Inter- and intra-subject variability in gabapentin absorption and absolute bioavailability

Interactions between antiseizure medications and foods and drinks: A systematic review

Antiseizure medications (ASMs) constitute the principal of treatment for patients with epilepsy, where long-term treatment is usually necessary. The purpose of this systematic review is to provide practical and useful information regarding various aspects of the interactions between ASMs and foods and drinks. MEDLINE and ScienceDirect, from the inception to July 15, 2023, were searched for related publications. In both electronic databases, the following search strategy was applied, and the following keywords were used (in title/abstract): "food OR drink" AND "antiepileptic OR antiseizure." The primary search yielded 738 studies. After implementing our inclusion and exclusion criteria, we could identify 19 studies on the issue of interest for our endeavor. Four studies were identified in the recheck process and not by the primary search. All studies provided low level of evidence. Interactions between foods and ASMs are a common phenomenon. Many factors may play a role for such an interaction to come to play; these include drug properties, administration route, and administration schedule, among others. Drugs-foods (-drinks) interactions may change the drug exposure or plasma levels of drugs (e.g., grapefruit juice increases carbamazepine concentrations and the bioavailability of cannabidiol is increased 4-5 folds with concomitant intake of fat-rich food); this may require dosage adjustments. Interactions between ASMs and foods and drinks may be important. This should be taken seriously into consideration when consulting patients and their caregivers about ASMs. Future well-designed investigations should explore the specific interactions between foods (and drinks) and ASMs to clarify whether they are clinically important. PLAIN LANGUAGE SUMMARY: Interactions between antiseizure medications and foods and drinks may be important. This should be taken into consideration in patients with epilepsy.

A comprehensive update on the ADMET considerations for α2δ calcium channel ligand medications for treating restless legs syndrome

INTRODUCTION

Restless legs syndrome/Willis-Ekbom disease (RLS/WED) is a sleep-related sensory-motor disorder associated with poor sleep quality and impaired daily functioning. In patients affected by chronic RLS/WED, a pharmacological therapy is recommended. International guidelines suggest to start the treatment with a α2δ calcium channel ligand in most cases, unless contraindicated.

AREAS COVERED

The present review is based on an extensive Internet and PubMed search from 1986 to 2024. Our purpose is to describe the absorption, distribution, metabolism, and toxicology (ADMET) of the α2δ ligands, with common consideration for the therapeutic class, specificities of different compounds, efficacy, and safety in relation to other treatment options.

EXPERT OPINION

α2δ ligands are quite similar in their ADMET profiles, sharing most of the pharmacokinetics and potential adverse effects. However, we highlight the linear kinetic of gabapentin enacarbil and pregabalin, differently from gabapentin. α2δ ligands are safe and effective for the treatment of RLS/WED. Additional benefits can be obtained in comorbid insomnia, chronic pain syndromes, history of impulse control disorder, and comorbid anxiety. The use of α2δ ligands is associated with poor risk of augmentation. We still need new long-term safe and effective treatments, which could be developed along with our knowledge of RLS/WED pathophysiology.

Effects of Gabapentin and Pregabalin on Calcium Homeostasis: Implications for Physical Rehabilitation of Musculoskeletal Tissues

PURPOSE OF REVIEW

In this review, we discuss the mechanism of action of gabapentinoids and the potential consequences of long-term treatment with these drugs on the musculoskeletal system.

RECENT FINDINGS

Gabapentinoids, such as gabapentin (GBP) and pregabalin (PGB) were designed as antiepileptic reagents and are now commonly used as first-line treatment for neuropathic pain and increasingly prescribed off-label for other pain disorders such as migraines and back pain. GBP and PGB exert their analgesic actions by selectively binding the α₂δ₁ auxiliary subunit of voltage-sensitive calcium channels, thereby inhibiting channel function. Numerous tissues express the α₂δ₁ subunit where GBP and PGB can alter calcium-mediated signaling events. In tissues such as bone, muscle, and cartilage, α₂δ₁ has important roles in skeletal formation, mechanosensation, and normal tissue function/repair that may be affected by chronic use of gabapentinoids. Long-term use of gabapentinoids is associated with detrimental musculoskeletal outcomes, including increased fracture risk. Therefore, understanding potential complications is essential for clinicians to guide appropriate treatments.

Enhanced assessment of human dynamic stability by eliminating the effect of body height: modeling and experiment study

Margin of stability (MOS) is one of the essential indices for evaluating dynamic stability. However, there are indications that MOS was affected by body height and its application in identifying factors on dynamic stability other than body height is restricted. An inverted pendulum model was used to simulate human walking and investigate the relevance between MOS and body height. Eventually, a height-independent index in dynamic stability assessment (named as Angled Margin of Stability, AMOS) was proposed. For testing, fifteen healthy young volunteers performed walking trials with normal arm swing, holding arms, and anti-normal arm swing. Kinematic parameters were recorded using a gait analysis system with a Microsoft Kinect V2.0 and instrumented walkway. Both simulation and test results show that MOS had a significant correlation with height during walking with normal arm swing, while AMOS had no such significant correlation. Walking with normal arm swing produced significantly larger AMOS than holding arms and anti-normal arm swing. However, no significant difference showed up in MOS between normal arm swing and holding arms. The results suggest that AMOS is not affected by body height and has the potential to identify the variations in dynamic stability caused by physiological factors other than body height.

Interindividual Variability in the Bioavailability of Gabapentin Enacarbil Extended Release in Healthy Adults: An Analysis of Data From 6 Phase I Studies

BACKGROUND

The absorption and bioavailability of oral gabapentin are associated with a high degree of interindividual variability. Gabapentin enacarbil, a prodrug of gabapentin, is well absorbed and provides sustained, dose-proportional exposure to gabapentin. The aim of this analysis was to describe the interindividual variability in the bioavailability of gabapentin after gabapentin enacarbil administration in healthy subjects.

METHODS

Gabapentin pharmacokinetic (PK) parameters after an oral dose of gabapentin enacarbil 1200 mg (2 600-mg tablets) were compared across 6 phase I studies in healthy adults (n = 12 per study). The distribution of bioavailability values was assessed in all studies.

RESULTS

The mean PK parameters of gabapentin were consistent across the trials: maximum concentration range: 6.4-7.9 μg/mL, time to maximum concentration range: 5.2-8.2 hours, area under the plasma-concentration curve extrapolated from time 0 to infinity or at steady state range: 70.8-109.4 μg·h/mL, and bioavailability range: 64.8%-82.9%. Overall, the mean bioavailability was 74.1% (SD, 14.1; coefficient of variation, 19.1%). Individual bioavailability across all studies ranged from 42% to 100%.

CONCLUSIONS

Gabapentin PK after gabapentin enacarbil administration was consistent across studies, with low interindividual variability in bioavailability. Gabapentin enacarbil may provide more consistent and predictable exposure to gabapentin than oral gabapentin formulations.

