Oral absorption kinetics of levetiracetam: the effect of mixing with food or enteral nutrition formulas

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.

Bifari I, Ahmed Alharbi Y. Unraveling medication errors in enteral tube administration: A cross-sectional study in geriatric patients receiving home health care

Background

Medication administration through enteral feeding tubes requires careful consideration, as several medications are unsuitable for such administration due to interactions with feeding formulas or adverse effects when crushed. These errors can lead to feeding tube obstruction, reduced drug efficacy, or drug toxicity.

Objective

This study aimed to assess medication errors in geriatric patients using enteral feeding tubes who were enrolled in a home health care program.

Method

This was a cross-sectional observational study conducted at the Ministry of Health Government Hospital in Makkah City, Saudi Arabia. Medication errors related to chronic oral drugs in geriatric patients using enteral feeding tubes were evaluated, including inappropriate medications for enteral tube administration, inappropriate preparation, drug-nutrient interaction, and availability of liquid formulation, following established guidelines.

Results

Of the total 233 medications prescribed to 46 patients receiving enteral tube feeding at home, 49.3% exhibited at least one form of medication error, totaling 135 errors. Medication errors were highly prevalent among the patients (93.4%), with the leading cause being the administration of medications unsuitable for enteral feeding tubes (33.3%), predominantly due to the use of controlled release or enteric-coated formulations.

Conclusion

This study underscores the high prevalence of medication errors in older patients receiving enteral feeding at home. To ensure patient safety and optimal outcomes, healthcare professionals should utilize available resources and seek expert advice when selecting medications and dosage forms for tube-fed patients. Pharmacists play a critical role in promoting safe drug use and can greatly contribute by educating patient caregivers on proper medication preparation and administration techniques, thus preventing harm to patients.

Vehicles for Drug Administration to Children: Results and Learnings from an In-Depth Screening of FDA-Recommended Liquids and Soft Foods for Product Quality Assessment

Purpose

Mixing with liquids or soft foods is a common procedure to improve acceptability of oral medicines in children but may affect drug stability and the in vivo performance of the administered drug product. The aim of the present study was to obtain an overview of the variability of critical attributes of commonly used vehicles and to identify which vehicle characteristics need to be considered when developing in vitro methods for evaluating product quality.

Methods

One product of each vehicle listed in the FDA draft guidance “Use of Liquids and/or Soft Foods as Vehicles for Drug Administration” was analyzed with regard to composition, calorific content and physicochemical properties.

Results

The studied vehicles show wide variability, both in composition and physicochemical properties. No correlation was observed between vehicle composition and physicochemical properties. Comparison of results of the present study with previously published data also provided variability in physicochemical properties within individual vehicle types.

Conclusions

To identify acceptable (qualified) vehicles for global drug product labeling, it is important that the vehicles selected for in vitro compatibility screening reflect the variability in composition and essential physicochemical properties of the vehicles recommended on the product label, rather than relying on results obtained with a single vehicle of each type. Future activities will focus on the development of standardized dosing vehicles that can represent key vehicle characteristics in all their variability to ensure reliable risk assessment.

Patient with bipolar I disorder who presented with low blood lithium levels after receiving crushed tablets via a nasogastric tube: A case report

In clinical psychiatric cases, the placement of a nasogastric tube is occasionally considered. If a patient who presents with mania or other psychiatric conditions refuses to take drugs, they are administered via the nasogastric tube. The tablet is crushed, suspended, passed via the nasogastric line, and reaches the stomach directly. However, the effects of these processes on blood drug concentrations remain unclear. Herein, we report a patient with bipolar I disorder who presented with low blood lithium carbonate (Li) concentrations after receiving the drug via the nasogastric tube.

CASE

A 26-year-old woman developed manic symptoms with grandeur delusion. She was admitted to a psychiatric hospital three times after diagnosis. Her manic symptoms with delusion improved with Li and aripiprazole (ARP). Her condition stabilized with Li 800 mg/day and ARP 9 mg/day. After the Li dose was reduced to 600 mg/day, she maintained remission, with the blood level range of Li being 0.31 ∼ 0.42 mEq/L. After 1 year, she was admitted to our hospital due to a jaw deformity. During the perioperative period, treatment with oral Li was discontinued by the surgeons, and her manic symptoms recurred. During therapy with olanzapine 20 mg and Li 800 mg, her blood Li concentration was 0.67 mEq/L. The symptoms remained. Hence, the Li dose increased to 1,000 mg/day. However, she refused to take the medication. Thus, a nasogastric tube was used to administer medicines. Thereafter, the blood Li concentration decreased to 0.43 mEq/L, which was lesser than 800 mg/day. Each blood sample was collected approximately 18 h after the administration. Her symptoms remained. Thereafter, she agreed to take the medication, and the Li concentration reached 0.78 mEq/L. Then, the symptoms partly improved.

