Systematic Isolation and Structure Elucidation of Urinary Metabolites Optimized for the Analytical-Scale Molecular Profiling Laboratory.

Annotation and identification of metabolite biomarkers is critical for their biological interpretation in metabolic phenotyping studies, presenting a significant bottleneck in the successful implementation of untargeted metabolomics. Here, a systematic multistep protocol was developed for the purification and de novo structural elucidation of urinary metabolites. The protocol is most suited for instances where structure elucidation and metabolite annotation are critical for the downstream biological interpretation of metabolic phenotyping studies. First, a bulk urine pool was desalted using ion-exchange resins enabling large-scale fractionation using precise iterations of analytical scale chromatography. Primary urine fractions were collected and assembled into a "fraction bank" suitable for long-term laboratory storage. Secondary and tertiary fractionations exploited differences in selectivity across a range of reversed-phase chemistries, achieving the purification of metabolites of interest yielding an amount of material suitable for chemical characterization. To exemplify the application of the systematic workflow in a diverse set of cases, four metabolites with a range of physicochemical properties were selected and purified from urine and subjected to chemical formula and structure elucidation by respective magnetic resonance mass spectrometry (MRMS) and NMR analyses. Their structures were fully assigned as tetrahydropentoxyline, indole-3-acetic-acid-O-glucuronide, p-cresol glucuronide, and pregnanediol-3-glucuronide. Unused effluent was collected, dried, and returned to the fraction bank, demonstrating the viability of the system for repeat use in metabolite annotation with a high degree of efficiency.

In silico (computed) modelling of doses and dosing regimens associated with morphine levels above international legal driving limits.

BACKGROUND: Morphine can cause central nervous system side effects which impair driving skills. The legal blood morphine concentration limit for driving is 20 µg/L in France/Poland/Netherlands and 80 µg/L in England/Wales. There is no guidance as to the morphine dose leading to this concentration. AIM: The in silico (computed) relationship of oral morphine dose and plasma concentration was modelled to provide dose estimates for a morphine plasma concentration above 20 and 80 µg/L in different patient groups. DESIGN: A dose-concentration model for different genders, ages and oral morphine formulations, validated against clinical pharmacokinetic data, was generated using Simcyp®, a population-based pharmacokinetic simulator. SETTING/PARTICIPANTS: Healthy Northern European population parameters were used with age, gender and renal function being varied in the different simulation groups. In total, 36,000 simulated human subjects (100 per modelled group of different ages and gender) received repeated simulated morphine dosing with modified-release or immediate-release formulations. RESULTS: Older age, women, modified-release formulation and worse renal function were associated with higher plasma concentrations. Across all groups, morphine doses below 20 mg/day were unlikely to result in a morphine plasma concentration above 20 µg/L; this was 80 mg/day with the 80 µg/L limit. CONCLUSION: This novel study provides predictions of the in silico (computed) dose-concentration relationship for international application. Individualised morphine prescribing decisions by clinicians must be informed by clinical judgement considering the individual patient's level of impairment and insight irrespective of the blood morphine concentration as people who have impaired driving will be breaking the law. Taking into account expected morphine concentrations enables improved individualised decision making.

Development and Application of Ultra-Performance Liquid Chromatography-TOF MS for Precision Large Scale Urinary Metabolic Phenotyping.