Seizure-like behaviour in antelope ground squirrels

In a colony of 52 antelope ground squirrels conceived in the wild and raised in the laboratory, 42% of adult animals exhibited freezing and seizure-like behaviour in response to the minor stress of monthly cage changes. This behavioural pattern, which was never exhibited at other times, is similar to that previously described in Mongolian gerbils. Characteristics of the behavioural pattern do not seem to be indicative of a captivity-induced stereotypy.

Extracorporeal Treatment for Gabapentin and Pregabalin Poisoning: Systematic Review and Recommendations From the EXTRIP Workgroup

Toxicity from gabapentin and pregabalin overdose is commonly encountered. Treatment is supportive, and the use of extracorporeal treatments (ECTRs) is controversial. The EXTRIP workgroup conducted systematic reviews of the literature and summarized findings following published methods. Thirty-three articles (30 patient reports and 3 pharmacokinetic studies) met the inclusion criteria. High gabapentinoid extracorporeal clearance (>150mL/min) and short elimination half-life (<5 hours) were reported with hemodialysis. The workgroup assessed gabapentin and pregabalin as "dialyzable" for patients with decreased kidney function (quality of the evidence grade as A and B, respectively). Limited clinical data were available (24 patients with gabapentin toxicity and 7 with pregabalin toxicity received ECTR). Severe toxicity, mortality, and sequelae were rare in cases receiving ECTR and in historical controls receiving standard care alone. No clear clinical benefit from ECTR could be identified although major knowledge gaps were acknowledged, as well as costs and harms of ECTR. The EXTRIP workgroup suggests against performing ECTR in addition to standard care rather than standard care alone (weak recommendation, very low quality of evidence) for gabapentinoid poisoning in patients with normal kidney function. If decreased kidney function and coma requiring mechanical ventilation are present, the workgroup suggests performing ECTR in addition to standard care (weak recommendation, very low quality of evidence).

Derivatization of γ-Amino Butyric Acid Analogues for Their Determination in the Biological Samples and Pharmaceutical Preparations: A Comprehensive Review

γ-Aminobutyric acid (GABA) plays an important role in regulating neuronal excitability. Four structurally related drugs to GABA including pregabalin (PGB), gabapentin (GBP), vigabatrin (VGB), and baclofen are used for the treatment of central nervous system disorders. These drugs are small aliphatic molecules having neither fluorescent nor strong absorbance in the ultraviolet/visible region; therefore, direct determination of these analytes by optical methods is difficult. Additionally, their high boiling point makes gas chromatography impossible. Accordingly, the amine or acid moiety in these drugs is derivatized in order to improve their selectivity and sensitivity during determination in the biological samples. This review focuses on derivatization based methods and their different reactions for determination of PGB, GBP, VGB, and baclofen in the biological samples and pharmaceutical preparations reported between 1980 and 2020. High-performance liquid chromatography methods coupled with different detectors are a commonly used methods for determination of GABA analogs after derivatization. These methods cover 38.89% of all developed methods for determination of GABA analogs.

Strategies for Rotation between Gabapentinoids in the Inpatient Setting

Guidance and evidence to support best practices in rotating between gabapentinoids is lacking. This retrospective cohort study was performed to describe and evaluate strategies for rotation. Patients rotated while admitted from June 1st, 2014 to April 25th, 2020 at a large, academic medical center were included. The primary outcome was the proportion of rotations using a direct switch strategy compared to a cross-taper strategy. Secondary outcomes were successful rotation, defined as stable or improved pain scores pre- to post-rotation, dose ratios, and adverse effects. A total of 67 patients were included. Median age was 50 years (35 - 59) and 58% (38) were male. The majority used a direct switch strategy (87%). Ninety-five percent of patients using the direct switch strategy and 78% of patients using the cross-taper strategy were successful. There was no difference in strategies between those who were successful and those who were not. Post hoc analysis of patients with normal renal function (eGFR ≥ 50 mL/min/1.73 m²) found that those who were successful were more likely to have used a direct switch strategy (p = 0.048). There were no differences in adverse effects. These findings suggest that either strategy is reasonable for gabapentinoid rotation in the inpatient setting.

Gabapentin Reduces Blood Pressure and Heart Rate through the Nucleus Tractus Solitarii

Background

Oral and intravenous gabapentin can markedly attenuate blood pressure (BP) in hypertensive rats. The nucleus tractus solitarii (NTS) is the primary integrative center for cardiovascular control and other autonomic functions in the central nervous system. However, the signaling mechanisms involved in gabapentin-mediated cardiovascular effects in the NTS remain unclear. We investigated whether the nitric oxide synthase (NOS) signaling pathway was involved in gabapentin-mediated BP regulation in the NTS of spontaneously hypertensive (SHR) rats.

Methods

SHR rats were anesthetized with urethane at age 10-12 weeks. Arterial pressure and heart rate (HR) were monitored through a femoral artery catheter. For stereotaxic intra-NTS microinjection, the dorsal surface of the medulla was exposed by limited craniotomy. We observed that unilateral microinjection of gabapentin into the NTS whether to change dose-related BP and HR. Then, unilateral microinjection of gabapentin into the NTS before and after N(ω)-nitro-L-arginine methyl ester (L-NAME) treatment whether to change blood pressure and heart rate.

Results

Unilateral microinjection of gabapentin into the NTS produced prominent dose-related depressor and bradycardic effects in SHR rats. The cardiovascular effects of gabapentin were attenuated by the prior administration of the NOS inhibitor, L-NAME.

Conclusions

Gabapentin modulated central BP and HR control in the NTS of SHR rats in this study through NOS signaling.

The Effect of Once-Daily Gabapentin Extended Release Formulation in Patients With Postamputation Pain

Objectives

To compare gabapentin extended-release, a gastro-retentive formulation, in relieving postamputation pain among gabapentin-experienced and gabapentin-naïve patients.

Design

Open-labeled pilot study.

Subjects

Sixteen patients with postamputation pain (8 patients in the gabapentin-experienced and 8 patients in the gabapentin-naïve groups).

Methods

Patients were started on gabapentin extended-release and were followed up for 8 weeks. Patients reported their pain severity during rest and movement using a numeric rating scale (NRS), interference of pain with daily activities using the modified brief pain inventory (MBPI) questionnaire, and treatment satisfaction using the treatment satisfaction questionnaire for medication (TSQM).

Results

Patients from both gabapentin-experienced and gabapentin-naïve groups achieved a significant and sustainable pain relief over the course of therapy. The pain scores at rest decreased in both gabapentin-experienced and gabapentin-naïve groups from 5.88 ± 1.36 and 4.88 ± 2.95 to 1.88 ± 0.99 and 1.38 ± 1.51, respectively. An average percent of pain relief with gabapentin extended-release was noted to be significant (p < 0.01) after 8 weeks of therapy among gabapentin-experienced (81.25 ± 16.42%) and gabapentin-naïve groups (85 ± 17.73%) when compared to baseline for gabapentin-experienced (31.25 ± 29%) and gabapentin-naïve groups (36.25 ± 34.2%), respectively. Gabapentin-experienced and gabapentin-naïve groups had no significant difference in global satisfaction from treatment (79.14 ± 10.47 and 83.3 ± 20.82), convenience of treatment (73.78 ± 19.04 and 90.44 ± 11.66), effectiveness of treatment (72.6 ± 10.1 and 79.73 ± 11.6). The only statistically significant difference among gabapentin-experienced and gabapentin-naïve groups was found in adverse event tolerability (65.78 ± 10.36 and 85.8 ± 10.14, p < 0.01).

