Comparison of the pharmacokinetics of lamotrigine in patients with chronic renal failure and healthy volunteers

Incorporating Breastfeeding-Related Variability with Physiologically Based Pharmacokinetic Modeling to Predict Infant Exposure to Maternal Medication Through Breast Milk: a Workflow Applied to Lamotrigine

Current methods to assess risk in infants exposed to maternal medication through breast milk do not specifically account for infants most vulnerable to high drug exposure. A workflow applied to lamotrigine incorporated variability in infant anatomy and physiology, milk intake volume, and milk concentration to predict infant exposure. An adult physiologically based pharmacokinetic model of lamotrigine was developed and evaluated. The model was scaled to account for growth and maturation of a virtual infant population (n=100). Daily infant doses were simulated using milk intake volume and concentration models described by a nonlinear equation of weight-normalized intake across infant age and a linear function on the relationship of observed milk concentrations and maternal doses, respectively. Average infant plasma concentration at steady state was obtained through simulation. Models were evaluated by comparing observed to simulated infant plasma concentrations from breastfeeding infants based on a 90% prediction interval (PI). Upper AUC ratio (UAR) was defined as a novel risk metric. Twenty-five paired (milk concentrations measured) and 18 unpaired (milk concentrations unknown) infant plasma samples were retrieved from the literature. Forty-four percent and 11% of the paired and unpaired infant plasma concentrations were outside of the 90% PI, respectively. Over all ages (0-7 months), unpaired predictions captured more observed infant plasma concentrations within 90% PI than paired. UAR was 0.18-0.44 when mothers received 200 mg lamotrigine, suggesting that infants can receive 18-44% of the exposure per dose as compared to adults. UARs determined for further medications could reveal trends to better classify at-risk mother-infant pairs.

A repository of protein abundance data of drug metabolizing enzymes and transporters for applications in physiologically based pharmacokinetic (PBPK) modelling and simulation

Population factors such as age, gender, ethnicity, genotype and disease state can cause inter-individual variability in pharmacokinetic (PK) profile of drugs. Primarily, this variability arises from differences in abundance of drug metabolizing enzymes and transporters (DMET) among individuals and/or groups. Hence, availability of compiled data on abundance of DMET proteins in different populations can be useful for developing physiologically based pharmacokinetic (PBPK) models. The latter are routinely employed for prediction of PK profiles and drug interactions during drug development and in case of special populations, where clinical studies either are not feasible or have ethical concerns. Therefore, the main aim of this work was to develop a repository of literature-reported DMET abundance data in various human tissues, which included compilation of information on sample size, technique(s) involved, and the demographic factors. The collation of literature reported data revealed high inter-laboratory variability in abundance of DMET proteins. We carried out unbiased meta-analysis to obtain weighted mean and percent coefficient of variation (%CV) values. The obtained %CV values were then integrated into a PBPK model to highlight the variability in drug PK in healthy adults, taking lamotrigine as a model drug. The validated PBPK model was extrapolated to predict PK of lamotrigine in paediatric and hepatic impaired populations. This study thus exemplifies importance of the DMET protein abundance database, and use of determined values of weighted mean and %CV after meta-analysis in PBPK modelling for the prediction of PK of drugs in healthy and special populations.

Lamotrigine pharmacokinetics following oral and stable-labeled intravenous administration in young and elderly adult epilepsy patients: Effect of age

OBJECTIVE

The objectives of this study were to investigate the effect of age on pharmacokinetic parameters of lamotrigine (LTG) and estimate parameter variability.

METHODS

Patients (>18 years old) who were already on a steady-state dose of LTG therapy with no interacting comedications were enrolled. Patients with significant cardiac disease, severe kidney dysfunction, or moderate-to-severe liver dysfunction were excluded. Fifty milligrams of a stable-labeled intravenous LTG formulation (SL-LTG) replaced 50 mg of a patient's normal daily oral LTG dose. Thirteen blood samples were collected in each person over 96 hours. SL-LTG and unlabeled LTG concentrations were measured simultaneously by gas chromatography-mass spectrometry. Concentration-time data were analyzed by nonlinear mixed-effects modeling (NONMEM version 7.3).