To better understand the molecular mechanisms underpinning physiological variation in human populations, metabolic phenotyping approaches are increasingly being applied to studies involving hundreds and thousands of biofluid samples. Hyphenated ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) has become a fundamental tool for this purpose. However, the seemingly inevitable need to analyze large studies in multiple analytical batches for UPLC-MS analysis poses a challenge to data quality which has been recognized in the field. Herein, we describe in detail a fit-for-purpose UPLC-MS platform, method set, and sample analysis workflow, capable of sustained analysis on an industrial scale and allowing batch-free operation for large studies. Using complementary reversed-phase chromatography (RPC) and hydrophilic interaction liquid chromatography (HILIC) together with high resolution orthogonal acceleration time-of-flight mass spectrometry (oaTOF-MS), exceptional measurement precision is exemplified with independent epidemiological sample sets of approximately 650 and 1000 participant samples. Evaluation of molecular reference targets in repeated injections of pooled quality control (QC) samples distributed throughout each experiment demonstrates a mean retention time relative standard deviation (RSD) of <0.3% across all assays in both studies and a mean peak area RSD of <15% in the raw data. To more globally assess the quality of the profiling data, untargeted feature extraction was performed followed by data filtration according to feature intensity response to QC sample dilution. Analysis of the remaining features within the repeated QC sample measurements demonstrated median peak area RSD values of <20% for the RPC assays and <25% for the HILIC assays. These values represent the quality of the raw data, as no normalization or feature-specific intensity correction was applied. While the data in each experiment was acquired in a single continuous batch, instances of minor time-dependent intensity drift were observed, highlighting the utility of data correction techniques despite reducing the dependency on them for generating high quality data. These results demonstrate that the platform and methodology presented herein is fit-for-use in large scale metabolic phenotyping studies, challenging the assertion that such screening is inherently limited by batch effects. Details of the pipeline used to generate high quality raw data and mitigate the need for batch correction are provided.

Synthesis and biological evaluation of [(18)F]tetrafluoroborate: a PET imaging agent for thyroid disease and reporter gene imaging of the sodium/iodide symporter.

PURPOSE: The human sodium/iodide symporter (hNIS) is a well-established target in thyroid disease and reporter gene imaging using gamma emitters (123)I-iodide, (131)I-iodide and (99m)Tc-pertechnetate. However, no PET imaging agent is routinely available. The aim of this study was to prepare and evaluate (18)F-labelled tetrafluoroborate ([(18)F]TFB) for PET imaging of hNIS. METHODS: [(18)F]TFB was prepared by isotopic exchange of BF (4) (-) with [(18)F]fluoride in hot hydrochloric acid and purified using an alumina column. Its identity, purity and stability in serum were determined by HPLC, thin-layer chromatography (TLC) and mass spectrometry. Its interaction with NIS was assessed in vitro using FRTL-5 rat thyroid cells, with and without stimulation by thyroid-stimulating hormone (TSH), in the presence and absence of perchlorate. Biodistribution and PET imaging studies were performed using BALB/c mice, with and without perchlorate inhibition. RESULTS: [(18)F]TFB was readily prepared with specific activity of 10 GBq/mg. It showed rapid accumulation in FRTL-5 cells that was stimulated by TSH and inhibited by perchlorate, and rapid specific accumulation in vivo in thyroid (SUV = 72 after 1 h) and stomach that was inhibited 95% by perchlorate. CONCLUSION: [(18)F]TFB is an easily prepared PET imaging agent for rodent NIS and should be evaluated for hNIS PET imaging in humans.

Improvement in survival after paraquat ingestion following introduction of a new formulation in Sri Lanka.

BACKGROUND: Pesticide ingestion is a common method of self-harm in the rural developing world. In an attempt to reduce the high case fatality seen with the herbicide paraquat, a novel formulation (INTEON) has been developed containing an increased emetic concentration, a purgative, and an alginate that forms a gel under the acid conditions of the stomach, potentially slowing the absorption of paraquat and giving the emetic more time to be effective. We compared the outcome of paraquat self-poisoning with the standard formulation against the new INTEON formulation following its introduction into Sri Lanka. METHODS AND FINDINGS: Clinical data were prospectively collected on 586 patients with paraquat ingestion presenting to nine large hospitals across Sri Lanka with survival to 3 mo as the primary outcome. The identity of the formulation ingested after October 2004 was confirmed by assay of blood or urine samples for a marker compound present in INTEON. The proportion of known survivors increased from 76/297 with the standard formulation to 103/289 with INTEON ingestion, and estimated 3-mo survival improved from 27.1% to 36.7% (difference 9.5%; 95% confidence interval [CI] 2.0%-17.1%; p = 0.002, log rank test). Cox proportional hazards regression analyses showed an approximately 2-fold reduction in toxicity for INTEON compared to standard formulation. A higher proportion of patients ingesting INTEON vomited within 15 min (38% with the original formulation to 55% with INTEON, p < 0.001). Median survival time increased from 2.3 d (95% CI 1.2-3.4 d) with the standard formulation to 6.9 d (95% CI 3.3-10.7 d) with INTEON ingestion (p = 0.002, log rank test); however, in patients who did not survive there was a comparatively smaller increase in median time to death from 0.9 d (interquartile range [IQR] 0.5-3.4) to 1.5 d (IQR 0.5-5.5); p = 0.02. CONCLUSIONS: The survey has shown that INTEON technology significantly reduces the mortality of patients following paraquat ingestion and increases survival time, most likely by reducing absorption.

