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

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.

Interactions of stiripentol with clobazam and valproate in the mouse maximal electroshock-induced seizure model

The aim of this study was to characterize the anticonvulsant effects of stiripentol (STP) in combination with clobazam [CLB], and valproate [VPA]) in the mouse maximal electroshock (MES)-induced seizure model using the type I isobolographic analysis for parallel and non-parallel dose-response relationship curves (DRRCs). Potential adverse-effect profiles of interactions of STP with CLB and VPA at the fixed-ratio of 1:1 in the MES test with respect to motor performance, long-term memory and skeletal muscular strength were measured along with total brain antiepileptic drug concentrations. In the mouse MES model, STP administered singly had its DRRC non-parallel to that for CLB and, simultaneously, parallel to that for VPA. With type I isobolography for parallel DRRCs, the combinations of STP with VPA at three fixed-ratios of 1:3, 1:1 and 3:1 exerted sub-additive (antagonistic) interaction. Isobolography for non-parallel DRRCs revealed that the combination of STP with CLB at the fixed-ratio of 1:1 produced additive interaction. For all combinations, neither motor coordination, long-term memory nor muscular strength was affected. Total brain antiepileptic drug concentrations revealed bi-direction changes with the most profound being an 18.6-fold increase in CLB by STP and a 2.3-fold increase in STP by VPA. In conclusion, the additive interaction between STP and CLB was associated with a concurrent pharmacokinetic interaction and these data may explain the clinical efficacy seen with this combination. In contrast, the antagonism between STP and VPA was surprising since synergism is observed clinically.

Relationship between adverse effects of antiepileptic drugs, number of coprescribed drugs, and drug load in a large cohort of consecutive patients with drug-refractory epilepsy

PURPOSE

To evaluate the adverse effects (AEs) of antiepileptic drugs (AEDs) in adults with refractory epilepsy and their relationship with number of coprescribed AEDs and AED load.

METHODS

Patients with refractory epilepsy were enrolled consecutively at 11 tertiary referral centers. AEs were assessed through unstructured interview and the Adverse Event Profile (AEP) questionnaire. AED loads were calculated as the sum of prescribed daily dose (PDD)/defined daily dose (DDD) ratios for each coprescribed AED.

RESULTS

Of 809 patients enrolled, 709 had localization-related epilepsy and 627 were on polytherapy. AED loads increased with increasing number of AEDs in the treatment regimen, from 1.2 +/- 0.5 for patients on monotherapy to 2.5 +/- 1, 3.7 +/- 1.1, and 4.7 +/- 1.1 for those on two, three, and > or =4 AEDs, respectively. The number of spontaneously reported AEs correlated with the number of AEs identified by the AEP (r = 0.27, p < 0.0001). AEP scores did not differ between patients with monotherapy and patients with polytherapy (42.8 +/- 11.7 vs. 42.6 +/- 11.2), and there was no correlation between AEP scores and AED load (r = -0.05, p = 0.16).

CONCLUSIONS

AEs did not differ between monotherapy and polytherapy patients, and did not correlate with AED load, possibly as a result of physicians' intervention in individualizing treatment regimens. Taking into account the limitations of a cross-sectional survey, these findings are consistent with the hypothesis that AEs are determined more by individual susceptibility, type of AEDs used, and physicians' skills, than number of coprescribed AEDs and AED load.

Review of topiramate for the treatment of epilepsy in elderly patients

Individuals over 65 years of age experience the new onset of seizures at a prevalence rate of roughly twice that of younger adults. Differences in physiology, need of concomitant medications, and liability for cognitive deficits in this population, make the choice of anticonvulsant drugs especially important. This paper reviews topiramate (TPM), a treatment for many types of seizures, with the above risks in mind. In particular, we discuss efficacy and pharmacokinetics with emphasis on the older patient, and adverse events in both the younger and older adult. With most studies of TPM-induced cognitive deficits having been performed in younger adults and volunteers, we discuss the implications for the older adult. Even in studies of younger individuals, up to 50% discontinue TPM because of intolerable cognitive deficits. Most studies find specific declines in working memory and verbal fluency. In conclusion, we give recommendations for use of this antiepileptic drug in this population.