RESULTS

Twenty-eight patients representing 16 young (18-48 years old) and 12 elderly (63-87 years old) patients were included, yielding 382 unlabeled and 351 SL-LTG concentrations. A two-compartment model with first-order absorption and elimination adequately described the plasma concentration-time data. Bioavailability of oral LTG was approximately 74% and did not differ by age. LTG clearance was 27.2% lower in elderly than in young patients (1.80 L/h for a 70-kg patient).

SIGNIFICANCE

Although LTG bioavailability was not affected by age, LTG clearance was 27.2% lower in elderly versus young patients of comparable body weight, possibly indicating lower dosages being needed in this population.

Pharmacokinetics of lamotrigine and its metabolite N-2-glucuronide: Influence of polymorphism of UDP-glucuronosyltransferases and drug transporters

AIMS

This study aimed to develop a population pharmacokinetic model for quantitative evaluation of the influence of genetic variants in metabolic enzymes and transporters on lamotrigine pharmacokinetics while taking into account the influence of various clinical, biochemical and demographic factors.

METHODS

We included 100 patients with epilepsy on stable dosing with lamotrigine as mono or adjunctive therapy. Lamotrigine and lamotrigine N-2-glucuronide concentrations were determined in up to two plasma samples per patient. Patients were genotyped for UGT1A4, UGT2B7, ABCB1 and SLC22A1. Population pharmacokinetic analysis was performed by non-linear mixed effects modelling. Prior knowledge from previous pharmacokinetic studies was incorporated to stabilize the modelling process. A parent-metabolite model was developed to get a more detailed view on the covariate effects on lamotrigine metabolism.

RESULTS

With a base model absorption rate (interindividual variability) was estimated at 1.96 h(-1) (72.8%), oral clearance at 2.32 l h(-1) (41.4%) and distribution volume at 77.6 l (30.2%). Lamotrigine clearance was associated with genetic factors, patient's weight, renal function, smoking and co-treatment with enzyme inducing or inhibiting drugs. In patients with UGT2B7-161TT genotype clearance was lower compared with GT and GG genotypes. Clearance was particularly high in patients with UGT2B7 372 GG genotype (compared with AA genotype it was 117%; 95% CI 44.8, 247% higher).

CONCLUSIONS

Variability in lamotrigine pharmacokinetics is large and quantification of its sources may lead to more precise individual treatment. Genotyping for UGT2B7 may be useful in various clinical settings.

Intravenous and Intramuscular Formulations of Antiseizure Drugs in the Treatment of Epilepsy

Intravenous and intramuscular antiseizure drugs (ASDs) are essential in the treatment of clinical seizure emergencies as well as in replacement therapy when oral administration is not possible. The parenteral formulations provide rapid delivery and complete (intravenous) or nearly complete (intramuscular) bioavailability. Controlled administration of the ASD is feasible with intravenous but not intramuscular formulations. This article reviews the literature and discusses the chemistry, pharmacology, pharmacokinetics, and clinical use of currently available intravenous and intramuscular ASD formulations as well as the development of new formulations and agents. Intravenous or intramuscular formulations of lorazepam, diazepam, midazolam, and clonazepam are typically used as the initial treatment agents in seizure emergencies. Recent studies also support the use of intramuscular midazolam as easier than the intravenous delivery of lorazepam in the pre-hospital setting. However, benzodiazepines may be associated with hypotension and respiratory depression. Although loading with intravenous phenytoin was an early approach to treatment, it is associated with cardiac arrhythmias, hypotension, and tissue injury at the injection site. This has made it less favored than fosphenytoin, a water-soluble, phosphorylated phenytoin molecule. Other drugs being used for acute seizure emergencies are intravenous formulations of valproic acid, levetiracetam, and lacosamide. However, the comparative effectiveness of these for status epilepticus (SE) has not been evaluated adequately. Consequently, guidelines for the medical management of SE continue to recommend lorazepam followed by fosphenytoin, or phenytoin if fosphenytoin is not available. Intravenous solutions for carbamazepine, lamotrigine, and topiramate have been developed but remain investigational. The current ASDs were not developed for use in emergency situations, but were adapted from ASDs approved for chronic oral use. New approaches for bringing drugs from experimental models to treatment of human SE are needed.

