„Therapeutic drug monitoring“ in Epileptologie und Psychiatrie

Rapid determination of plasma vigabatrin by LC-ESI-MS/MS supporting therapeutic drug monitoring in children with infantile spasms

Vigabatrin is one of the second-generation anti-seizure medications (ASMs) designated orphan drugs by the FDA for monotherapy for pediatric patients with infantile spasms from 1 month to 2 years of age. Vigabatrin is also indicated as the adjunctive therapy for adults and pediatric patients 10 years of age and older with refractory complex partial seizures. Ideally, the vigabatrin treatment entails achieving complete seizure freedom without significant adverse effects, and the therapeutic drug monitoring (TDM) will make a significant contribution to this aim, which provides a pragmatic approach to such epilepsy care in that the dose tailoring can be undertaken for uncontrollable seizures and in cases of clinical toxicity guided by the drug concentrations. Thus, reliable assays are mandatory for TDM to be valuable, and blood, plasma, or serum are the matrixes of choice. In this study, a simple, rapid, and sensitive LC-ESI-MS/MS method for the measurement of plasma vigabatrin was developed and validated. The sample clean-up was performed by an easy-to-use method, i.e., protein precipitation using acetonitrile (ACN). Chromatographic separation of vigabatrin and vigabatrin-¹³C,d₂ (internal standard) was achieved on the Waters symmetry C18 column (4.6 mm × 50 mm, 3.5 μm) with isocratic elution at a flow rate of 0.35 mL min^-1. The target analyte was completely separated by elution with a highly aqueous mobile phase for 5 min, without any endogenous interference. The method showed good linearity over the 0.010-50.0 μg mL^-1 concentration range with a correlation coefficient r² = 0.9982. The intra-batch and inter-batch precision and accuracy, recovery, and stability of the method were all within the acceptable parameters. Moreover, the method was successfully used in pediatric patients treated with vigabatrin and also provided valuable information for clinicians by monitoring plasma vigabatrin levels in our hospital.

Levetiracetam Therapeutic Drug Monitoring in a Large Cohort of Korean Epileptic Patients

Levetiracetam is a new antiepileptic drug (AED) used for treating and preventing partial or generalized seizures. The usefulness of levetiracetam therapeutic drug monitoring (TDM) is related to inter- or intra-individual pharmacokinetic variability, drug interactions, and patient noncompliance. We aimed to investigate the levetiracetam TDM status in Korean epilepsy patients. Serum trough levetiracetam concentrations were measured using liquid chromatography–tandem mass spectrometry in 710 samples from 550 patients. The median (range) daily and weight-adjusted levetiracetam doses were 1500 (20–5000) mg and 25.5 (3.03–133.0) mg/kg, respectively. Patients on levetiracetam monotherapy constituted only 19.5% of the population, while 30.1% were on co-medication with valproate and 56.0% with enzyme-inducing AEDs (EIAEDs). Observed levetiracetam concentrations were widely distributed, ranging 0.8–95 mg/L, with a median of 17.3 mg/L. Levetiracetam concentrations were therapeutic, supra-therapeutic, and sub-therapeutic in 58.5% (n = 393), 11.6% (n = 78), and 29.9% (n = 201) of samples, respectively. There was a strong correlation between weight-adjusted levetiracetam dosage and concentrations (ρ = 0.6896, p < 0.0001). In this large-scale clinical study, a large inter-individual difference in levetiracetam pharmacokinetics was observed, and levetiracetam concentrations were influenced by EIAEDs. For individual dose adjustments and monitoring compliance, routine levetiracetam TDM is needed in epilepsy patients.

Extended-release drug formulations for the treatment of epilepsy

INTRODUCTION

Extended-release (ER) preparations are either available or have been tested for several antiepileptic drugs (AEDs). Indeed, they may be helpful in improving efficacy, tolerability, adherence, compared to the corresponding immediate release (IR) preparations available. The use of ER preparations has been advocated in women of childbearing age and is - depending on the drug - especially helpful in patients who are treated in combination with enzyme inducing AEDs as well as in children.

AREAS COVERED

Clinical and pharmacokinetic studies on ER formulations of AEDs were identified by a PubMed literature research. Further references were added from the authors' personal knowledge and from the reference lists of the identified studies. Reviews and expert commentaries were included, where necessary.