Conclusion

Once-daily dosing of gabapentin-extended release showed significant improvement in pain severity and functional status, with no difference found between gabapentin-experienced versus gabapentin-naïve patients.

Therapeutic drug monitoring of gabapentin in various indications

OBJECTIVES

Gabapentin has been increasingly used in various indications in recent years. Despite variable pharmacokinetics, therapeutic drug monitoring (TDM) is scarcely described in other indications than epilepsy. The aim of the study was to investigate the use and pharmacokinetic variability of gabapentin in epilepsy and non-epilepsy indications and to further evaluate the use of TDM in patients with restless legs syndrome (RLS).

MATERIALS & METHODS

Population-based data from the Norwegian Prescription Database, retrospective TDM data from the section for Clinical Pharmacology, the National Center for Epilepsy, Norway, and prospective observational data on patients with RLS were used.

RESULTS

The use of gabapentin increased by 30% from 2014 to 2017 (32 181 to 42 675 users). TDM data from 120 patients showed a 22-fold pharmacokinetic variability in concentration/dose ratios, and this ratio was elevated in elderly patients (≥65 years). The majority of elderly used gabapentin for non-epilepsy indications. In patients with RLS, intake in the evening/night only was common due to nocturnal symptoms, in contrast to regular dosing regimens in epilepsy. Thus, drug fasting concentrations do not reflect concentrations at the time of required therapeutic effect. TDM was still found useful in most patients to support dosage increase or evaluate adverse effects.

CONCLUSION

Due to extensive pharmacokinetic variability, TDM can benefit patients using gabapentin. Challenges with applying TDM in new indications such as RLS include different dosage regimens and consequently different interpretation of serum concentrations. Thus, TDM should be requested on clear clinical grounds and the service tailored according to the therapeutic indication.

Classification and regression of spatio-temporal signals using NeuCube and its realization on SpiNNaker neuromorphic hardware

OBJECTIVE

The objective of this work is to use the capability of spiking neural networks to capture the spatio-temporal information encoded in time-series signals and decode them without the use of hand-crafted features and vector-based learning and the realization of the spiking model on low-power neuromorphic hardware.

APPROACH

The NeuCube spiking model was used to classify different grasp movements directly from raw surface electromyography signals (sEMG), the estimations of the applied finger forces as well as the classification of two motor imagery movements from raw electroencephalography (EEG). In a parallel investigation, the designed spiking decoder was implemented on SpiNNaker neuromorphic hardware, which allows low-energy real-time processing.

MAIN RESULTS

Experimental results reveal a better classification accuracy using the NeuCube model compared to traditional machine learning methods. For sEMG classification, we reached a training accuracy of 85% and a test accuracy of 84.8%, as well as less than 19% of relative root mean square error (rRMSE) when estimating finger forces from six subjects. For the EEG classification, a mean accuracy of 75% was obtained when tested on raw EEG data from nine subjects from the existing 2b dataset from 'BCI competition IV'.

SIGNIFICANCE

This work provides a proof of concept for a successful implementation of the NeuCube spiking model on the SpiNNaker neuromorphic platform for raw sEMG and EEG decoding, which could chart a route ahead for a new generation of portable closed-loop and low-power neuroprostheses.

LC-MS/MS Quantification of Tramadol and Gabapentin Utilizing Solid Phase Extraction

An accurate, highly sensitive, and precise method for quantitative analysis of tramadol (TMD) and gabapentin (GBP) by high performance liquid chromatography and tandem mass spectrometry in human plasma was proposed and validated successfully using venlafaxine and pregabalin as internal standards (ISTDs), respectively. An aliquot of 200 μL of plasma was mixed with internal standard dilution and extraction was performed by using solid phase extraction (SPE) technique. Peak resolution was achieved on Phenomenex PFP column (50×4.6 mm, 2.6 μm). The total analytical run time was 3.8 min. Both analytes were monitored using multiple reaction monitoring (MRM) scan and the mass spectrometer was operated in positive polarity mode. The method was validated for specificity, sensitivity, precision, accuracy, and other analytical parameters. The results found were satisfactory over the linear calibration range of 1-500 ng/mL and 10-6000 ng/mL for TMD and GBP, respectively. The developed method can be ready to use by scientific community for quantification of analytes in plasma samples from various clinical studies of different dose strengths.

Pharmacokinetics of immediate release, extended release, and gastric retentive gabapentin formulations in healthy adults

Objective: Gabapentin immediate release (GBP-IR), gabapentin gastric retentive (GBP-GR), and the prodrug gabapentin enacarbil extended release formulation (GEn) have been approved for management of postherpetic neuralgia (PHN) in adults. This is the first pharmacokinetic (PK) comparison of all three formulations using FDA-recommended doses for PHN. Materials: This study compared the steady-state PK of GBP-IR 600 mg t.i.d., GBP-GR 1,800 mg q.d., and GEn 600 mg b.i.d. in healthy adults. Methods: The open-label study consisted of a 3-day lead-in of escalating doses of GBP-IR, 5 days of treatment with each formulation (GPB-IR, GPB-GR, and GEn), and a 7-day taper period on 600 mg GEn q.d.. Plasma concentrations were collected on day 5 for each formulation. PK parameters were estimated from plasma concentration data. Results: 14 healthy subjects (7 men, 7 women; mean (SD) age, 46.8 (7.60) years; mean (SD) body mass index, 26.7 (1.7) kg/m²) received all doses and completed the study. GBP-GR resulted in substantially (~ 4-fold) higher peak-to-trough ratio and percent fluctuation compared to GEn. GEn resulted in more sustained and less fluctuating daily exposure relative to GBP-IR, particularly at the end of 24 hours of dosing. In contrast, gabapentin fluctuation from GBP-IR consisted of 3 distinct peaks. After dose normalization, gabapentin exposure with GEn was ~ 2.2-fold and ~ 1.4-fold higher compared to GBP-GR and GBP-IR, respectively. All treatments were well tolerated. Conclusion: GEn requires less frequent dosing compared with GBP-IR and fluctuates less with sustained gabapentin exposure throughout the day. These PK differences may have clinically relevant implications.

Reference ranges for antiepileptic drugs revisited: a practical approach to establish national guidelines

BACKGROUND AND OBJECTIVE

Laboratories sometimes use different reference ranges for the same antiepileptic drug (AED), particularly for new and poorly investigated drugs. This may contribute to misunderstandings, concerns or inappropriate dose changes, which in turn may affect therapeutic effect, drug safety or treatment adherence. Therefore, the Norwegian Association of Clinical Pharmacology wished to update and harmonize the reference ranges for AEDs and establish national guidelines for Norway.