Use of Antiepileptic Drugs in Patients with Chronic Kidney Disease and End Stage Renal Disease

Epilepsy is a disorder with an approximate worldwide prevalence of 1%. Due to complexities of metabolism, protein-binding, renal elimination, and other pharmacokinetic parameters, the dosing of antiepileptic drugs (AEDs) in patients with chronic kidney disease (CKD) or end stage renal disease (ESRD) deserves special attention. This is a review of the most commonly prescribed AEDs with special focus on their indication, pharmacokinetics, and unique considerations for use in patients with CKD and ESRD. A review of their renal toxicities is also included.

Pharmacokinetic of antiepileptic drugs in patients with hepatic or renal impairment

Many factors influence choice of antiepileptic drugs (AEDs), including efficacy of the drug for the indication (epilepsy, neuropathic pain, affective disorder, migraine), tolerability, and toxicity. The first-generation AEDs and some newer AEDs are predominately eliminated by hepatic metabolism. Other recent AEDs are eliminated by renal excretion of unchanged drug or a combination of hepatic metabolism and renal excretion. The effect of renal and hepatic disease on the dosing will depend on the fraction of the AED eliminated by hepatic and/or renal excretion, the metabolic isozymes involved, as well as the extent of protein binding, if therapeutic drug monitoring is used. For drugs that are eliminated by renal excretion, methods of estimating creatinine clearance can be used to determine dose adjustments. For drugs eliminated by hepatic metabolism, there are no specific markers of liver function that can be used to provide guidance in dosage adjustments. Based on studies with probe drugs, the hepatic metabolic enzymes are differentially affected depending on the cause and severity of hepatic disease, which can aid in predicting dose adjustment when clinical data are not available. Several AEDs are also associated with laboratory markers of mild hepatic dysfunction and, rarely, more severe hepatic injury. In contrast, the risk of renal injury from AEDs is generally low. In general, co-morbid hepatic or renal diseases influence the decision for the selection of an AED. For some patients dosing changes to their existing AEDs may be appropriate. For others, a change to another AED may be a better option.

Lamotrigine and its applications in the treatment of epilepsy and other neurological and psychiatric disorders

Lamotrigine is a broad-spectrum antiepileptic drug, initially approved in 1994 for the adjunctive treatment of partial seizures in adults and for the generalized seizures of Lennox-Gastaut syndrome in pediatric (>2 years old) and adult populations. Its role in the treatment of bipolar disorder type I has also been well established. In addition, lamotrigine has been successfully used for the management of other neurological conditions such as migraines and neuropathic pain, and preliminary data show promising results. It has favorable pharmacokinetic properties and is generally well tolerated. The small risk of serious skin rash can be minimized with slow titration of the drug and dose adjustment with concomitant medications. Lamotrigine has demonstrated particular benefit in the treatment of women and elderly patients with epilepsy.

Use of antiepileptic drugs in hepatic and renal disease

The use of antiepileptic drugs in patients with renal or hepatic disease is common in clinical practice. Since the liver and kidney are the main organs involved in the elimination of most drugs, their dysfunction can have important effects on the disposition of antiepileptic drugs. Renal or hepatic disease can prolong the elimination of the parent drug or an active metabolite leading to accumulation and clinical toxicity. It can also affect the protein binding, distribution, and metabolism of a drug. The protein binding of anionic acidic drugs, such as phenytoin and valproate, can be reduced significantly by renal failure, causing difficulties in the interpretation of total serum concentrations commonly used in clinical practice. Dialysis can further modify the pharmacokinetic parameters or result in significant removal of the antiepileptic drugs. Antiepileptic drugs that are eliminated unchanged by the kidneys or undergo minimal metabolism include gabapentin, pregabalin, vigabatrin, and topiramate when used as monotherapy. Drugs eliminated predominantly by biotransformation include phenytoin, valproate, carbamazepine, tiagabine, and rufinamide. Drugs eliminated by a combination of renal excretion and biotransformation include levetiracetam, lacosamide, zonisamide, primidone, phenobarbital, ezogabine/retigabine, oxcarbazepine, eslicarbazepine, ethosuximide, and felbamate. Drugs in the latter group can be used cautiously in patients with either renal or liver failure. Antiepileptic drugs that are at high risk of being extracted by hemodialysis include ethosuximide, gabapentin, lacosamide, levetiracetam, pregabalin and topiramate. The use of antiepileptic drugs in the presence of hepatic or renal disease is complex and requires great familiarity with the pharmacokinetics of these agents. Closer follow-up of the patients and more frequent monitoring of serum concentrations are required to optimize clinical outcomes.

