 microg/L) and EMIT (4.61+/-1.79 microg/L). The correlation coefficient and the regression equation (95% CI) between both assays, were 0.761 and EMIT=1.088 (0.90, 1.35) MEIA II -0.38 (-1.65, -0.46), respectively. When the samples were stratified according to the hematocrit, the median differences between the methods (MEIA II minus EMIT) were as follows: hematocritor=25%, 0.45 microg/L; hematocrit 25%-35%, 0.30 microg/L; and hematocrit35%, 0.25 microg/L (P=0.02). In group B, false-positive results (above the detection limit) were observed in 63.04% of samples analyzed by MEIA II and in 2.17% of samples analyzed by EMIT. The median differences in apparent tacrolimus results were significantly higher in the samples with the lowest hematocrit: 2.2 microg/L, 1.4 microg/L, and 0.0 microg/L in samples with hematocritor=25%, 25%-35%, and35%, respectively. In conclusion, the differences in the tacrolimus results obtained by MEIA and EMIT assays were higher in samples from patients with hematocrit less than 25%, and the MEIA assay demonstrated a high incidence of false-positive results.

A short review of the metabolism of psychoactive drugs and the pharmacogenetic factors regulating the enzymes involved is presented here. The potential clinical usefulness of phenotyping and genotyping individuals, with regard to their drug metabolic capacity, is discussed. Indications for genotyping CYP2D6 and a flow scheme for the combined use of conventional therapeutic drug monitoring (TDM) and pharmacogenetic methods for optimizing dosage-schedules of psychoactive drugs are suggested.

Amikacin and tobramycin are aminoglycosides used to treat severe Gram-negative infections. Therapeutic monitoring of both drugs is essential to avoid drug toxicity. Fluorescence polarization immunoassay kits for both amikacin and tobramycin are available from Abbott Laboratories, and assays can be run using the TDx analyzer. The test code for amikacin is 3, whereas the test code for tobramycin is 2. Here the authors report that when the operator mistakenly programmed test code 3 (amikacin code) while using the tobramycin kit, the tobramycin values were falsely elevated. The instrument software does not have any mechanism to detect this error. Similarly, when the amikacin kit was used and the operator mistakenly programmed test code 2 (tobramycin code), the amikacin values were falsely lowered. For example, in a serum sample taken from a patient the true amikacin concentration was 20.9 microg/mL. When the amikacin kit was used correctly but test code 2 was programmed, the observed concentration was falsely lowered to 6.1 microg/mL. Similarly, in another specimen the true tobramycin concentration was 3.1 microg/mL. However, when the tobramycin kit was used correctly but test code 3 was used, the observed concentration was falsely elevated to 14.3 microg/mL. The authors also observed a similar effect with controls and spiked specimens containing either amikacin or tobramycin. They conclude that correct programming of the test code is vital to obtaining useful results in amikacin and tobramycin analysis using the TDx analyzer.

Therapeutic drug monitoring has been an integral part of the clinical investigations of cyclosporin G (OG37-325 CsG), an analogue of cyclosporin A (CsA). In general, analytic approaches used for monitoring of CsA have been used for the measurement of CsG. However, the validity of this approach may be questioned, as there are significant differences between the two drugs in the areas of blood distribution, pharmacokinetics, steady-state concentration of metabolites, and biases with the various immunoassays adapted for measurement of the drug. Based on the above, it is not appropriate to assume that the therapeutic drug monitoring protocols previously established for CsA are applicable to CsG. The latter drug should be treated as a new compound, with the development of independent therapeutic monitoring guidelines. Similar approaches should be used for other immunosuppressive drugs.

Cyclosporine-G (CsG) (OG37-325) an analogue of cyclosporine-A (CsA) is presently undergoing clinical trials. As therapeutic monitoring of CsG was an integral part of these evaluations, the performance of laboratories measuring the drug was assessed through an external quality assurance program, which included all North American centers participating in the trials. The assays used by participating centers were high-performance liquid chromatography (HPLC) (n = 3), radioimmunoassay (RIA) (n = 5), and fluorescence polarization immunoassay (FPIA) (n = 24). The latter two assays, developed for measurement of CsA, were adapted for measurement of CsG. The FPIA was the most precise, with the largest proportion of laboratories reporting coefficients of variation (CNs) of10%. RIA was the least accurate method, with approximately 74% of results differing by20% from target values. FPIA and RIA methods exhibited mean recoveries of CsG of 112 and 129%, respectively. The ranking of the specificity of the assays from measurement of parent drug was HPLCRIAFPIA. FPIA and RIA produced values that were, on average, approximately 60% higher than those reported by HPLC in pooled whole blood specimens obtained from renal transplant patients. It is recommended that if CsG is approved for routine clinical use, then assays developed specifically for measurement of the drug be used.