METHODS

A working group collected information on the reference ranges used by Norwegian laboratories for all commonly used AEDs. These reference ranges were compared to recent recommendations by the International League Against Epilepsy, current literature, applicable clinical studies, reference ranges used by leading Northern European epilepsy centers outside of Norway, and routine data derived from Norwegian laboratory databases.

RESULTS

Reference ranges varied between laboratories for four of 23 available AEDs (lamotrigine, valproate, eslicarbazepine and oxcarbazepine). For four AEDs (brivaracetam, perampanel, stiripentol and sulthiame), reference ranges had not previously been established. In total, 13 reference ranges were either harmonized, updated or newly established. No changes were applied to the remaining 10 AEDs.

CONCLUSION

Updated and harmonized reference ranges are now available for 22 of the 23 AEDs available in Norway. The exception is vigabatrin (reference range not applicable). Revision of reference ranges is an important part of pharmacovigilance of AEDs and must be a continuous process based on current literature and clinical experience.

Use of α2δ Ligands for Restless Legs Syndrome/Willis Ekbom Disease

Restless legs syndrome is a common neurological condition affecting a substantial portion of the population. It can be an idiopathic disorder, or one that is secondary to another cause. Given that the underlying pathophysiology of restless legs syndrome is not well understood, several drug classes have been studied for symptom control. While dopamine agonists have long been the mainstay of first-line treatment for restless legs syndrome, recently, the α2δ ligands have been increasingly used. These agents have proven both efficacious and safe in a number of clinical trials. Additionally, compared with the dopamine agonists, they have been associated with less augmentation, a phenomenon whereby symptoms emerge earlier in the day, become more severe, and may spread to areas of the body previously unaffected. Newer clinical guidelines for restless legs syndrome are increasingly recommending the α2δ ligands as a logical first-choice medication for patients needing drug therapy for symptom control.

Population pharmacokinetics of gabapentin in healthy Korean subjects with influence of genetic polymorphisms of ABCB1

The objective of this study was to perform population pharmacokinetic (PK) analysis of gabapentin in healthy Korean subjects and to investigate the possible effect of genetic polymorphisms (1236C > T, 2677G > T/A, and 3435C > T) of ABCB1 gene on PK parameters of gabapentin. Data were collected from bioequivalence studies, in which 173 subjects orally received three different doses of gabapentin (300, 400, and 800 mg). Only data from reference formulation were used. Population pharmacokinetics (PKs) of gabapentin was estimated using a nonlinear mixed-effects model (NONMEM). Gabapentin showed considerable inter-individual variability (from 5.2- to 8.7-fold) in PK parameters. Serum concentration of gabapentin was well fitted by a one-compartment model with first-order absorption and lag time. An inhibitory Emax model was applied to describe the effect of dose on bioavailability. The oral clearance was estimated to be 11.1 L/h. The volume of distribution was characterized as 81.0 L. The absorption rate constant was estimated at 0.860 h^-1, and the lag time was predicted at 0.311 h. Oral bioavailability was estimated to be 68.8% at dose of 300 mg, 62.7% at dose of 400 mg, and 47.1% at dose of 800 mg. The creatinine clearance significantly influenced on the oral clearance (P < 0.005) and ABCB1 2677G > T/A genotypes significantly influenced on the absorption rate constant (P < 0.05) of gabapentin. However, ABCB1 1236C > T and 3435C > T genotypes showed no significant effect on gabapentin PK parameters. The results of the present study indicate that the oral bioavailability of gabapentin is decreased when its dosage is increased. In addition, ABCB1 2677G > T/A polymorphism can explain the substantial inter-individual variability in the absorption of gabapentin.

Factors in Variability of Serial Gabapentin Concentrations in Elderly Patients with Epilepsy

OBJECTIVES

To characterize and quantify the variability of serial gabapentin concentrations in elderly patients with epilepsy.

METHODS

This study included 83 patients (age ≥ 60 yrs) from an 18-center randomized double-blind double-dummy parallel study from the Veterans Affairs Cooperative 428 Study. All patients were taking 1500 mg/day gabapentin. Within-person coefficient of variation (CV) in gabapentin concentrations, measured weekly to bimonthly for up to 52 weeks, then quarterly, was computed. Impact of patient characteristics on gabapentin concentrations (linear mixed model) and CV (linear regression) were estimated.

RESULTS

A total of 482 gabapentin concentration measurements were available for analysis. Gabapentin concentrations and intrapatient CVs ranged from 0.5 to 22.6 μg/ml (mean 7.9 μg/ml, standard deviation [SD] 4.1 μg/ml) and 2% to 79% (mean 27.9%, SD 15.3%), respectively, across all visits. Intrapatient CV was higher by 7.3% for those with a body mass index of ≥ 30 kg/m² (coefficient = 7.3, p=0.04). CVs were on average 0.5% higher for each 1-unit higher CV in creatinine clearance (coefficient = 0.5, p=0.03) and 1.2% higher for each 1-hour longer mean time after dose (coefficient = 1.2, p=0.04).

CONCLUSIONS

Substantial intrapatient variability in serial gabapentin concentration was noted in elderly patients with epilepsy. Creatinine clearance, time of sampling relative to dose, and obesity were found to be positively associated with variability.

[Perioperative gabapentin and pregabalin in cardiac surgery: a systematic review and meta-analysis]

OBJECTIVES

Sternotomy for cardiac surgeries causes significant postoperative pain and when not properly managed may cause significant morbidity. As neuropathic pain is a significant component here, gabapentin and pregabalin may be effective in these patients and may reduce postoperative opioid consumption. The purpose of this systematic review was to find out efficacy of gabapentin and pregabalin in acute postoperative pain after cardiac surgery.

METHODS

Published prospective human randomized clinical trials, which compared preoperative and/or postoperative gabapentin/pregabalin with placebo or no treatment for postoperative pain management after cardiac surgery has been included in this review.

RESULTS

Four RCTs each for gabapentin and pregabalin have been included in this systematic review. Three gabapentin and two pregabalin studies reported decrease in opioid consumption in cardiac surgical patients while one gabapentin and two pregabalin studies did not. Three RCTs each for gabapentin and pregabalin reported lower pain scores both during activity and rest. The drugs are not associated with any significant complications.

CONCLUSION

Despite lower pain scores in the postoperative period, there is insufficient evidence to recommend routine use of gabapentin and pregabalin to reduce opioid consumption in the cardiac surgical patients.