Lamotrigine and hemodialysis in bipolar disorder: case analysis of dosing strategy with literature review

OBJECTIVE

Medical conditions and associated procedures/treatments may impact therapeutic blood levels of pharmacologic agents in the illnesses we treat. The use of anti-epileptic drugs in the treatment of psychiatric disorders, most commonly bipolar disorders, and epilepsy is a case in point. This report addresses the impact of hemodialysis on lamotrigine efficacy in bipolar disorder.

METHOD

Case analysis with literature review.

RESULTS

A bipolar disorder patient stabilized on lamotrigine 200 mg total daily dose was admitted to the hospital with end-stage renal disease. With three consecutive days of hemodialysis, treatment-emergent hypomanic features were noted by the patient and confirmed in psychiatric consultation. When lamotrigine was increased to 250 mg total daily dose, the bipolar features remitted.

CONCLUSION

Lamotrigine titration may be required in bipolar disorder patients undergoing hemodialysis secondary to the associated hemodialysis extraction factor. Therapeutic drug monitoring is recommended in these patients.

Randomized double-blind study comparing the efficacy and safety of lamotrigine and amitriptyline in painful diabetic neuropathy

AIMS

To compare the efficacy and safety of lamotrigine and amitriptyline in controlling chronic painful peripheral neuropathy in diabetic patients.

METHODS

A randomized, double-blind, crossover, active-control, clinical trial with variable dose titration was carried out (n = 53). Amitriptyline orally, at doses of 10, 25 and 50 mg at night-time, each dose for 2 weeks, and lamotrigine orally, at doses of 25, 50 and 100 mg twice daily, each dose for 2 weeks, by optional titration were used. There was a placebo washout period for 2 weeks between the two drugs. Assessment for pain relief, overall improvement and adverse events were carried out.

RESULTS

Good, moderate and mild pain relief were noted in 19 (41%), six (13%) and seven (15%) patients on lamotrigine and 13 (28%), five (11%) and 15 (33%) patients on amitriptyline, respectively, by patient's global assessment of efficacy and safety. Patient and physicians global assessment, McGill pain questionnaire and Likert pain scale showed no significant difference between the treatments, although improvement with both treatments was seen from 2 weeks. Of the 44 adverse events reported, 33 (75%) were with amitriptyline, sedation being the commonest [in 19 (43%) patients]. Lamotrigine caused adverse events in 11 (25%), of which rash in three (7%) and elevations of creatinine in four (9%) were the most common. The preferred lamotrigine dose was 25 mg twice daily.

CONCLUSIONS

As there are few differences between the two treatments in efficacy, lamotrigine 25 mg twice daily might be the first choice as it is associated with fewer adverse effects in our population.

Use of Antiepileptic Drugs in Patients with Kidney Disease

The number of medications used to treat different types of seizures has increased over the last 10-15 years. Most of the newer antiepileptic drugs (AEDs) are likely to be unfamiliar to many nephrologists. For both the older and newer AEDs, basic pharmacokinetic information, recommendations for drug dosing in patients with reduced kidney function or who are on dialysis, and adverse renal and fluid-electrolyte effects are reviewed. Newer AEDs are less likely to have significant drug-drug interactions than older agents, but are more likely to need dosage adjustment in patients with reduced kidney function. The most common renal toxicities of these drugs include metabolic acidosis, hyponatremia, and nephrolithiasis; interstitial nephritis and other adverse effects are less common. Little is known about the clearance of most of the newer AEDs with high-efficiency hemodialyzers or with peritoneal dialysis. Monitoring of drug levels when available, careful clinical assessment of patients taking AEDs, and close collaboration with neurologists is essential to the management of patients taking AEDs.