Fluconazole-induced intoxication with phenytoin in a patient with ultra-high activity of CYP2C9

PURPOSE

The cytochrome P450 enzyme CYP2C9 metabolizes several important drugs, such as warfarin and oral antidiabetic drugs. The enzyme is polymorphic, and all known alleles, for example, CYP2C9*2 and*3, give decreased activity. Ultra-high activity of the enzyme has not yet been reported.

METHODS

We present a patient with Behçet's disease who required treatment with high doses of phenytoin. When fluconazole, a potent inhibitor of CYP2C9, was added to the treatment regimen, the patient developed ataxia, tremor, fatigue, slurred speech and somnolence, indicating phenytoin intoxication. On suspicion of ultra-high activity of CYP2C9, a phenotyping test for CYP2C9 with losartan was performed.

RESULTS

The patient was shown to have a higher activity of CYP2C9 than any of the 190 healthy Swedish Caucasians used as controls.

CONCLUSIONS

Our finding of an ultrarapid metabolism of losartan and phenytoin may apply to other CYP2C9 substrates, where inhibition of CYP2C9 may cause severe adverse drug reactions.

Generic products of antiepileptic drugs: a perspective on bioequivalence and interchangeability

Most antiepileptic drugs (AEDs) are currently available as generic products, yet neurologists and patients are reluctant to switch to generics. Generic AEDs are regarded as bioequivalent to brand AEDs after meeting the average bioequivalence criteria; consequently, they are considered to be interchangeable with their respective brands without loss of efficacy and safety. According to the U.S. Food and Drug Administration (FDA) the present bioequivalence requirements are already so rigorous and constrained that there is little possibility that generics that meet regulatory bioequivalence criteria could lead to therapeutic problems. So is there a scientific rationale for the concerns about switching patients with epilepsy to bioequivalent generics? Herein we discuss the assessment of bioequivalence and propose a scaled-average bioequivalence approach where scaling of bioequivalence is carried out based on brand lot-to-lot variance as an alternative to the conventional bioequivalence test as a means to determine whether switching patients to generic formulations, or vice versa, is a safe and effective therapeutic option. Meeting the proposed scaled-average bioequivalence requirements will ensure that when an individual patient is switched, he or she has fluctuations in plasma levels similar to those from lot-to-lot of the brand reference levels and thus should make these generic products safely switchable without change in efficacy and safety outcomes.

Comparison of a new serum topiramate immunoassay to fluorescence polarization immunoassay

Topiramate is a newer anticonvulsant used to treat epilepsy, migraines, bipolar disorder, posttraumatic stress, and other conditions. Serum topiramate concentrations are measured to determine optimal levels, address therapeutic failure or drug-drug interactions, and assess compliance. Two high-throughput assays for serum topiramate measurement were compared: the Seradyn fluorescence polarization immunoassay (FPIA) on an Abbott TDx/FLx instrument and a new immunoassay from ARK Diagnostics performed on an Olympus AU680 automated analyzer. Precision, linearity, limit of quantitation, carryover, spike recovery, and endogenous interferences were found to be acceptable for the ARK assay. These studies were complemented by comparison of 120 patient samples analyzed using both methods. The ARK immunoassay performed comparably to FPIA with minimal difference in serum topiramate concentrations within the therapeutic range (2.0-20 microg/mL). A slight systematic discordance was observed at higher concentrations (greater than 30 microg/mL) with ARK immunoassay results being on average 6% higher than FPIA. Thus, the ARK immunoassay appears to provide acceptable analytical performance and comparability to FPIA; furthermore, the assay is compatible with high-throughput autoanalyzers.