Analysis of desmethylmethsuximide by high-performance liquid chromatography (HPLC) is described. After adding an internal standard (IS), 200 microliters of plasma was buffered to pH 4.5 and extracted with dichloroethane. The organic solvent was then evaporated to dryness and the residue reconstituted in 100 microliters of mobile phase prior to injecting a 20 microliters aliquot onto a Hypersil 5 MOS column, which was eluted with acetonitrile/acetate buffer (pH 5.5) 36:64 vol/vol. Constituents were separated in approximately 8 min. Using this method, down to 1.0 mg/L of desmethylmethsuximide in plasma can be accurately determined. The method is suitable for therapeutic monitoring of desmethylmethsuximide in patient samples.

A method of therapeutic monitoring of cyclosporine by using area under the curve (AUC) has been previously proposed. However, different mathematical methods of calculating AUC may produce different results. We compared three methods of calculating whole blood 12-h AUC of cyclosporine A (CsA) at steady state in 16 pediatric renal allograft recipients. The linear trapezoidal method tended to significantly overestimate AUC when compared with a method combining linear and log trapezoidal methods, or the Lagrange technique combined with the logarithmic trapezoidal method, producing mean differences of 13.8 ng * h/ml [95% confidence interval (CI), 7.3-20.3] and 12.8 ng * h/ml [95% CI, 7.3-18.3], respectively. However, these differences appear to be of little clinical significance because they comprised

This laboratory has developed a simple and efficient solid-phase extraction method that is combined with a high-performance liquid chromatographic method for rapid and precise therapeutic monitoring of haloperidol (Haldol) blood levels. The solid-phase extraction utilizes a mixed bed column. Sensitivity of the chromatographic method is 0.5 ng/ml (1.3 nM) of drug in serum, and separations can be performed in a 15-min chromatographic run. Advantages of this approach include enhanced speed, sensitivity, and efficiency. A high level of sensitivity may be achieved because of the absence of interferences from other drugs, metabolites, or serum components.

The analysis of clobazam and its metabolite desmethylclobazam by high-performance liquid chromatography is described. After adding an internal standard 500 microliters of plasma is extracted under basic conditions into dichloroethane. The organic solvent is then evaporated to dryness and the residue reconstituted in 100 microliters of mobile phase prior to injecting an aliquot (30 microliters) onto a Hypersil 5 MOS column, which is eluted with acetonitrile/acetate buffer (pH 5.4) 40:60 vol/vol. The components are separated in approximately 12 min. Using this method, 15 micrograms L-1 of clobazam and 30 micrograms L-1 of desmethylclobazam can be detected. The method is suitable for the therapeutic monitoring of these two drugs in patient samples.

The total concentration of ethosuximide varied between 80 and 770 mumol/L in plasma samples obtained from 33 patients on long-term treatment with the racemic drug. The ratios between the two enantiomers measured by chiral gas chromatography in the same samples were close to unity (mean +/- SD = 1.06 +/- 0.14; range = 0.76-1.39). This suggests that the disposition of ethosuximide in humans is not stereoselective and that the measurement of total concentrations of ethosuximide is sufficient for therapeutic monitoring.

Accessing patient's veins for drug level sampling is not always feasible. The use of capillary sampling techniques is often utilized when venous access is hampered. In the therapeutic monitoring of patients, unexpected drug level results often occur that can be caused by a number of different factors. The possibility that differences in assay results might occur if samples were collected by capillary stick vs. venous phlebotomy was examined by simultaneous sampling in 18 patients. Although correlation was very high (0.999) and percentage differences fairly low (range of 0 to 15.4%), a statistical difference was noted in the sampling methods. The precision was 6.5 +/- 6.58% and there was a slight negative bias (-3.76%), with capillary samples less than venous samples. Although there were statistical differences for the drugs studied in the concentration ranges evaluated, capillary samples should provide fairly small errors when compared to venous samples.

Summary A new method of measuring flupentixol in plasma was developed using gas chromatography (GC) with a nitrogen-phosphorus detector. The minimal quantifiable concentration was 0.5 ng/ml and the day-to-day coefficient of variation was 9.4% at 2 ng/ml. A comparison of flupentixol concentrations measured with radioimmunoassay (RIA) and GC was undertaken on 100 plasma samples obtained from 50 schizophrenic patients. The RIA method tended to overestimate flupentixol concentrations compared with GC. The reasons for this discrepancy might be the presence in plasma of the inactive trans(E)-flupentixol isomer and metabolites of flupentixol, which would cross-react with the antibody. The results of this study show that GC can be used for therapeutic monitoring of flupentixol.

The performance of the fluorescence polarization immunoassay (FPIA) was compared with that of a microbiological assay for the measurement of serum gentamicin concentrations. Within-run precision from duplicate assays of two concentrations (4 and 8 micrograms/ml) using FPIA and the microbiological assay yielded coefficients of variation (r) of 2.62%, 1.76% (n = 12) and 8.06%, 6.87% (n = 12), respectively. Day-to-day precision was estimated by repetitive analysis of 4 and 8 micrograms/ml control samples over a 3-week period. Coefficients of variation (r) were 2.57%, 3.09% (n = 8) and 10.71%, 14.20% (n = 8) for FPIA and the microbiological assay, respectively. Linear regression analysis performed on data from parallel determinations on 143 patient samples by the two methods showed correlations in the order of 0.74. The FPIA offers a rapid, efficient, and accurate system for therapeutic monitoring of gentamicin serum levels.