Lamotrigine in the treatment of bipolar disorder

Lamotrigine is a novel anticonvulsant agent that has recently been introduced as a long-term treatment in bipolar disorder. Its role in the treatment of epilepsy is based on its actions to decrease ion channel conductance and antagonise glutamatergic function. Therefore, it has a mode of action unlike other agents used on a long-term basis in mood disorders. The evidence for efficacy is stronger for the prevention of depressive, rather than manic, episodes. The pivotal trials are in bipolar I disorder, but there is interest in its actions in patients with bipolar II and spectrum conditions. Its efficacy in other psychiatric conditions remains to be properly established. It is well tolerated and, with careful prescribing, the incidence of rash occurs no more than with placebo; however this is still a concern. Although usually well tolerated, headache, insomnia and drowsiness are probably the most common side effects.

Glucuronidation in therapeutic drug monitoring

BACKGROUND

Glucuronidation is a major drug-metabolizing reaction in humans. A pharmacological effect of glucuronide metabolites is frequently neglected and the value of therapeutic drug monitoring has been questioned. However, this may not always be true.

METHODS

In this review the impact of glucuronidation on therapeutic drug monitoring has been evaluated on the basis of a literature search and experience from the own laboratory.

RESULTS

The potential role of monitoring glucuronide metabolite concentrations to optimize therapeutic outcome is addressed on the basis of selected examples of drugs which are metabolized to biologically active/reactive glucuronides. Furthermore indirect effects of glucuronide metabolites on parent drug pharmacokinetics are presented. In addition, factors that may modulate the disposition of these metabolites (e.g. genetic polymorphisms, disease processes, age, and drug-drug interactions) are briefly mentioned and their relevance for the clinical situation is critically discussed.

CONCLUSION

Glucuronide metabolites can have indirect as well as direct pharmacological or toxicological effects. Although convincing evidence to support the introduction of glucuronide monitoring into clinical practice is currently missing, measurement of glucuronide concentrations may be advantageous in specific situations. If the glucuronide metabolite has an indirect effect on the pharmacokinetics of the parent compound, monitoring of the parent drug may be considered. Furthermore pharmacogenetic approaches considering uridine diphosphate (UDP) glucuronosyltransferases polymorphisms may become useful in the future to optimize therapy with drugs subject to glucuronidation.

Lamotrigine for bipolar disorder: translating research into clinical practice

Lamotrigine (Lamictal, GlaxoSmithKline) is a recently developed anticonvulsant which has been investigated for efficacy in bipolar disorder. Increasing evidence indicates that it may have a different therapeutic profile than more established first-line mood stabilizers such as lithium and valproate. In particular, evidence from well-designed trials suggests efficacy for acute management and prophylaxis of bipolar depression but not mania. However, clinically relevant drug interactions and side effects can occur with lamotrigine, including benign to serious rash. The objectives of this drug profile are to review the basic chemical and pharmacological characteristics of lamotrigine, critically examine the growing body of research literature on its clinical use in the treatment of bipolar disorder, and review the safety and tolerability of lamotrigine as well as drug interactions relevant to clinical practice. Practical recommendations regarding titration and the management of rash are offered.

Lamotrigine in psychiatry: pharmacology and therapeutics

Following the introduction of lamotrigine in 1994 as a treatment for epilepsy in the United States, the drug has seen progressively greater application in psychiatry, particularly as a treatment for bipolar disorder. This review critically evaluates the support for lamotrigine use across a broad range of psychiatric disorders as well as discuss its pharmacology, side-effect profile, and interactions with other medications.

Special considerations in the treatment of patients with bipolar disorder and medical co-morbidities

BACKGROUND: The pharmacological treatment of bipolar disorder has dramatically improved with multiple classes of agents being used as mood-stabilizers, including lithium, anticonvulsants, and atypical antipsychotics. However, the use of these medications is not without risk, particularly when a patient with bipolar disorder also has comorbid medical illness. As the physician who likely has the most contact with patients with bipolar disorder, psychiatrists must have a high index of suspicion for medical illness, as well as a basic knowledge of the risks associated with the use of medications in this patient population. METHODS: A review of the literature was conducted and papers addressing this topic were selected by the authors. RESULTS AND DISCUSSION: Common medical comorbidities and treatment-emergent illnesses, including obesity, diabetes mellitus, dyslipidemia, cardiac disease, hepatic disease, renal disease, pulmonary disease and cancer are reviewed with respect to concomitant use of mood stabilizers. Guidance to clinicians regarding effective monitoring and treatment is offered. CONCLUSIONS: Mood-stabilizing medications are necessary in treating patients with bipolar disorder and often must be used in the face of medical illness. Their safe use is possible, but requires increased vigilance in monitoring for treatment-emergent illnesses and effects on comorbid medical illness.