CONCLUSION

After the administration of Li via the nasogastric tube, the Li concentration decreased, which was lower than expected. This phenomenon could be attributed to the fact that the medication was crushed, suspended, and administered via the nasogastric tube. Therefore, pulverizing and administering Li tablets via the nasogastric tube can be applied for the management of mania, however, caution should be observed because of the risk of fluctuations in blood Li levels, as in this case.

The Pharmacokinetics of Crushed Levetiracetam Tablets Administered to Neonates

BACKGROUND

Intravenous phenobarbital remains the first-line therapy in the management of neonatal seizures. Shortages of intravenous phenobarbital in South Africa necessitated the addition of oral levetiracetam as part of management of neonatal seizures.

OBJECTIVE

We evaluated the pharmacokinetics of crushed immediate-release levetiracetam tablets administered to neonates to terminate seizures.

METHODS

A prospective, observational study of neonates admitted with seizures to Tygerberg Hospital. Participants received crushed levetiracetam (diluted in saline) given orally or via naso-/orogastric tube. At steady-state, pharmacokinetic sampling was performed at pre-dose, 1.5, 2.5 and 4 h post-dose. Maximum concentration (Cmax), time to Cmax (Tmax), trough concentrations (Ctrough) and area under the concentration-time curve (AUC0-12) were calculated using non-compartmental analysis. Seizure termination and safety profiles were documented.

RESULTS

Nineteen participants were grouped into three dosing ranges: (i) 5-15 mg/kg/12-hourly, (ii) 15-25 mg/kg/12-hourly and (iii) 25-35 mg/kg/12-hourly. Range 1 demonstrated AUC0-12 167.0 ± 45.6 h*μg/mL, Cmax 19.19 ± 4.12 μg/mL and Ctrough 9.99 ± 3.86 µg/mL. Range 2, AUC0-12 316.5 ± 108.4 h*μg/mL, Cmax 35.12 ± 10.54 µg/mL and Ctrough 19.25 ± 8.48 µg/mL. Range 3, AUC0-12 290.9 (range 176.14-405.59) h*μg/mL, Cmax 36.11 (range 27.58-44.64) µg/mL and Ctrough 13.03 (2.98-23.07) µg/mL. Seizures terminated in 17/19 (90%) neonates by day 3 and 19/19 (100%) by day 4 post-levetiracetam initiation.

CONCLUSION

Crushed levetiracetam has comparable pharmacokinetics to historical data. No pharmacokinetic differences were observed between oral vs. naso-/orogastric administration. Crushed levetiracetam tablets can be considered for neonates in low-resource settings where intravenous and syrup access is limited.

LAY SUMMARY

Intravenous preparations of antiepileptic medications are used in the management of neonatal seizures. Various established standard of care intravenous antiepileptic medicines are unavailable nationally and internationally due to reasons outside our control. This stock shortage included intravenous phenobarbitone which is the first-line treatment for paediatric seizures. Due to phenobarbital shortage, levetiracetam has been identified by the neonatologists at Tygerberg Hospital, Cape Town, South Africa, as a suitable treatment option due to its efficacy and safety profile. However, intravenous levetiracetam and oral syrup is not registered in South Africa. Levetiracetam tablets are being crushed, dissolved and administered to neonates. There are no data available on the absorption of crushed levetiracetam tablets administered to neonates via a nasogastric tube. This study characterized the pharmacokinetic profile of crushed levetiracetam administered to neonates. We selected neonates receiving levetiracetam from the neonatal wards at Tygerberg hospital and drew blood to analyse the levetiracetam concentrations at 4 different time points. We found that the overall exposure of crushed levetiracetam tablets were comparable to the exposures achieved in historical data of the unaltered formulations. We concluded that crushed levetiracetam tablets can be considered for neonates in low resource settings where intravenous and syrup access is limited.