Perspectives on variability in pharmacokinetics of an oral contraceptive product

The early literature and reviews have described the pharmacokinetics (PK) of oral contraceptive (OC) compounds such as ethinyl estradiol (EE) and levonorgestrel (LNG) in women as subject to large intersubject variability. This was partly due to the use of diverse radioimmunoassays, limited sampling periods and an incomplete understanding of single- vs. multiple-dose kinetics and the role of EE in causing both inhibition of hepatic metabolism along with induction of sex hormone binding globulin. Over the past two decades, LNG and EE have been used as target drugs for the assessment of possible drug interactions upon introduction of many new therapeutic agents. This has resulted in at least 17 publications that describe the PK of LNG and EE in women using various 150 mcg/30 mcg products under fairly standard multiple-dose conditions. A review of these studies indicates only moderate variability in the C_max and area under the curve both within and across these studies. There is impressive similarity in these drug exposure indices found in studies carried out with several products by investigators at numerous sites and countries.

Changes in utilisation of antiepileptic drugs in epilepsy and non-epilepsy disorders-a pharmacoepidemiological study and clinical implications

PURPOSE

The purpose of this study was to investigate changes in utilisation of antiepileptic drugs (AEDs) in epilepsy and non-epilepsy disorders in Norway and furthermore to study the retention rates of the most commonly used AEDs in these indications in long-term use.

METHODS

The data consisted of all prescriptions of AEDs from Norwegian pharmacies in the Norwegian Prescription Database (NorPD) (2004-2012). Variables included anonymous data regarding age, gender, diagnosis specific reimbursement codes and utilisation of AEDs.

RESULTS

In recent years (2008-2012), the utilisation of AEDs in non-epilepsy disorders accounted for 45-53 % of the total use. In epilepsy, the most commonly used AED was lamotrigine, followed by levetiracetam, carbamazepine and valproate. Lamotrigine was also the predominant AED used in psychiatry, while pregabalin and gabapentin were mostly used in neuropathic pain. In migraine, topiramate predominated but accounted for <1 % of the total utilisation of AEDs. The majority of prescriptions were by general practitioners and only 20 % by specialists. Regardless of indication, newer AEDs had higher retention rates (34-48 %) and were used for a longer period before discontinuation.

CONCLUSIONS

The use of AEDs in non-epilepsy disorders is increasing and accounted for 53 % in 2012. Newer AEDs were predominantly used and demonstrated higher retention rates than older AEDs in all indications. This nationwide study demonstrates an increased exposure to AEDs in new patient groups, and details in prescription patterns and clinical and safety considerations should be closely monitored. This contributes to long-term post-marketing data of AED and accordingly improved pharmacovigilance.

Alpha2delta ligands, gabapentin, pregabalin and mirogabalin: a review of their clinical pharmacology and therapeutic use

INTRODUCTION

The first two alpha₂delta ligands - gabapentin (GBP) and pregabalin (PGB) - were initially synthesized as antiepileptics; however, they were later also found to be useful for the treatment of additional conditions. Areas covered: Relevant publications describing potential underlying mechanisms, clinical pharmacokinetics/pharmacokinetics, and clinical efficacy and safety of these drugs in various disease conditions were searched in PubMed and Scopus and included in this review. Expert commentary: GBP and PGB are effective for the treatment neuropathic pain, fibromyalgia and epilepsy; in addition, they may be useful for the reduction of postoperative pain. PGB is also effective for the treatment of generalized anxiety disorder and GBP for the treatment of restless legs syndrome. GBP may be considered a treatment option for pain associated with Guillain-Barré Syndrome and phantom limb and for the management of uremic pruritus. Mirogabalin (MGB), recently developed, is being investigated for the treatment of peripheral neuropathic pain and fibromyalgia, showing promising results in patients with diabetic peripheral neuropathy. Their most frequent adverse reactions are of neuropsychiatric nature and include fatigue, dizziness, sedation, somnolence, and ataxia; peripheral edema and weight gain are also frequently described. Pharmacokinetic interactions are scarce; however, pharmacodynamic interactions have been described in association with drugs with CNS-depressant effects.

Pharmacokinetic Properties of New Antiepileptic Drugs

Eight new antiepileptic drugs (AEDs) have been approved for use within the United States within the past decade. They are felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, and zonisamide. These afford clinicians with more options to increase efficacy and tolerability in the treatment of patients with epilepsy. Pharmacokinetic properties and drug interactions with other AEDs and other medications taken for comorbidities are individually discussed for each of these new agents. Drug concentrations are not routinely monitored for these newer agents, and there have been few studies designed to investigate their concentration-effect relationships. For most of these medications, the concentrations observed in responders and nonresponders overlap considerably and levels associated with efficacy are often associated with adverse events, complicating the definition of target ranges. Also, epilepsy manifests itself sporadically causing difficulty in clinically monitoring efficacy of medications. Therapeutic drug monitoring provides for the individualization of treatment for these agents, which is important because they demonstrate significant variability in inter- and intraindividual pharmaco-kinetic properties. Therapeutic drug monitoring also allows for identification of noncompliance, drug interactions, and toxicity. Current knowledge of the relationships between efficacy, toxicity, and drug concentrations is discussed.

A case of gait disturbance caused by low-dose gabapentin

Gabapentin, an anticonvulsant agent, is now often used for the treatment of neuropathic pain all over the world. It is unclear whether the combined use of gabapentin, sodium valproate, and flunitrazepam results in enhancement of the side effect, a gait disturbance. A 60-year-old man was taking oral sodium valproate for symptomatic epilepsy after a brain contusion and flunitrazepam to relieve insomnia. Oral gabapentin therapy was started for suspected neuropathic pain. Although the initial dose of oral gabapentin (200 mg) relieved the pain, the lower extremities became weak, resulting in a gait disturbance. The therapy was restarted with a halved dose, and this resolved the gait disturbance and relieved the pain.

Impact of Data Imputation Methodology on Pain Assessment over 24 Hours in a Randomized, Placebo-Controlled Study of Gabapentin Enacarbil in Patients with Neuropathic Pain Associated with Postherpetic Neuralgia

OBJECTIVE

To assess the impact of gabapentin enacarbil on primary and secondary pain endpoints using three data imputation methodologies in a randomized phase II study of adult patients with postherpetic neuralgia.

METHODS

The primary endpoint was change from baseline to end of maintenance treatment in mean 24-hour average pain intensity score. Secondary endpoints (daytime/nighttime average pain intensity score, daytime/nighttime current pain intensity score, and daytime/nighttime worst pain intensity score) were based on daily electronic diary assessments. Comparisons of each gabapentin enacarbil dose with placebo were performed using three different statistical methodologies: last observation carried forward, baseline observation carried forward, and mixed-effect model for repeated measures.

RESULTS

Of the 376 randomized patients, 371 were in the intent-to-treat population (gabapentin enacarbil 1,200 mg, 107; 2,400 mg, 82; 3,600 mg, 87; placebo, 95). For mean 24-hour average pain intensity score, there were statistically significant improvements from baseline to end of maintenance treatment for all gabapentin enacarbil groups vs placebo using the three analysis methods. Significant improvements were also observed for all secondary endpoints with gabapentin enacarbil 1,200 mg using the three analysis methods. Most secondary endpoints also showed improvements following treatment with gabapentin enacarbil 2,400 mg or 3,600 mg compared with placebo.