Lamotrigine: a review of its use in bipolar disorder

Lamotrigine (Lamictal), a phenyltriazine derivative, is a well established anticonvulsant agent that has shown efficacy in the prevention of mood episodes in adult patients with bipolar I disorder. The mechanism of action of the drug in patients with bipolar disorder may be related to the inhibition of sodium and calcium channels in presynaptic neurons and subsequent stabilisation of the neuronal membrane. Lamotrigine monotherapy significantly delayed time to intervention with additional pharmacotherapy or electroconvulsive therapy for any new mood episode (mania, hypomania, depression and mixed episodes), compared with placebo, in two large, randomised, double-blind trials of 18 months' duration. Additionally, lamotrigine was significantly superior to placebo at prolonging time to intervention for depression. These effects of lamotrigine were demonstrated in both recently manic/hypomanic and recently depressed patients. Lamotrigine showed efficacy in delaying manic/hypomanic episodes in pooled data only, although lithium was superior to lamotrigine on this measure. Two of four double-blind, short-term studies have shown lamotrigine to be more effective than placebo in the treatment of patients with treatment-refractory bipolar disorder or those with bipolar depression. Lamotrigine has not demonstrated efficacy in the treatment of acute mania. Lamotrigine was generally well tolerated in maintenance studies with the most common adverse events being headache, nausea, infection and insomnia. Incidences of diarrhoea and tremor were significantly lower in lamotrigine- than in lithium-treated patients. The incidence of serious rash with lamotrigine treatment was 0.1% in all studies of bipolar disorder and included one case of mild Stevens-Johnson syndrome. Lamotrigine did not appear to cause bodyweight gain. The dosage of lamotrigine is titrated over a 6-week period to 200 mg/day to minimise the incidence of serious rash. Adjustments to the initial and target dosages are required if coadministered with valproate semisodium or carbamazepine.

CONCLUSION

Lamotrigine has been shown to be an effective maintenance therapy for patients with bipolar I disorder, significantly delaying time to intervention for any mood episode. Additionally, lamotrigine significantly delayed time to intervention for a depressive episode and showed limited efficacy in delaying time to intervention for a manic/hypomanic episode, compared with placebo. Although not approved for the short-term treatment of mood episodes, lamotrigine has shown efficacy in the acute treatment of patients with bipolar depression but has not demonstrated efficacy in the treatment of acute mania. Lamotrigine is generally well tolerated, does not appear to cause bodyweight gain and, unlike lithium, generally does not require monitoring of serum levels.

Children versus adults: pharmacokinetic and adverse-effect differences

Pharmacokinetic differences may play a part in the age-related differences in the incidence of adverse effects. The most common idiosyncratic reaction to lamotrigine (LTG) is rash, affecting 10-20% of patients. Risk factors are young age, concurrent valproate (VPA), high starting dose, and rapid escalation. In children, cytochrome P450 (CYP)-catalyzed metabolism is increased, and uridine diphosphate (UDP)-glucuronosyltransferase (UGT)-catalyzed metabolism is not significantly different from that in adults. A CYP-catalyzed arene oxide intermediate of LTG has been identified. The increase CYP metabolism of LTG in children could result in increased formation of the reactive metabolite and a higher incident of rash. Children often received higher milligram per kilogram doses compared with adults. The higher dose would cause an increased amount of LTG metabolized to the reactive arene oxide intermediate. VPA therapy is associated with a transient elevation in liver-function tests in 15-30% of patients and a rare, fatal hepatotoxicity. Most cases of VPA hepatotoxicity occurred in children younger than 2 years who had preexisting neurologic or other physical defects. Hypotheses regarding the pathogenesis of the hepatotoxicity include preexisting mitochondrial disease or inborn errors of metabolism, VPA inhibition of beta-oxidation, and toxicity from VPA metabolites VPA, 4-ene-VPA, and 2,4-diene-VPA. Infants and children have higher concentration ratios of 4-ene-VPA to VPA. Polytherapy with enzyme inducers increases the formation of the hepatotoxic metabolites. The role of underlying metabolic disorders associated with hepatodegeneration and intractable seizures without VPA is a major confounder in identifying risk factors and demonstrates the difficulty in separating underlying disease factors in rare idiosyncratic reactions.