Management of antipsychotic and mood stabilizer medication in pregnancy: recommendations for antenatal care

The aim of the present study was to develop recommendations for antenatal care and monitoring for women with bipolar disorder and schizophrenia who are on lithium carbonate, antipsychotic or anti-epileptic medication during pregnancy. A literature search and review of original research, published reviews and guidelines was undertaken for mood stabilizers and antipsychotics in pregnancy and for the management of bipolar disorder and schizophrenia in pregnancy. This information was summarized, condensed and then reviewed by representatives of psychiatry, pharmacy, paediatrics and obstetrics to produce an information booklet and subsequently monitoring recommendations and tables. A model of antenatal monitoring and care for women with schizophrenia, bipolar disorder and related disorders who are maintained on psychotropic medication was developed. This included an online and published booklet for clinicians summarizing psychotropic medication in pregnancy, and lactation and monitoring tables that could be part of patient case files. These were to assist in reminding and educating staff on the need for additional monitoring and assessment above standard antenatal care for women on mood stabilizers and antipsychotic medication. Women with bipolar disorder and schizophrenia have an increased risk of complications in pregnancy from their illness and from the medications they are prescribed. A summary of the risks and a model of suggested additional monitoring during pregnancy have been developed in consultation across a number of clinical disciplines.

Selection of antiepileptic drugs in adults

Epilepsy affects approximately 50 million people worldwide, with an annual incidence of 50 to 70 cases per 100,000 population. The condition can strike at any time of life, with an immediate impact on everyday activities and routine. Key to optimal management is swift referral to an epilepsy specialist, appropriate investigation, and timely institution of antiepileptic drug therapy. In the past 20 years, the explosion of 13 new agents into the marketplace has greatly increased the potential for therapeutic intervention. This article explores the rationale for treatment selection in adults with epilepsy.

No pharmacokinetic interaction between lacosamide and carbamazepine in healthy volunteers

Lacosamide is a new antiepileptic drug for adjunctive treatment of adult partial-onset seizures. Two open-label, multiple-dose clinical trials were conducted to evaluate the potential for pharmacokinetic interaction between lacosamide and carbamazepine. The influence of carbamazepine on lacosamide pharmacokinetics (trial A) and lacosamide on carbamazepine pharmacokinetics (trial B) was investigated in 19 (trial A) and 18 (trial B) healthy male participants. Trial A participants received lacosamide 200 mg bid alone and with carbamazepine 200 mg bid. Trial B participants received carbamazepine 200 mg bid alone and with lacosamide 200 mg bid. Pharmacokinetic parameters, area under the concentration-time curve during a dosage interval at steady state (AUC(tau,ss)), and maximum steady-state plasma drug concentration during a dosage interval (C(max,ss)) of lacosamide, carbamazepine, and carbamazepine-10,11-epoxide were measured and compared for each drug alone and together. The AUC(tau,ss) and C(max,ss) point estimates (combined vs sole treatment) showed relative bioavailability of approximately 100% for both drugs. All 90% confidence intervals of AUC(tau,ss) and C(max,ss) were within the generally accepted bioequivalence ranges of 80% to 125%. No changes in rate or extent of absorption or terminal half-life were observed. These results suggest that lacosamide and carbamazepine have a low potential for pharmacokinetic drug-drug interaction in clinical use.

Topiramate concentrations in neonates treated with prolonged whole body hypothermia for hypoxic ischemic encephalopathy

PURPOSE

Therapeutic hypothermia reduces mortality and neurologic impairment in neonates with hypoxic-ischemic encephalopathy. Topiramate exerts a neuroprotective effect in asphyxiated neonatal animal models. However, no studies have investigated the association of hypothermia and topiramate, because topiramate pharmacokinetics during hypothermia and the optimal administration schedule are unknown. The influence of hypothermia on topiramate pharmacokinetics was evaluated in asphyxiated neonates treated with prolonged whole-body hypothermia and topiramate.

METHODS

Thirteen term newborns were treated with mild or deep whole body hypothermia for 72 h; all received oral topiramate, 5 mg/kg once a day for the first 3 days of life, and seven had concomitant phenobarbital treatment. Topiramate concentrations were measured on serial dried blood spots.

RESULTS

Topiramate concentrations were within the reference range in 11 of 13 newborns, whereas concentrations exceeded the upper limit in 2 of 13, both newborns on deep hypothermia. Topiramate concentrations reached a virtual steady state in nine newborns, for whom pharmacokinetic parameters were calculated. Values of topiramate maximal and minimal concentration, half-life, average concentration, and area under the time-concentration curve resulted in considerably higher values than those reported in normothermic infants. With respect to normothermic infants, time of maximal concentration was mildly delayed and apparent total body clearance was lower, suggesting slower absorption and elimination. Pharmacokinetic parameters did not differ significantly between infants on deep versus mild hypothermia and in those on topiramate monotherapy versus add-on phenobarbital.