CONCLUSIONS

Gabapentin enacarbil (1,200 mg, 2,400 mg, and 3,600 mg) was effective and well tolerated in patients with postherpetic neuralgia compared with placebo, as confirmed by three different and robust statistical methodologies.

Antiepileptic and Antidepressive Polypharmacy in Patients with Multiple Sclerosis

Objective. Patients with multiple sclerosis (MS) are often suffering from neuropathic pain. Antiepileptic drugs (AEDs) and tricyclic antidepressants (TCAs) are commonly used and are susceptible to be involved in drug interactions. The aim of this retrospective study was to investigate the prevalence of use of antiepileptic and antidepressive drugs in MS patients and to discuss the theoretical potential for interactions. Methods. Review of the medical records from all patients treated at a dedicated MS rehabilitation centre in Norway between 2009 and 2012. Results. In total 1090 patients attended a rehabilitation stay during the study period. Of these, 342 (31%; 249 females) with mean age of 53 (±10) years and EDSS 4.8 (±1.7) used at least one AED (gabapentin 12.7%, pregabalin 7.7%, clonazepam 7.8%, and carbamazepine 2.6%) or amitriptyline (9.7%). Polypharmacy was widespread (mean 5.4 drugs) with 60% using additional CNS-active drugs with a propensity to be involved in interactions. Age, gender, and EDSS scores did not differ significantly between those using and not using AED/amitriptyline. Conclusion. One-third of MS patients attending a rehabilitation stay receive AED/amitriptyline treatment. The high prevalence of polypharmacy and use of CNS-active drugs calls for awareness of especially pharmacodynamic interactions and possible excessive adverse effects.

Pharmacokinetic effects of simultaneous administration of single-dose gabapentin 500 mg and zolpidem tartrate 10 mg in healthy volunteers: a randomized, open-label, crossover trial

Objective

Gabapentin is being investigated as a potential treatment for occasional disturbed sleep. This study assessed the pharmacokinetics and tolerability of gabapentin 500 mg and the commonly prescribed sedative/hypnotic zolpidem tartrate 10 mg, administered separately and in combination.

Methods

Forty healthy participants (19 male, 21 female) were randomized into this three-period crossover study [mean (range) age 34.1 (18–45) years, weight 68.3 (51.4–92.7) kg; 60 % white]. Participants were dosed with gabapentin alone (n = 39), zolpidem tartrate alone (n = 38), and the combination (gabapentin + zolpidem) (n = 38) over three treatment periods, which were separated by ≥7 days. Blood samples were collected pre-dose and 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 18, 24 and 36 h post-dose. Plasma concentrations of each drug were assayed using validated methods. Pharmacokinetic parameters were estimated from plasma concentration–time data using standard non-compartmental methods.

Results

For gabapentin + zolpidem combination versus gabapentin alone, mean pharmacokinetic parameters were peak plasma concentration (C_max) 4.61 versus 4.72 µg/mL, time to C_max (t_max) 4.63 versus 3.64 h and the area under plasma concentration–time curve extrapolated to infinity (AUC_0–∞) 53.4 versus 51.0 µg h/mL. For the combination versus zolpidem alone, mean pharmacokinetic parameters were C_max 154 versus 138 ng/mL, t_max 1.45 versus 1.84 h and AUC_0–∞ 912 versus 854 ng h/mL. The 90 % confidence intervals for C_max (rate of absorption) and AUC_0–∞ (extent of absorption) comparing the combination versus single drug administration fell within the 80–125 % range accepted for bioequivalence. All treatments were well tolerated.

Conclusion

The pharmacokinetics of gabapentin 500 mg and zolpidem tartrate 10 mg are unaffected when both drugs are taken simultaneously, compared with each drug taken alone.

Analgesic effects of gabapentin after scoliosis surgery in children: a randomized controlled trial

BACKGROUND

Postoperative pain remains an important challenge after scoliosis surgery in children. Opioids are the mainstay of treatment, and adult studies demonstrate gabapentin as a useful adjunct to opioids in the management of postoperative pain.

METHOD

Adolescent patients undergoing idiopathic scoliosis surgery were randomized to receive a single preoperative dose of gabapentin 600 mg or placebo. The primary outcome measure was total morphine consumption in mg·kg(-1) between 0 and 24 h postoperatively. Secondary outcome measures included time to first rescue analgesia, pain intensity scores at rest and with movement, incidence of nausea, vomiting, pruritus, sedation, dizziness, presence of persisting pain symptoms, and patient satisfaction. Cumulative opioid consumption was calculated at each time point: 1, 4, 8, 12, 24, 48, and 72 h.

RESULTS

The gabapentin group used 0.087 ± 0.06 mg·kg(-1) of morphine at 1 h, 0.24 ± 0.12 mg·kg(-1) at 4 h, 0.44 ± 0.17 mg·kg(-1) at 8 h, and 1.29 ± 0.44 mg·kg(-1) at 24 h. The placebo group used 0.121 ± 0.06 mg·kg(-1) of morphine at 1 h, 0.35 ± 0.16 mg·kg(-1) at 4 h, 0.56 ± 0.27 mg·kg(-1) at 8 h, and 1.46 ± 0.68 mg·kg(-1) at 24 h. There was no statistically significant reduction in opioid consumption in the patients receiving gabapentin. There were no significant differences in secondary outcomes.

CONCLUSION

A single preoperative dose of gabapentin did not show a significant difference in opioid consumption or pain scores in adolescents undergoing idiopathic scoliosis surgery. This study is the first pediatric randomized controlled trial to assess the effectiveness of a single dose of gabapentin on morphine consumption and analgesia following major surgery.

Single dose pharmacokinetic equivalence study of two gabapentin preparations in healthy subjects

BACKGROUND

The current study was conducted to find out whether two oral preparations of 300 mg gabapentin (the test and reference capsules) were bioequivalent.

SUBJECTS AND METHODS

This was a randomized, single-blind, crossover study under fasting condition, with a 7-day washout period, which included 37 healthy adult male and female subjects. After an overnight fast, subjects were given, orally, one capsule of the test drug or of the reference drug. Blood samples were drawn immediately before taking the drug, then at 20 and 40 minutes, and 1, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 15, and 24 hours after dosing, to evaluate pharmacokinetic parameters of the single dose administration, ie, the area under the plasma concentration-time curve (AUC) from time zero to 24 hours (AUCt), AUC from time zero to infinity (AUC(inf)), the peak plasma concentration of the drug (Cmax), time needed to achieve Cmax (tmax), and the elimination half-life (t1/2). The plasma concentrations of gabapentin were determined using validated high-performance liquid chromatography with ultraviolet detection.

RESULTS

The geometric mean ratios (90% confidence interval) of the test drug/reference drug for gabapentin were 103.15% (90.38%-117.72%) for AUCt, 103.53% (90.78%-118.07%) for AUC(inf), and 108.06% (96.32%-121.24%) for Cmax. The differences in tmax and t1/2 values between the test and reference drug products for gabapentin were not statistically significant. Light-headedness, nausea, and headache were encountered during the study, but they were all mild and well tolerated. The 90% confidence intervals of the test/reference AUC ratio and Cmax ratio of gabapentin were within the acceptance range for bioequivalence.