Chlorpromazine (CPZ), chlorpromazine sulfoxide (CPZSO), and chlorpromazine N-oxide (CPZNO) were each incubated (37 degrees C), for various timed intervals up to 60 min, with pooled human whole blood. Plasma and red blood cells were then separated and analyzed by a high performance liquid chromatographic method that avoids the use of alkaline extraction procedures. It was found that CPZ, CPZSO, and CPZNO were remarkably stable in whole blood under physiological conditions. CPZ was converted into CPZSO to a small extent (1%). Reports of 15-50% conversion of CPZ into CPZSO are largely due to artifacts, which result when red blood cell materials come into contact with alkali. CPZNO was recovered (85%) unchanged from the plasma. A small portion (1%) of the CPZNO was reduced to CPZ in the red blood cells. Thus, on the basis of these in vitro data, blood does not appear to be an important tissue for the metabolism of CPZ, CPZSO, or CPZNO.

The reliability of the newly developed enzyme multiplied immunoassay technique (EMIT) for gentamicin with a radioimmunoassay (RIA) technique that utilizes a double antibody technique was compared. A split sample comparison was performed on 86 serum gentamicin levels from 35 patients. The Gilford System 4 and the Abbott Auto Log Gamma Counter were employed for the EMIT and RIA assays, respectively. Comparison of the two methods revealed good correlation (r = 0.954), slope (0.952), and an intercept of 0.017 over the range of the standard curve (1--16 microgram/ml). Within-run and between-run precision were comparable for both systems. Both assays have found widespread application for routine therapeutic monitoring of gentamicin. However, the EMIT gentamicin assay offers significant advantages in speed and simplicity while maintaining comparable accuracy and precision to that of the established RIA procedures.

A brief review of the literature surrounding the relationship between plasma levels of tricyclic antidepressants currently available in the United States and clinical efficacy is presented. While therapeutic ranges for plasma levels of some tricyclic antidepressants are reasonably well established, the relationships between plasma levels of others and clinical efficacy require further clarification. Conditions under which plasma level measurements are clinically useful and factors that alter steady-state plasma levels are discussed.

Valproic acid, a new type of antiepileptic drug, has developed into one of the drugs of first choice in all types of epilepsy with the exception of infantile spasms and partial seizures. Due to its short biological half-life, a steady-state plasma concentration will be reached rapidly after initiation of therapy. However, no direct relationship between this plasma concentration and the clinical effect can be found. In autoradiography experiments, brain distribution appears to change with time, suggesting a gradual accumulation of the drug or its metabolites in certain brain areas. Two metabolites are detected in monkey and human blood plasma. Valprolactone is also found in brain tissue, but the substance is rapidly eliminated. beta, gamma-Unsaturated valproic acid has the longest half-life and is found in concentrations that can be quantitated by routine gas chromatographic analysis. The therapeutic effect appears to correlate better with dosage per kilogram body weight than with the actual plasma concentrations. Routine monitoring of valproate plasma concentrations in epileptic patients seems to be of limited value.

A rapid and simple analytical method is described for the determination of clonazepam in plasma using electron capture gas chromatography. Following a single microextraction with 100 microliter of toluene from 200-500 microliter of plasma, clonazepam is quantitated on a SP-2250 column with desmethyldiazepam as internal standard. There is no interference from endogenous substrates, clonazepam metabolites, or other commonly used antiepileptics. The lowest detectable clonazepam concentration by this method is about 1 ng/ml of plasma, which is sufficiently sensitive for both therapeutic monitoring of plasma levels and pharmacokinetic evaluation in patients and experimental animals.

A rapid and simple analytical method is described for the determination of tocainide in serum using flame ionization capillary gas chromatography. Following a single extraction with chloroform, tocainide is quantitated on an OV-17 bonded fused silica column, utilizing orphenadrine as internal standard. No interference was detected from endogenous substrates, tocainide metabolites, or other commonly used antiarrhythmic drugs. The lowest detectable tocainide concentration by this method is approximately 0.2 mg/L of serum, which is sufficiently sensitive for therapeutic monitoring. Utilizing temperature programming, this method for tocainide is applicable for several antiarrhythmic drugs.

While the correlation between plasma levels of some tricyclic antidepressants and therapeutic efficacy is well documented and the value of tricyclic antidepressant plasma level measurements is reasonably well established, the sources of error in the collection and analysis of specimens are not generally known and understood. An outline of the factors affecting the interpretation and utilization of plasma level measurements and the procedures needed to insure the accuracy and precision of tricyclic antidepressant plasma level determinations is presented. Problems facing the clinical laboratory attempting to set up a quality-control program for its tricyclic antidepressant analyses are also discussed.