Antiepileptic drugs--best practice guidelines for therapeutic drug monitoring: a position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies.

Although no randomized studies have demonstrated a positive impact of therapeutic drug monitoring (TDM) on clinical outcome in epilepsy, evidence from nonrandomized studies and everyday clinical experience does indicate that measuring serum concentrations of old and new generation antiepileptic drugs (AEDs) can have a valuable role in guiding patient management provided that concentrations are measured with a clear indication and are interpreted critically, taking into account the whole clinical context. Situations in which AED measurements are most likely to be of benefit include (1) when a person has attained the desired clinical outcome, to establish an individual therapeutic concentration which can be used at subsequent times to assess potential causes for a change in drug response; (2) as an aid in the diagnosis of clinical toxicity; (3) to assess compliance, particularly in patients with uncontrolled seizures or breakthrough seizures; (4) to guide dosage adjustment in situations associated with increased pharmacokinetic variability (e.g., children, the elderly, patients with associated diseases, drug formulation changes); (5) when a potentially important pharmacokinetic change is anticipated (e.g., in pregnancy, or when an interacting drug is added or removed); (6) to guide dose adjustments for AEDs with dose-dependent pharmacokinetics, particularly phenytoin.

Pharmaceutical cocrystals, salts and multicomponent systems; intermolecular interactions and property based design.

As small molecule drugs become harder to develop and less cost effective for patient use, efficient strategies for their property improvement become increasingly important to global health initiatives. Improvements in the physical properties of Active Pharmaceutical Ingredients (APIs), without changes in the covalent chemistry, have long been possible through the application of binary component solids. This was first achieved through the use of pharmaceutical salts, within the last 10-15years with cocrystals and more recently coamorphous systems have also been consciously applied to this problem. In order to rationally discover the best multicomponent phase for drug development, intermolecular interactions need to be considered at all stages of the process. This review highlights the current thinking in this area and the state of the art in: pharmaceutical multicomponent phase design, the intermolecular interactions in these phases, the implications of these interactions on the material properties and the pharmacokinetics in a patient.

Rationalized Computer-Aided Design of Matrix-Metalloprotease-Selective Prodrugs.

Matrix metalloproteinases (MMPs) are central to cancer development and metastasis. They are highly active in the tumor environment and absent or inactive in normal tissues; therefore they represent viable targets for cancer drug discovery. In this study we evaluated in silico docking to develop MMP-subtype-selective tumor-activated prodrugs. Proof of principle for this therapeutic approach was demonstrated in vitro against an aggressive human glioma model, with involvement of MMPs confirmed using pharmacological inhibition.

Stabilisation of an amorphous form of ROY through a predicted co-former interaction.

The highly polymorphic compound ROY, notorious for the colour of its crystals, was the subject of an optimised high-throughput ultrasound-based co-crystal screen. This screen involved a computational pre-screen which highlighted an interaction between ROY and the potential co-former pyrogallol. We have shown that the presence of pyrogallol stabilises the amorphous form of ROY, highlighting the potential for future prediction of co-amorphous behaviours.

Tripodal tris(hydroxypyridinone) ligands for immunoconjugate PET imaging with (89)Zr(4+): comparison with desferrioxamine-B.