Dosage form modification and oral drug delivery in older people

Many people cannot swallow whole tablets and capsules. The cause ranges from difficulties overriding the natural instinct to chew solids/foodstuff before swallowing, to a complex disorder of swallowing function affecting the ability to manage all food and fluid intake. Older people can experience swallowing difficulties because of co-morbidities, age-related physiological changes, and polypharmacy. To make medicines easier to swallow, many people will modify the medication dosage form e.g. split or crush tablets, and open capsules. Some of the challenges associated with administering medicines to older people, and issues with dosage form modification will be reviewed. Novel dosage forms in development are promising and may help overcome some of the issues. However, until these are more readily available, effective interdisciplinary teams, and improving patient health literacy will help reduce the risk of medication misadventures in older people.

Going down the tubes! Impact on seizure control of antiepileptic medication given via percutaneous feeding tubes

BACKGROUND

Long-term feeding by percutaneous endoscopic gastrostomy tube (PEG) is uncommon but can present significant issues when both nutrition and medication have to be fed down the same tube. This is especially important in people with epilepsy where the dose and bioavailability of antiepileptic drugs are critical to maintain adequate seizure control. This group with long-term PEG tubes is particularly vulnerable and dependent on their carers to provide high standard of care. Indeed, approximately half of the people with long-term feeding tubes suffer from severe intellectual disability which requires careful coordination of all members of the multidisciplinary team. It is all the more important when consideration is given that around 50% of people with severe ID have seizures, mostly treatment resistant.

METHOD

A detailed literature review was conducted with the focus on the numerous factors that can affect medication delivery and absorption with the potential to destabilize seizure control in people with PEG. Issues concerning the site of drug absorption, excipients and dilution, interaction between antiepileptic drugs and the nutritional feed, bioavailability, and problems with the PEG tube are considered.

RESULTS

There is limited research in this area and the studies are often based on small numbers, healthy volunteers or in vitro findings.

CONCLUSION

In the absence of sound research data, seizure control in each patient with a PEG needs to be considered on an individual basis. Establishing a baseline by measuring the serum levels prior to the tube insertion may be helpful, followed by checking the levels after PEG insertion.

Modified-Release Formulations of Second-Generation Antiepileptic Drugs: Pharmacokinetic and Clinical Aspects

Modified-release or extended-release (XR) formulations are used to decrease the frequency of dosing for drugs with rapid elimination, to improve convenience and adherence. Use of a modified-release formulation can decrease the peak to trough fluctuations in serum concentrations and theoretically improve the therapeutic benefit of the drug, by decreasing adverse events associated with the higher peak concentrations. Once-daily formulations of lamotrigine (Lamictal XR(®)), levetiracetam (Keppra XR(®)), oxcarbazepine (Oxtellar XR(®), Apydan(®) extent) and topiramate (Qudexy XR™, Trokendi XR™) are approved for the treatment of focal and/or generalized onset seizures. Other seizure medications have been approved for non-epileptic symptoms. Gabapentin XR (Gralise(®)) is approved for the treatment of post-herpetic neuralgias. Gabapentin enacarbil XR (Horizant(®)) is a prodrug of gabapentin and is indicated for treatment of post-herpetic neuralgia and restless leg syndrome, a novel indication. For all but Qudexy XR™, the tablets/capsules must be swallowed whole, without cutting, crushing or chewing, in order to maintain the XR properties of the formulation. Qudexy XR™ can be swallowed intact or the capsules can be opened and sprinkled onto soft food for those with swallowing difficulties, for example, children and the elderly. The bioavailability of Gralise(®) and Horizant(®) is significantly affected by food, specifically fat content, and should be taken with a meal to maximize absorption. Overall, the primary advantage of the newly released XR formulations is the once-daily dosing to improve convenience and adherence, with very limited data suggesting improved tolerability.

Influence of Food on Paediatric Gastrointestinal Drug Absorption Following Oral Administration: A Review

The objective of this paper was to review existing information regarding food effects on drug absorption within paediatric populations. Mechanisms that underpin food-drug interactions were examined to consider potential differences between adult and paediatric populations, to provide insights into how this may alter the pharmacokinetic profile in a child. Relevant literature was searched to retrieve information on food-drug interaction studies undertaken on: (i) paediatric oral drug formulations; and (ii) within paediatric populations. The applicability of existing methodology to predict food effects in adult populations was evaluated with respect to paediatric populations where clinical data was available. Several differences in physiology, anatomy and the composition of food consumed within a paediatric population are likely to lead to food-drug interactions that cannot be predicted based on adult studies. Existing methods to predict food effects cannot be directly extrapolated to allow predictions within paediatric populations. Development of systematic methods and guidelines is needed to address the general lack of information on examining food-drug interactions within paediatric populations.