EXPERT OPINION

Unfortunately, studies providing direct comparisons of ER and IR formulations of a given drug are only available for a handful of drugs. ER preparations are especially helpful in drugs with a short elimination half-life and concentration-depending efficacy and tolerability.

Assessment of the correlations of lacosamide concentrations in saliva and serum in patients with epilepsy

Therapeutic drug monitoring of antiepileptic drugs is based on patient serum samples. In this study, we evaluated the correlation between lacosamide (LCM) steady state concentrations in serum and saliva samples. Additionally, we investigated the relation with daily dose, and assessed the feasibility of saliva collection. This was an open-label, single center study including data from 25 patients at the Bethel Epilepsy Center treated with LCM (50-650 mg/d). Samples were collected in the morning (fasting values) and in selected cases at 50 minutes to 5 hours after the morning dose. Nonsignificant differences in the mean LCM morning (trough) concentration in serum and saliva were observed. Serum and saliva concentrations across all samples were highly correlated, (r = .874), with a slightly lower correlation when only fasting values were analyzed (r = .860). Higher correlation with daily dosages was observed in serum samples (r = .773) than in saliva samples (r = .604). Serum and saliva concentrations increased significantly after intake of the LCM morning dose (P < .001). The median absolute and percentage increase of LCM in serum were moderately lower than in saliva samples, with a few outliers in saliva samples. Consequently, saliva could offer great clinical potential to monitor drug concentrations and guide LCM treatment in epileptic patients.

Brivaracetam as adjunctive therapy for the treatment of partial-onset seizures in patients with epilepsy: the current evidence base

Brivaracetam (BRV) is a novel antiepileptic drug recently licensed for the treatment of partial epilepsy in adults and adolescents over 16 years old. Like levetiracetam (LEV), it is a ligand of the synaptic vesicle protein SV2A. BRV has been shown in animal models and in studies using human brain slices to have a higher SV2A affinity and faster penetration into the brain. Its efficacy and safety have been shown in several randomized, controlled studies. The recommended initial dose is 50-100 mg, divided into two daily doses. Up-titration to a 200 mg daily dose is possible. Dizziness and somnolence are frequent side effects. There are some hints that BRV may be less frequently associated with behavioural adverse events than LEV. Long-term efficacy and safety and BRV use in special patient groups have to be assessed in the future.

Symptoms and course of intoxication with mesuximide--a case report

We report on a 31-year-old, female patient who presented with somnolence due to an intoxication by the antiepileptic drug, mesuximide (MSM). The serum concentration of its metabolite n-desmethyl-mesuximide (85.7 mg/L) was above the so-called therapeutic range (10-40 mg/L) but below the concentration range that led to an impairment of consciousness in previous cases according to the German SPC (>150 mg/L). The symptoms remitted quickly under hemodialysis. In somnolent patients treated with MSM, the treating physicians should be aware of drug intoxication as a possible etiology. Therefore, the serum concentration should be measured early. Due to the, often, long latency until the results are available, treatment initiation may be necessary based on suspicion.

Fluctuation of lacosamide serum concentrations during the day and occurrence of adverse drug reactions--first clinical experience

PURPOSE

To obtain better understanding of the effect of lacosamide (LCM) in clinical practice, laboratory and clinical data of 17 patients under treatment with LCM as an add-on antiepileptic drug (AED) were retrospectively evaluated.

METHODS

Total LCM serum concentrations were obtained at hourly intervals for up to 5h and 8h after morning dose. Adverse drug reactions (ADR) were assessed.

RESULTS

LCM serum concentrations showed high fluctuations during the day with a steep increase within the first 3h after intake (mean 87.8%; range: 44.4-149.0%) under b.i.d. Mean trough and peak concentrations of LCM were 5.0 μg/ml (range: 1.8-9.5 μg/ml) and 9.7 μg/ml (range: 4.0-18.3 μg/ml), respectively; mean dose 353 mg/d (range: 200-600mg/d). Twelve patients showed ADRs. After conversion to t.i.d. or dose reduction LCM serum concentration showed lower fluctuations during the day and a lower increase after intake (mean: 50.0%, range: 27.1-66.7%); peak LCM was 9.4 μg/ml (range: 4.7-11.6 μg/ml), mean dose 388 mg/d (range: 300-500 mg/d). These interventions led to amelioration of the ADR.

CONCLUSION

Changing the dose regimen from two to three times daily could reduce fluctuations of LCM during the day and improve tolerability of LCM in patients with ADR.