Lamotrigine update and its use in mood disorders

OBJECTIVE

To provide a qualitative, systematic update and review of the pharmacology, pharmacokinetics, efficacy in mood disorders, adverse effects, and costs of lamotrigine.

DATA SOURCES

Citations obtained from MEDLINE searches (1985-September 2001) using lamotrigine as a text word, articles identified in reference lists of pertinent articles, abstracts presented at conferences, and research data from GlaxoSmithKline.

DATA EXTRACTION

English-language articles were considered for possible inclusion. Each title and abstract was examined to determine whether the publication contained up-to-date information relevant to the objective. Twenty clinical trials that provided data on response rates in mood disorders were tabulated.

DATA SYNTHESIS

Lamotrigine's primary action is to modulate voltage-gated sodium channels. Evidence suggests that it decreases glutamate transmission, directly reduces calcium influx, mildly blocks transmitter reuptake, and alters intracellular mechanisms of resting transmitter release. The average half-life of lamotrigine is approximately 24 hours, but decreases to approximately 7.4 hours when used concurrently with phenytoin, and increases to approximately 59 hours with valproic acid. Seven of the 20 clinical trials were randomized, double-blind, and controlled. Existing data are inadequate to evaluate lamotrigine use in major depression. The pooled response rates for patients with depressed, manic, mixed, and rapid cycling bipolar disorder were similar, ranging from 52% to 63%. Adverse effects are infrequent when the drug is used alone, but become more frequent when lamotrigine is combined with other anticonvulsants. While most rashes are mild, approximately 1 in 500 patients develops exfoliative dermatitis. A slow upward dose titration is recommended to reduce the incidence of serious rash, but this may delay the attainment of adequate dosage for 6 weeks. Lamotrigine has positive effects on cognitive function, but occasionally produces insomnia. Lamotrigine costs 2-4 times more than lithium, carbamazepine, and generic valproic acid.

CONCLUSIONS

When efficacy, adverse effects, and cost are considered, lamotrigine should probably be reserved as a second-line agent for bipolar depression.

Strategies for optimizing antiepileptic drug therapy in elderly people

The elderly take more antiepileptic drugs (AEDs) than all other adults. This extensive use directly correlates with an increased prevalence of epilepsy in a growing population of older people, as well as other neuropsychiatric conditions such as neuropathic pain and behavioral disorders associated with dementia and for which AEDs are administered. The agents account for nearly 10% of all adverse drug reactions in the elderly and are the fourth leading cause of adverse drug reactions in nursing home residents. Numerous factors associated with advanced age contribute to the high frequency of untoward drug effects in this population; however, strategies are available to ensure optimal outcomes.

Treating epilepsy in the elderly: safety considerations

The incidence of epilepsy increases with advancing age. Epilepsy in the elderly has different aetiologies from that in younger populations, cerebrovascular disease being the most common condition associated with seizures. Partial seizures are the predominant seizure type in older patients. A diagnosis of epilepsy in the elderly is based mainly on the history and is frequently delayed. In addition, seizure imitators are especially frequent. In many cases ancillary tests for diagnosis may show normal age-related variants, sometimes making results difficult to interpret. Treating epilepsy in the elderly is problematic due to a number of issues that relate to age and comorbidity. The physical changes associated with increasing age frequently lead to changes in the pharmacokinetics of many anticonvulsants. The treatment of epilepsy in the elderly is also complicated by the existence of other diseases that might affect the metabolism or excretion of anticonvulsants and the presence of concomitant medications that might interact with them. Moreover, specific trials of anticonvulsants in the aged population are scarce. General guidelines for treatment include starting at lower doses, slowing the titration schedule, individualising the choice of anticonvulsant to the characteristics of the patient, avoiding anticonvulsants with important cognitive or sedative adverse effects, and where possible, treating with monotherapy.