CONCLUSION

Most neonates on prolonged hypothermia treated with topiramate 5 mg/kg once a day exhibited drug concentrations within the reference range for the entire treatment duration.

Consensus guidelines into the management of epilepsy in adults with an intellectual disability

BACKGROUND

Epilepsy has a pervasive impact on the lives of people with intellectual disability and their carers. The delivery of high-quality care is impacted on by the complexity and diversity of epilepsy in this population. This article presents the results of a consensus clinical guideline process.

RESULTS

A Delphi process identified a list of priority areas for the development of evidence-based guidelines. All guidelines were graded and consensus on scoring was achieved across the guideline group.

CONCLUSION

There is a dearth of high-quality evidence from well-constructed studies on which to base guidance. However, the development of internationally derived consensus guidelines may further support the management of epilepsy in adults with an intellectual disability.

A new rapid micromethod for the assay of phenobarbital from dried blood spots by LC-tandem mass spectrometry

Advantages of dried blood spot include low invasiveness, ease and low cost of sample collection, transport, and storage. We used tandem mass spectrometry (LC-MS/MS) to determine phenobarbital levels on dried blood spot specimens and compared this methodology to commercially available particle enhanced turbidimetric inhibition immunoassay (PETINIA) in plasma/serum samples. The calibration curve in matrix using D(5)-phenobarbital as internal standard was linear in the phenobarbital concentration range of 1-100 mg/L (correlation coefficient 0.9996). The coefficients of variation in blood spots ranged 2.29-6.71% and the accuracy ranged 96.54-103.87%. There were no significant differences between the concentrations measured using PETINA and LC-MS/MS (both had similar precision and accuracy) however, LC-MS/MS allows at least 1.5 times higher throughput of phenobarbital analysis and additionally offers ease of sample collection which is particularly important for newborns or small infants.

The management of epilepsy in pregnancy

While most women with epilepsy can expect a normal pregnancy outcome, epilepsy remains a significant contributor to both maternal and perinatal morbidity. Pre-pregnancy planning must address reliable contraception and optimisation of antiepileptic drug (AED) regimens to minimise teratogenic risk while maintaining seizure control. The most recent data from the AED registries regarding malformations is presented in this review, as is the limited data on the newer AEDs and studies linking neurocognitive outcomes to AED exposure. During pregnancy, important considerations include; therapeutic drug monitoring, surveillance for obstetric complications and vigilance for seizures during the intrapartum and postpartum period.

Pharmacological management of epilepsy: recent advances and future prospects

There is still a need for new antiepileptic drugs (AEDs) as the clinical efficacy, tolerability, toxicity or pharmacokinetic properties of existing AEDs may not be satisfactory. One new AED has recently been approved (rufinamide in 2007) and six others are in late-stage development (phase III and onwards) [brivaracetam, carisbamate, eslicarbazepine, lacosamide, retigabine and stiripentol]. The purpose of this review is to provide updated data on proposed mechanisms of action, efficacy and tolerability on these new AEDs, and to discuss the rationale for their development and possible advantages compared with existing treatment, based on recent publications and MEDLINE searches.Rufinamide, brivaracetam and stiripentol have been given the status of orphan drugs. Rufinamide was approved in Europe in 2007 for the use in Lennox-Gastaut syndrome. Brivaracetam has gained orphan status for development in progressive and symptomatic myoclonic seizures in Europe and the US, respectively. Stiripentol has gained orphan status in children with Dravet's syndrome and pharmaco-resistant epilepsy. All of these drugs demonstrate efficacy as adjunctive therapy in partial seizures. Three of the drugs are derivatives of existing AEDs: brivaracetam is a derivative of levetiracetam with improved affinity for the target molecule; carisbamate is a derivative of felbamate with improved tolerability; and eslicarbazepine is a derivative of carbamazepine with less interaction potential and no auto-induction. Lacosamide, retigabine, rufinamide and stiripentol are new compounds, unrelated to other AEDs.Further investigation and development of new broad-spectrum drugs is important for improved treatment of patients with epilepsy and other neurological and psychiatric disorders.