Due to its long half-life (78 h) and decay properties (77% electron capture, 23% ß(+), Emax = 897 keV, Eav = 397 keV, Eγ = 909 keV, Iγ = 100%) (89)Zr is an appealing radionuclide for immunoPET imaging with whole IgG antibodies. Derivatives of the siderophore desferrioxamine-B (H3DFO) are the most widely used bifunctional chelators for coordination of (89)Zr(4+) because the radiolabeling of the resulting immunoconjugates is rapid under mild conditions. (89)Zr-DFO complexes are reportedly stable in vitro but there is evidence that (89)Zr(4+) is released in vivo, and subsequently taken up by the skeleton. We have evaluated a novel tripodal tris(hydroxypyridinone) chelator, H3CP256 and its bifunctional maleimide derivative, H3YM103, for coordination of Zr(4+) and compared the NMR spectra, and the (89)Zr(4+) radiolabeling, antibody conjugation, serum stability and in vivo distribution of radiolabelled immunoconjugates with those of H3DFO and its analogues. H3CP256 coordinates (89)Zr(4+) at carrier-free concentrations forming [(89)Zr(CP256)](+). Both H3DFO and H3CP256 were efficiently radiolabelled using [(89)Zr(C2O4)4](4-) at ambient temperature in quantitative yield at pH 6-7 at millimolar concentrations of chelator. Competition experiments demonstrate that (89)Zr(4+) dissociates from [(89)Zr(DFO)](+) in the presence of one equivalent of H3CP256 (relative to H3DFO) at pH 6-7, resulting largely in [(89)Zr(CP256)](+). To assess the stability of H3DFO and H3YM103 immunoconjugates radiolabelled with (89)Zr, maleimide derivatives of the chelators were conjugated to the monoclonal antibody trastuzumab via reduced cysteine side chains. Both immunoconjugates were labelled with (89)Zr(4+) in >98% yield at high specific activities and the labeled immunoconjugates were stable in serum with respect to dissociation of the radiometal. In vivo studies in mice indicate that (89)Zr(4+) dissociates from YM103-trastuzumab with significant amounts of activity becoming associated with bones and joints (25.88 ± 0.58% ID g(-1) 7 days post-injection). In contrast, <8% ID g(-1) of (89)Zr activity becomes associated with bone in animals administered (89)Zr-DFO-trastuzumab over the course of 7 days. The tris(hydroxypyridinone) chelator, H3CP256, coordinates (89)Zr(4+) rapidly under mild conditions, but the (89)Zr-labelled immunoconjugate, (89)Zr-YM103-trastuzumab was observed to release appreciable amounts of (89)Zr(4+)in vivo, demonstrating inferior stability when compared with (89)Zr-DFO-trastuzumab. The significantly lower in vivo stability is likely to be a result of lower kinetic stability of the Zr(4+) tris(hydroxypyridinone complex) relative to that of DFO and its derivatives.

The absorption of gabapentin following high dose escalation.

Gabapentins (GBP) is structurally similar to GABA yet its mode of action remains uncertain. It is water-soluble and GI tract absorption occurs via the L-amino acid transport system in the proximal small bowel. It has been suggested that this transportation is capacity limited, thus decreasing GBP bioavailability at higher doses. GBP is not protein bound, therefore, salivary levels might be expected to be similar to those in serum; also the drug does not induce hepatic enzymes and is excreted unmetabolised by the kidney. Within the dose-range normally prescribed, it is devoid of pharmacokinetic (PK) drug interactions with all other anti-epileptic drugs. This study assesses two things in patients with epilepsy: (a) bioavailability of higher doses of GBP (1200-4800 mg per day), and (b) the influence of high dose GBP on between-dose serum concentrations of co-prescribed anti-epileptic drugs. After stabilising at each dosage, a sequence of serum and saliva samples were collected within the dosage interval; GBP and co-medication concentrations were determined and the results subjected to PK modelling. Meaned results from 10 patients indicate that GBP continues to be absorbed in a reasonably linear manner relative to dose up to 4800 mg per day. The study also shows that GBP is transported into saliva, however, salivary concentrations are only 5-10% of those in plasma. Furthermore, the results indicate that GBP, in higher than recommended doses, did not change plasma concentrations of lamotrigine, carbamazepine, carbamazepine-epoxide, vigabatrin, primidone, phenobarbitone or phenytoin when added to treatment. It is concluded that larger than recommended doses of GBP can be efficiently absorbed by some patients and also that GBP plasma levels do not fluctuate greatly between dosage intervals, therefore, twice daily dosage is a possibility.