CONCLUSION

The two preparations of gabapentin 300 mg capsule were bioequivalent, thus both can be used interchangeably in the clinical setting.

In vivo and in vitro evaluations of intestinal gabapentin absorption: effect of dose and inhibitors on carrier-mediated transport

PURPOSE

Gabapentin exhibits saturable absorption kinetics, however, it remains unclear which transporters that are involved in the intestinal transport of gabapentin. Thus, the aim of the current study was to explore the mechanistic influence of transporters on the intestinal absorption of gabapentin by both in vivo and in vitro investigations

METHODS

Pharmacokinetic parameters were determined following a range of intravenous (5-100 mg/kg) and oral doses (10-200 mg/kg) in rats. Transepithelial transport (50 μM-50 mM) and apical uptake of gabapentin (0.01-50 mM) were investigated in Caco-2 cells. The effect of co-application of the LAT-inhibitor, BCH, and the b(0,+)-substrate, L-lysine, on intestinal transport of gabapentin was evaluated in vivo and in vitro.

RESULTS

Gabapentin showed dose-dependent oral absorption kinetics and dose-independent disposition kinetics. Co-application of BCH inhibited intestinal absorption in vivo and apical uptake in vitro, whereas no effect was observed following co-application of L-lysine.

CONCLUSIONS

The present study shows for the first time that BCH was capable of inhibiting intestinal absorption of gabapentin in vivo. Furthermore, in Caco-2 cell experiments BCH inhibited apical uptake of gabapentin. These findings may imply that a BCH-sensitive transport-system was involved in the apical and possibly the basolateral transport of gabapentin across the intestinal wall.

Albumin nanoparticles for the delivery of gabapentin: preparation, characterization and pharmacodynamic studies

The study was aimed to prepare and evaluate gabapentin loaded albumin nanoparticles and to find out their effectiveness in treating epilepsy. Albumin nanoparticles of gabapentin were prepared by pH-coacervation method. The drug was administered into animals as free drug, gabapentin bound with nanoparticles, and gabapentin bound with nanoparticles coated with polysorbate 80. The polysorbate 80 coated nanoparticles increased the gabapentin concentration in the brain about 3 fold in comparison with the free drug. Moreover, the polysorbate 80 coated nanoparticles significantly reduced the duration of all phases of convulsion in both maximal electroshock induced and pentylenetetrazole induced convulsion models in comparison with free drug and drug bound with nanoparticle formulations, which indicates the ability of polysorbate 80 coated nanoparticles to enhance the gabapentin concentration in the brain.

Gabapentin's anti-nausea and anti-emetic effects: a review

Gabapentin's main clinical use is in the treatment of neuropathic pain where its binding to neuronal alpha-2/delta subunits of voltage-gated calcium channels (VGCCs) is critical to its mechanism of action. Over the past 10 years, there have been several reports of gabapentin also having anti-nausea and anti-emetic effects in conditions including postoperative nausea and vomiting (PONV), chemotherapy-induced nausea and vomiting (CINV), and hyperemesis gravidarum (HG). In this report, a MEDLINE electronic search was performed, and relevant citations were reviewed and classified by level of evidence; a grade of recommendation was then assigned for gabapentin's use for each studied indication. Out of 33 clinical trials reviewed, 12 assessed nausea and/or vomiting (N/V) associated with gabapentin therapy as primary outcome measures. These 12 studies provided a Grade A recommendation for gabapentin use in treating PONV, a Grade B recommendation for use in treating CINV, and a Grade C recommendation for use in treating HG. Further research is needed to confirm these initial promising results, which implicate the alpha-2/delta VGCC subunit as a novel therapeutic target in the treatment of several N/V-associated clinical conditions.

New approaches to the pharmacotherapy of neuropathic pain

Pain is one of the most debilitating symptoms that presents with neuropathy. Neuropathic pain syndrome is a challenge to treat and, even with appropriate evidence-based treatment, only a 40% reduction of symptoms can be achieved in approximately half of patients. Furthermore, efficient doses are often difficult to obtain because of adverse effects. These observations underline that the treatment of neuropathic pain is still an unmet medical need. New approaches to the pharmacotherapy of neuropathy embrace different lines of work, including a fundamental mechanism-based approach, a clinical mechanism-based approach and an evidence-based approach. Moreover, interindividual variability in drug response, and genetic polymorphism in particular, is an emerging aspect to consider. Together with reviewing recent evidence-based guidelines as well as briefly discussing genetic polymorphisms that may influence the individual responses to treatments, this article will focus on what a mechanism-based approach is bringing to the clinical setting, on the perspective in fundamental research and on the difficulty of bridging the gap between fundamental notions and positive clinical outcomes.

Gabapentin enacarbil for the treatment of moderate to severe primary restless legs syndrome (Willis-Ekbom disease): 600 or 1,200 mg dose?

Gabapentin enacarbil is a prodrug of the anticonvulsant gabapentin. The efficacy and safety of gabapentin enacarbil for the treatment of moderate to severe primary restless legs syndrome (RLS) has been evaluated in several clinical trials in the United States and Japan. Although most clinical trials assessed gabapentin enacarbil at doses greater than 600 mg/day and demonstrated the overall safety and efficacy (defined as improvements in the coprimary endpoints of the international RLS rating scale [IRLS] total score and Clinical Global Impression-Improvement response), the US Food and Drug Administration approved the 600 mg once-daily dosage because doses higher than 600 mg/day were considered to provide no additional benefits and were associated with higher rates of adverse events, such as somnolence and dizziness. Nonetheless, the results of clinical trials and post hoc meta-analyses have indicated that the 1,200 mg once-daily dosage was the most validated gabapentin enacarbil treatment for not only subjective RLS symptoms but also severe sleep disturbance associated with RLS. A Japanese dose-finding study showed that 900 mg/day, the intermediate dose between 600 and 1,200 mg, failed to show a significant improvement in IRLS total score, probably because many of the patients who discontinued treatment did so early, suggesting that a half-landing dose may cause more adverse effects than favorable ones in some RLS patients early in the treatment. Gabapentin enacarbil may have two distinct therapeutic doses for the treatment of RLS: 600 mg/day or lower doses for the treatment of subjective RLS symptoms and 1,200 mg/day or higher doses for the treatment of both subjective RLS symptoms and associated problems such as severe sleep disturbances.

Integration of biological clocks and rhythms

Animals, plants, and microorganisms exhibit numerous biological rhythms that are generated by numerous biological clocks. This article summarizes experimental data pertinent to the often-ignored issue of integration of multiple rhythms. Five contexts of integration are discussed: (i) integration of circadian rhythms of multiple processes within an individual organism, (ii) integration of biological rhythms operating in different time scales (such as tidal, daily, and seasonal), (iii) integration of rhythms across multiple species, (iv) integration of rhythms of different members of a species, and (v) integration of rhythmicity and physiological homeostasis. Understanding of these multiple rhythmic interactions is an important first step in the eventual thorough understanding of how organisms arrange their vital functions temporally within and without their bodies.