Human variability in glucuronidation in relation to uncertainty factors for risk assessment

The appropriateness of the default uncertainty factor for human variability in kinetics has been investigated for glucuronidation using an extensive database of substrates metabolised primarily by this pathway. Inter-individual variability was quantified for 15 compounds from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups using parameters relating to chronic exposure (metabolic and total clearances, area under the plasma concentration time-curve (AUC)) and acute exposure (C(max)). Low inter-individual variability (about 30-35%) was found for all parameters (clearance corrected or not corrected for body weight, metabolic clearance, oral AUC and C(max)) after either iv or oral administration to healthy adults. The overall variability of 31% for glucuronidation in healthy adults supported the validity of the default kinetic uncertainty factor of 3.16 for this group, because it would cover more than 99% of individuals. Comparisons between potentially sensitive subgroups and healthy adults using differences in means and variability indicated that neonates showed the greatest impairment of glucuronidation, and that the 3.16 kinetic default factor applied to the mean data for adults would be inadequate for this subpopulation. The in vivo data have been used to derive pathway-related default factors for compounds eliminated largely via glucuronidation.

Population pharmacokinetics of lamotrigine

The present study estimated the population pharmacokinetics of lamotrigine in patients receiving oral lamotrigine therapy with drug concentration monitoring, and determined intersubject and intrasubject variability. A total of 129 patients were analyzed from two clinical sites. Of these, 124 patients provided sparse data (198 concentration-time points); nine patients (four from a previous group plus five from the current group) provided rich data (431 points). The population analysis was conducted using P-PHARM (SIMED Scientific Software, Cedex, France), a nonlinear mixed-effect modeling program. A single exponential elimination model (first-order absorption) with heteroscedastic weighting was used. Apparent clearance (CL/F) and volume of distribution (V/F) were the pharmacokinetic parameters estimated. Covariate analysis was performed to determine which factors explained any of the variability associated with lamotrigine clearance. Population estimates of CL/F and V/F for lamotrigine generated in the final model were 2.14 +/- 0.81 L/h and 78.1 +/- 5.1 L/kg. Intersubject and intrasubject variability for clearance was 38% and 38%, respectively. The covariates of concomitant valproate and phenytoin therapy accounted for 42% of the intersubject variability of clearance. Age, gender, clinic site, and other concomitant antiepileptic drugs did not influence clearance. This study of the population pharmacokinetics of lamotrigine in patients using the drug clinically provides useful data and should lead to better dosage individualization for lamotrigine.

Lamotrigine

Lamotrigine is a newly available antiepileptic drug with a broad spectrum of efficacy and a tolerability profile that is favorable for use in many patients. Problems with rash are related to rate of dose ascension and drug interactions with valproate. Efficacy in treatment of mood disorder and some pain syndromes will broaden the use of this unique compound.

Pharmacologic management of epilepsy in the elderly

OBJECTIVE

To review the epidemiology and pharmacologic management of epilepsy in elderly patients.

DATA SOURCES

Controlled trials, case studies, and review articles identified via MEDLINE using the search terms epilepsy, seizures, elderly, phenobarbital, primidone, phenytoin, carbamazepine, valproic acid, felbamate, gabapentin, lamotrigine, topiramate, tiagabine, levetiracetam, oxcarbazepine, and zonisamide. Recently published standard textbooks on epilepsy were also consulted.

DATA SYNTHESIS

Epilepsy is a common neurologic disorder in the elderly. Cerebrovascular and neurodegenerative diseases are the most common causes of new-onset seizures in these patients. Alterations in protein binding, distribution, elimination, and increased sensitivity to the pharmacodynamic effects of antiepileptic drugs (AEDs) are relatively frequent, and these factors should be assessed at the initiation, and during adjustment, of treatment. Drug-drug interactions are also an important issue in elderly patients, because multiple drug use is common and AEDs are susceptible to many interactions. In addition to understanding age-related changes in the pharmacokinetics and pharmacodynamics of AEDs, clinicians should know the common seizure types in the elderly and the spectrum of AED activity for these seizure types. AEDs with activity against both partial-onset and generalized seizures include felbamate, lamotrigine, levetiracetam, topiramate, valproic acid, and zonisamide. Other AEDs discussed in this review (carbamazepine, gabapentin, phenobarbital, phenytoin, primidone, and tiagabine) are most useful for partial-onset seizures.

CONCLUSION

The provision of safe and effective drug therapy to elderly patients requires an understanding of the unique age-related changes' in the pharmacokinetics and pharmacodynamics of AEDs as well as an appreciation of common seizure types and the drugs that are effective for the specific types seen in the elderly.