Pharmacotherapy of the third-generation AEDs: lacosamide, retigabine and eslicarbazepine acetate.

INTRODUCTION: The search for new, more effective antiepileptic drugs (AEDs) continues. The three most recently approved drugs, the so-called third-generation AEDs, include lacosamide, retigabine and eslicarbazepine acetate and are licensed as adjunctive treatment of partial epilepsy in adults. AREAS COVERED: For the above three AEDs, their mechanisms of action, pharmacokinetic characteristics, drug-drug interactions, pharmacotherapeutics, dose and administration and therapeutic drug monitoring are reviewed in this paper. EXPERT OPINION: Lacosamide and retigabine act through novel mechanisms, while eslicarbazepine acetate, a pro-drug for eslicarbazepine, acts in a similar manner to several other AEDs. All three AEDs are associated with linear pharmacokinetic and rapid absorption and undergo metabolism. Their drug-drug interaction profile is low (lacosamide and retigabine) to modest (eslicarbazepine) in propensity. At the highest approved doses for the three AEDs, responder rates were similar. The most commonly observed adverse effects compared with placebo were dizziness, headache, diplopia and nausea for lacosamide; dizziness, somnolence and fatigue for retigabine and dizziness and somnolence for eslicarbazepine acetate. The precise role that these new AEDs will have in the treatment of epilepsy and whether they will make a significant impact on the prognosis of intractable epilepsy is not yet known and will have to await further clinical experience.

Dithiocarbamate complexes as radiopharmaceuticals for medical imaging.

Over the past 30 years dithiocarbamate ligands have found application in radiopharmaceutical metal-ligand complexes to image a range of disease states. The vast majority of research and applications, and the widest range of complex structures, have involved radionuclides of technetium and rhenium. Considering the extent of coordination chemistry of dithiocarbamate ligands described elsewhere in this issue, the extent of radiopharmaceutical application with metallic radionuclides is surprisingly narrow. Here we summarise the types of radiopharmaceutical complexes studied and the uses, and potential uses, to which they have been put in nuclear medicine.

The effect of lamotrigine on valproic acid concentrations.

PURPOSE: To determine whether lamotrigine affects serum concentrations of valproic acid. METHODS: Pre-morning-dose serum valproic acid concentrations were measured in 76 subjects with epilepsy (48 M, 28 F, age range 6-20 years, mean age 14 years) in whom lamotrigine was added while the dose of valproate and other medication remained unchanged. In a comparison group, either acetazolamide or gabapentin was added to sodium valproate. RESULTS: Far more subjects (26/76 = 34%) had an increase of >25% in valproic acid concentration with lamotrigine than those who had a decrease of >25% (4/76 = 5.3%). The mean valproic acid concentration before starting lamotrigine was 61.0 mg/L and on lamotrigine was 67.1 mg/L; the difference in means was 6.1 mg/L (standard error 2.1, 95% confidence limits 2.0, 10.2, p=0.004, highly significant, paired sample t-test, two-tailed), a rise of 10%. The change in valproic acid concentration appeared to depend on the initial valproic acid concentration (Pearson r=-0.405, p<0.001). In 14.5% of the subjects the increase in valproate concentration was >50%, which could lead to toxicity, although the increase tended to occur with lower or intermediate initial valproic acid concentrations whereas a small overall decrease in valproic acid concentrations with lamotrigine was found with the higher initial valproic acid concentrations. One subject had abnormal bruising with the increased valproate level after lamotrigine was added, which resolved on decreasing the valproate dose. The changes in valproic acid concentrations in the comparison group were small (mean increase 2.6%) and were not statistically significant. CONCLUSIONS: Although there is a wide variation in the changes of valproic acid concentrations when lamotrigine is added, the concentrations tend to increase rather than decrease, especially with low or intermediate initial valproic acid concentrations. In some cases valproate toxicity, manifested by abnormal bruising, may result, although at higher initial valproic acid concentrations the valproic acid concentration usually tends to fall slightly with the addition of lamotrigine.