Advances in anti-epileptic drug testing

In the past twenty-one years, 17 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are clobazam, ezogabine (retigabine), eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. Therapeutic drug monitoring is often used in the clinical dosing of the newer anti-epileptic drugs. The drugs with the best justifications for drug monitoring are lamotrigine, levetiracetam, oxcarbazepine, stiripentol, and zonisamide. Perampanel, stiripentol and tiagabine are strongly bound to serum proteins and are candidates for monitoring of the free drug fractions. Alternative specimens for therapeutic drug monitoring are saliva and dried blood spots. Therapeutic drug monitoring of the new antiepileptic drugs is discussed here for managing patients with epilepsy.

Drug-nutrient interactions in the intensive care unit: literature review and current recommendations

OBJECTIVE

To describe the interactions between drugs and nutrients and their frequency in the intensive care unit and to assess the professional team's awareness regarding this subject.

METHODS

The keywords "drug interactions" and "nutrition therapy" were searched in the PubMed (specifically MeSH) electronic database. The studies were systematically reviewed for descriptions of the types of interactions between drugs and nutrients, including their frequency and consequences.

RESULTS

Sixty-seven articles were found. Among these, 20 articles were appropriate for the methodology adopted and accomplished the objectives of the study. Of these 20 articles, 14 articles described interactions between drugs and enteral nutrition, three described interactions between drugs and parenteral nutrition, and three described the importance and care required to avoid such interactions.

CONCLUSIONS

The literature about drug and nutrient interactions is limited and suggests the inability of health care teams to recognize the potential for these interactions. Possibly, the elaboration of a protocol to evaluate drug-nutrient interactions will increase the safety and efficacy of therapeutics.

Population pharmacokinetics modeling of levetiracetam in Chinese children with epilepsy

AIM

To establish a population pharmacokinetics (PPK) model of levetiracetam in Chinese children with epilepsy.

METHODS

A total of 418 samples from 361 epileptic children in Peking University First Hospital were analyzed. These patients were divided into two groups: the PPK model group (n=311) and the PPK validation group (n=50). Levetiracetam concentrations were determined by HPLC. The PPK model of levetiracetam was established using NONMEM, according to a one-compartment model with first-order absorption and elimination. To validate the model, the mean prediction error (MPE), mean squared prediction error (MSPE), root mean-squared prediction error (RMSPE), weight residues (WRES), and the 95% confidence intervals (95% CI) were calculated.

RESULTS

A regression equation of the basic model of levetiracetam was obtained, with clearance (CL/F)=0.988 L/h, volume of distribution (V/F)=12.3 L, and K(a)=1.95 h(-1). The final model was as follows: K(a)=1.56 h(-1), V/F=12.1 (L), CL/F=1.04×(WEIG/25)(0.583) (L/h). For the basic model, the MPE, MSPE, RMSPE, WRES, and the 95%CI were 9.834 (-0.587-197.720), 50.919 (0.012-1286.429), 1.680 (0.021-34.184), and 0.0621 (-1.100-1.980). For the final model, the MPE, MSPE, RMSPE, WRES, and the 95% CI were 0.199 (-0.369-0.563), 0.002082 (0.00001-0.01054), 0.0293 (0.001-0.110), and 0.153 (-0.030-1.950).

CONCLUSION

A one-compartment model with first-order absorption adequately described the levetiracetam concentrations. Body weight was identified as a significant covariate for levetiracetam clearance in this study. This model will be valuable to facilitate individualized dosage regimens.

Paediatric nurses' knowledge and practice of mixing medication into foodstuff

Objective

To investigate paediatric nurses' knowledge and understanding of potential drug stability issues caused by mixing medication into foodstuff.

Methods

Self completion of semi-structured questionnaires and face-to-face interviews.

Key findings

Fourteen paediatric mental health and 16 paediatric general nurses (response rate, 71%) were investigated. With the exception of one nurse, all others reported they had modified oral dosage forms, or had mixed medication with food, prior to administration. The most common foodstuffs were fruit yoghurts, diluting juice and (concentrated) fruit juices. More than half of both cohorts felt sufficiently trained in carrying out the procedure, but 27% did not feel sufficiently knowledgeable about drug stability issues. The in-depth interviews highlighted a knowledge deficit as to the nature of clinical problems that could result from performing the procedures and the associated professional liabilities. Some interviewees expressed reservations about the effectiveness of the dose when administered in this way. Co-mixing was perceived as a time-consuming process and preference was expressed for mixing the powdered dosage form into juice or a liquid rather than into solid foods. Several training issues were identified from this study, including more information about drug/food compatibilities and the need for standardised documentation around the procedures which could be implemented at the ward level.