Intrathecal gabapentin to treat chronic intractable noncancer pain

BACKGROUND

Oral gabapentin is approved as an anticonvulsant medication and to treat postherpetic neuralgia. Its nonopioid properties and presumed spinal site of analgesic action made the study on intrathecal gabapentin attractive to establish the minimum effective dose for a later, pivotal trial.

METHODS

The authors examined the safety and efficacy of intrathecal gabapentin in a randomized, blinded, placebo-controlled, multicenter trial in a heterogeneous cohort of candidates with chronic pain for intrathecal drug therapy.

RESULTS

Patients (N = 170) were randomized to receive continuous intrathecal gabapentin (0 [placebo], 1, 6, or 30 mg/day) during 22 days of blinded treatment after implantation of a permanent drug delivery system. The highest dose, 30 mg/day, was selected to maintain a safety margin below the 100-mg/day dose that was explored in a phase 1 study. The authors found no statistically significant difference in the primary outcome measure, which was the numerical pain rating scale and response rate after 3 weeks, for any dose versus placebo. Physical functioning, quality of life, and emotional functioning also revealed no differences. Small, nonsignificant changes occurred in opioid medication use. The most frequent device-related adverse events were transient postimplant (lumbar puncture) headache, pain, and nausea. The most frequent gabapentin-related adverse events were nausea, somnolence, headache, dizziness, fatigue, and peripheral edema.

CONCLUSION

Twenty-two days of intrathecal gabapentin did not demonstrate statistically significant or clinically meaningful analgesic effects. The study sponsor has no current plans for further studies. Drug-related adverse events were similar to those for oral gabapentin. Most device-related adverse events resulted from the implant surgery or anesthesia.

Therapeutic drug monitoring of antiepileptic drugs by use of saliva

Blood (serum/plasma) antiepileptic drug (AED) therapeutic drug monitoring (TDM) has proven to be an invaluable surrogate marker for individualizing and optimizing the drug management of patients with epilepsy. Since 1989, there has been an exponential increase in AEDs with 23 currently licensed for clinical use, and recently, there has been renewed and extensive interest in the use of saliva as an alternative matrix for AED TDM. The advantages of saliva include the fact that for many AEDs it reflects the free (pharmacologically active) concentration in serum; it is readily sampled, can be sampled repetitively, and sampling is noninvasive; does not require the expertise of a phlebotomist; and is preferred by many patients, particularly children and the elderly. For each AED, this review summarizes the key pharmacokinetic characteristics relevant to the practice of TDM, discusses the use of other biological matrices with particular emphasis on saliva and the evidence that saliva concentration reflects those in serum. Also discussed are the indications for salivary AED TDM, the key factors to consider when saliva sampling is to be undertaken, and finally, a practical protocol is described so as to enable AED TDM to be applied optimally and effectively in the clinical setting. Overall, there is compelling evidence that salivary TDM can be usefully applied so as to optimize the treatment of epilepsy with carbamazepine, clobazam, ethosuximide, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, phenobarbital, phenytoin, primidone, topiramate, and zonisamide. Salivary TDM of valproic acid is probably not helpful, whereas for clonazepam, eslicarbazepine acetate, felbamate, pregabalin, retigabine, rufinamide, stiripentol, tiagabine, and vigabatrin, the data are sparse or nonexistent.

Epilepsy, cognition, and neuropsychiatry (Epilepsy, Brain, and Mind, part 2)

Epilepsy is, of course, not one disease but rather a huge number of disorders that can present with seizures. In common, they all reflect brain dysfunction. Moreover, they can affect the mind and, of course, behavior. While animals too may suffer from epilepsy, as far as we know, the electrical discharges are less likely to affect the mind and behavior, which is not surprising. While the epileptic seizures themselves are episodic, the mental and behavioral changes continue, in many cases, interictally. The episodic mental and behavioral manifestations are more dramatic, while the interictal ones are easier to study with anatomical and functional studies. The following extended summaries complement those presented in Part 1.

Administration of four different doses of gabapentin reduces awakening from breakthrough pain and adverse effects in outpatients with neuropathic pain during the initial titration

Background

Gabapentin is a safe and well-tolerated anticonvulsant with a wide therapeutic index, and it is used for neuropathic pain. The aim of this study was to compare previous dosing methods with the administration of four different doses of gabapentin while maintaining the same maximum daily dose for the safe administration of high doses of the medication.

Methods

The subjects were outpatients with various neuropathic pain syndromes, with at least two of the following symptoms: allodynia, burning pain, shooting pain, or hyperalgesia. The TID group received equal doses of gabapentin 3 times per day, while the QID group received 4 different doses of gabapentin per day. The pain score, frequency of breakthrough pain (BTP), severity and the duration of pain, sleep disturbance due to nocturnal pain, and adverse effects were recorded each day.

Results

The average daily pain score and sleep disturbance were significantly reduced in the QID group between days 3 and 10 of the experiment. The adverse effects of the medication were also reduced in the QID group. However, the frequency of BTP and severity and duration of pain were not significantly different between two groups.

Conclusions

Administration of 4 different doses of gabapentin during the initial titration in outpatients with neuropathic pain resulted in a significant reduction in awakening from breakthrough pain and a reduction in the adverse effects of the medication.

Gabapentin to pregabalin therapy transition: a pharmacokinetic simulation

The objective of this modeling study was to assess different dosage regimens that might be used to guide clinicians in transitioning patients from gabapentin to pregabalin therapy when such a transition is clinically warranted. Two different gabapentin to pregabalin transition designs were simulated based on their respective population pharmacokinetic profiles. The first design involved immediate discontinuation of gabapentin therapy with initiation of pregabalin therapy at the next scheduled dose period. The second design featured a gradual transition involving coadministration of 50% of the gabapentin dosage and 50% of the desired pregabalin dosage for 4 days, followed by discontinuation of gabapentin and fully targeted dosages of pregabalin. Both transition designs were studied at 3 dosage levels: gabapentin 900 mg/d to pregabalin 150 mg/d, gabapentin 1800 mg/d to pregabalin 300 mg/d, and gabapentin 3600 mg/d to pregabalin 600 mg/d. Overall drug exposure achieved during the 2 transition designs was the sum of the gabapentin and pregabalin concentrations, expressed as pregabalin-equivalent concentrations. The pharmacokinetic simulations show that during the transition period in both designs, predicted pregabalin-equivalent concentrations did not depart from those calculated during periods of steady-state gabapentin or pregabalin monotherapy. Transition from gabapentin to pregabalin was seamless and rapid, with predicted pregabalin-equivalent concentrations highly comparable with plasma pregabalin concentrations within 1 day of pregabalin initiation in the immediate discontinuation model and within 1 day of gabapentin cessation in the gradual discontinuation model. These data suggest that transitioning patients from gabapentin to pregabalin could theoretically be achieved by either of the 2 approaches assessed.