Formulation changes and time trends in outcome following paraquat ingestion in Sri Lanka.

INTRODUCTION: Deliberate self-harm with pesticides is a significant public health problem in rural Asia. We have previously shown an improved survival of patients with paraquat self-poisoning following the introduction of a new formulation with an increased emetic concentration, an alginate and a purgative in Sri Lanka. Further, formulation changes were introduced in October 2006; this study was designed to assess the impact of these changes on 6-week mortality following paraquat ingestion. METHODS: Prospective, cohort study of patients admitted with paraquat poisoning to 10 hospitals across Sri Lanka between September 2006 and September 2008. RESULTS: Overall, there was a significant (p < 0.001) increase in survival in the 533 patients included in this study compared to previous data (44.5 vs. 35.2% before September 2006 and 27.1% before October 2004). Patients ingesting the new INTEON formulation had a higher survival rate than those ingesting standard formulation (40.2 vs. 31.0%), but this effect was not statistically significant in Cox's proportional hazards model (hazard ratio 0.81, 95% CI 0.61?1.08 (unadjusted) and 1.17, 95% CI 0.82?1.68 (fully adjusted), respectively). CONCLUSIONS: This study has confirmed a continued improvement in survival of patients following self-harm with paraquat in Sri Lanka in recent years; however, in contrast to previous investigations, a beneficial effect associated with the INTEON formulation could not be substantiated. This may be partly due to the large number of patients in whom paraquat concentrations were too low for analytical confirmation of the formulation (n = 105) and who had a very high survival rate (86.7%).

Efficient bifunctional gallium-68 chelators for positron emission tomography: tris(hydroxypyridinone) ligands.

A new tripodal tris(hydroxypyridinone) bifunctional chelator for gallium allows easy production of (68)Ga-labelled proteins rapidly under mild conditions in high yields at exceptionally high specific activity and low concentration.

Significant pregabalin toxicity managed with supportive care alone.

There are two previously reported cases describing the management of pregabalin self-poisoning and one further case of management of therapeutic pregabalin accumulation. The peak reported pregabalin concentrations in these cases ranged from 13 mg/L to approximately 60 mg/L. Previous case reports have suggested that both supportive care and enhanced elimination are appropriate managements for pregabalin toxicity. A 54-year-old male presented following ingestion of 8.4 g of pregabalin. Initially, he had no clinical features of toxicity, although he developed significant neurological depression and coma approximately 3 h post-ingestion. He was managed with supportive care (including endotracheal intubation and mechanical ventilation) until his level of consciousness improved. Subsequent toxicological screening confirmed isolated pregabalin ingestion, with a serum pregabalin concentration of 66.5 mg/L at the time he clinically deteriorated. The pharmacokinetic properties of pregabalin indicate the potential value of extra-corporeal elimination methods such as haemodialysis. Clinical toxicologists should be aware that whilst there is a pharmacokinetic basis for the use of extra-corporeal methods in those with severe toxicity arising from excessive plasma pregabalin concentrations, there are case reports, including this one, where patients have been managed with supportive measures only.

Sodium and bone health: impact of moderately high and low salt intakes on calcium metabolism in postmenopausal women.