Conclusions

Co-mixing of medication into foodstuff is a common practice. The majority of nurses are unaware of potential drug stability/degradation issues and/or the clinical impact of these practices.

Modern methods for analysis of antiepileptic drugs in the biological fluids for pharmacokinetics, bioequivalence and therapeutic drug monitoring

Epilepsy is a chronic disease occurring in approximately 1.0% of the world's population. About 30% of the epileptic patients treated with availably antiepileptic drugs (AEDs) continue to have seizures and are considered therapy-resistant or refractory patients. The ultimate goal for the use of AEDs is complete cessation of seizures without side effects. Because of a narrow therapeutic index of AEDs, a complete understanding of its clinical pharmacokinetics is essential for understanding of the pharmacodynamics of these drugs. These drug concentrations in biological fluids serve as surrogate markers and can be used to guide or target drug dosing. Because early studies demonstrated clinical and/or electroencephalographic correlations with serum concentrations of several AEDs, It has been almost 50 years since clinicians started using plasma concentrations of AEDs to optimize pharmacotherapy in patients with epilepsy. Therefore, validated analytical method for concentrations of AEDs in biological fluids is a necessity in order to explore pharmacokinetics, bioequivalence and TDM in various clinical situations. There are hundreds of published articles on the analysis of specific AEDs by a wide variety of analytical methods in biological samples have appears over the past decade. This review intends to provide an updated, concise overview on the modern method development for monitoring AEDs for pharmacokinetic studies, bioequivalence and therapeutic drug monitoring.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

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.

Drug monitoring: simultaneous analysis of lamotrigine, oxcarbazepine, 10-hydroxycarbazepine, and zonisamide by HPLC-UV and a rapid GC method using a nitrogen-phosphorus detector for levetiracetam

A high-performance liquid chromatography (HPLC) assay using UV detection is described for the simultaneous measurement of the newer generation anti-epileptic medications lamotrigine, oxcarbazepine (parent drug and active metabolite 10- hydroxycarbazepine), and zonisamide. Detection of all four compounds can be done at 230 nm; however, there is a potential interference with zonisamide in patients on clonazepam therapy. Therefore, the method uses dual wavelength detection: 230 nm for oxcarbazepine and 10-hydroxycarbazepine and 270 nm for lamotrigine and zonisamide. In addition, a simple gas chromatography method using a nitrogen-phosphorus detector is described for the measurement of levetiracetam, another of the recently approved anti-epileptic medications. For both methods, limits of quantitation, linearities, accuracies, and imprecisions cover the therapeutic range for drug monitoring of patients. A wide variety of clinical drugs, including other anti-epileptic drugs, do not interfere with these assays. These procedures would be of special interest to clinical laboratories, particularly due to the limited availability of immunoassays for newer generation anti-epileptic medications and that therapeutic uses of these drugs are expanding beyond epilepsy to other neurologic and psychiatric disorders.

Modulation of AMPA Receptors in Cultured Cortical Neurons Induced by the Antiepileptic Drug Levetiracetam

PURPOSE

The present study explores the hypothesis that the antiepileptic mechanism of action of levetiracetam (LEV) is related to effects on alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor channels in mouse cortical neurons in culture.

METHODS

The neurons were subjected to the whole-cell configuration of the patch-clamp recording technique and were 8-12 days old in culture.

RESULTS

Kainate elicited concentration-dependent (EC(50)= 80 microM) inward currents in all the patched cells. LEV (5-200 microM) itself did not induce inward or outward currents on all patched neurons, whereas it was effective on the kainate- and AMPA-induced current because it significantly decreased the amplitude of these currents. LEV was also able to significantly decrease the total membrane conductance during kainate perfusion, indicating that its effect was not dependent on the cellular voltage membrane potential. Further evidence that LEV modulated the ionotropic non-NMDA receptors came from the analysis of miniature excitatory postsynaptic currents (mEPSCs). In fact, LEV significantly decreased both the amplitude and the frequency of mEPSCs, as shown by the relative cumulative distributions.

CONCLUSIONS

These results reveal that AMPA receptors are modulated by LEV because a significant decrease in the kainate- and AMPA-induced currents and a decrease in amplitude and in frequency of mEPSCs have been observed in cortical neurons in culture. The described effect of LEV on AMPA receptors in cortical neurons is probably due to the etheromeric composition of the receptors and may be considered as a possible new antiepileptic mechanism of action.