High salt intake is a well-recognized risk factor for osteoporosis because it induces calciuria, but the effects of salt on calcium metabolism and the potential impact on bone health in postmenopausal women have not been fully characterized. This study investigated adaptive mechanisms in response to changes in salt and calcium intake in postmenopausal women. Eleven women completed a randomized cross-over trial consisting of four successive 5-wk periods of controlled dietary intervention, each separated by a minimum 4-wk washout. Moderately low and high calcium (518 versus 1284 mg) and salt (3.9 versus 11.2 g) diets, reflecting lower and upper intakes in postmenopausal women consuming a Western-style diet, were provided. Stable isotope labeling techniques were used to measure calcium absorption and excretion, compartmental modeling was undertaken to estimate bone calcium balance, and biomarkers of bone formation and resorption were measured in blood and urine. Moderately high salt intake (11.2 g/d) elicited a significant increase in urinary calcium excretion (p = 0.0008) and significantly affected bone calcium balance with the high calcium diet (p = 0.024). Efficiency of calcium absorption was higher after a period of moderately low calcium intake (p < 0.05) but was unaffected by salt intake. Salt was responsible for a significant change in bone calcium balance, from positive to negative, when consumed as part of a high calcium diet, but with a low calcium intake, the bone calcium balance was negative on both high and low salt diets.

Lack of an effect of topiramate on lamotrigine serum concentrations.

PURPOSE: Pharmacokinetic interactions between the older antiepileptic drugs (AEDs) and topiramate (TPM) were assessed during the clinical development of this drug. Lamotrigine (LTG) has become established as an important new drug in treating a wide spectrum of seizure types, but there are no published data on whether LTG serum concentrations change when TPM is added to treatment. METHODS: Escalating doses of TPM were added to stable LTG treatment in 24 young patients (8-21 years) with epilepsy. Blood samples taken before the morning dose were collected for drug-concentration measurement in all patients before starting treatment with TPM and after stabilisation at each dose escalation. Several patients had been maintained on unchanged therapy with drug-concentration monitoring for many months before introducing TPM, and a sequence of baseline LTG serum concentrations were available on these patients. RESULTS: The mean of all baseline LTG concentrations for the group as a whole was 10.4 +/- 4.4 mg/L compared with 9.7 +/- 4.3 mg/L after addition of TPM. A comparison of last baseline LTG concentration with first test LTG concentration (i.e., after 2 weeks' TPM treatment) gave mean values of 10.7 +/- 4.7 and 10.8 +/- 4.6 mg/L, respectively. The mean LTG concentration for patients while taking their highest TPM dose was 9.5 +/- 4.3 mg/L. The analysis-of-variance modeling for the effect of TPM on LTG concentration yielded a mean LTG concentration ratio (with TPM vs. without TPM) of 94.2%, with a 90% confidence interval of 89.5-99.1%. CONCLUSIONS: TPM did not cause a significant change in LTG serum concentration in this group of patients.

Therapeutic drug monitoring of the newer antiepileptic drugs.

The aim of the present review is to discuss the potential value of therapeutic drug monitoring (TDM) of the newer antiepileptic drugs (AEDs) felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin, and zonisamide. Studies of the relationship between serum concentrations and clinical efficacy of these drugs are reviewed, and the potential value of TDM of the drugs is discussed based on their pharmacokinetic properties and mode of action. Analytical methods for the determination of the serum concentrations of these drugs are also briefly described. There are only some prospective data on the serum concentration-effect relationships, and few studies have been designed primarily to study these relationships. As TDM is not widely practiced for the newer AEDs, there are no generally accepted target ranges for any of these drugs, and for most a wide range in serum concentration is associated with clinical efficacy. Furthermore, a considerable overlap in drug concentrations related to toxicity and nonresponse is reported. Nevertheless, the current tentative target ranges for felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine (10-hydroxy-carbazepine metabolite), tiagabine, topiramate, vigabatrin, and zonisamide are 125 to 250 micromol/L, 70 to 120 micromol/L, 10 to 60 micromol/L, 35 to 120 micromol/L, 50 to 140 micomol/L, 50 to 250 nmol/L, 15 to 60 micromol/L, 6 to 278 micromol/L, and 45 to 180 micromol/L, respectively. Further systematic studies designed specifically to evaluate concentration-effect relationships of the new AEDs are urgently needed. Although routine monitoring in general cannot be recommended at present, measurements of some of the drugs is undoubtedly of help with individualization of treatment in selected cases in a particular clinical setting.